HVAC School - For Techs, By Techs

In this essential episode, Bryan Orr sits down with Elliot, the residential install supervisor at Kalos Services, to unpack a critical issue that's causing confusion among HVAC technicians, electricians, and inspectors alike: the new standards for breaker and conductor sizing on inverter-driven equipment. The conversation was sparked by Elliot's frustrating experience of having two inspectors in the same county fail the same installation for opposite reasons—one for an oversized breaker and another for an undersized breaker. This contradiction led to a deep dive into recent changes in UL standards and how they affect everyday HVAC installations. The heart of the issue stems from the transition to low-GWP refrigerants and the updated UL 60335-2-40 Edition 3 standard, which replaced the 1995 certification approach. This new standard introduced more conservative calculations for electrical characteristics, particularly affecting equipment using A2L refrigerants. The result? Data tags now show higher Minimum Circuit Ampacity (MCA) ratings than before, even though the equipment itself hasn't changed—only the math used to calculate these values has shifted. This has created a puzzling situation where the MCA can be higher than the recommended breaker size, which seems counterintuitive to anyone familiar with traditional electrical principles. Bryan and Elliot clarify the fundamental rule that still applies: size your wire to the MCA and your breaker to the MOCP (Maximum Overcurrent Protector). The confusion arises because manufacturers like Mitsubishi are now including "recommended breaker" sizes on data tags that are lower than the MCA—a courtesy to contractors, not a code requirement. The higher MCA reflects conservative safety margins that account for extreme operating conditions, but in practice, inverter-driven systems have multiple built-in protections that prevent them from ever actually reaching these calculated amperage levels. The key takeaway is that contractors can safely install breakers at the recommended size without safety concerns, as long as the breaker's lugs are rated to accept the wire size required by the MCA. The episode also explores how inverter-driven equipment fundamentally differs from traditional PSC motors, particularly regarding locked rotor amps (now more accurately termed "inverter input") and voltage drop considerations. Unlike conventional motors that simply run slower with reduced voltage, inverter-driven compressors and ECM motors compensate by drawing more current to maintain performance, creating a potential compounding effect with voltage drop that installers need to understand—even though voltage drop itself isn't an enforceable NEC code requirement. Topics Covered: New UL 60335-2-40 Edition 3 standards and their impact on electrical calculations for HVAC equipment The relationship between MCA (Minimum Circuit Ampacity) and MOCP (Maximum Overcurrent Protector) and why they can now seem contradictory Recommended breaker sizes on modern data tags and why they may be lower than the MCA Handling inspector conflicts and failed inspections related to breaker sizing Differences between inverter-driven equipment and traditional PSC motors in electrical behavior The transition from "locked rotor amps" to "inverter input" terminology for modern equipment Voltage drop considerations with inverter-driven systems (NEC 210.19A and 215.2A) Why inverter-driven equipment draws more current at lower voltages compared to traditional motors Proper wire and breaker sizing for A2L refrigerant equipment (454B systems) NEC Section 440 requirements specific to air conditioning and refrigeration equipment Breaker lug ratings and ensuring they can accept the required wire size Practical advice for communicating with inspectors and resolving code disputes   Read the tech tip on this topic HERE. Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan goes on another history journey, retelling the story of the rise and fall and rise of absorption cooling. Some of the first HVAC/R engineers cooled buildings with fire; they used absorption refrigeration, which ran on heat instead of electricity. In the early 1800s, French scientist Michael Faraday showed that gases like ammonia could absorb heat as they evaporated. Instead of compressing the vapor, engineers looked for a way to absorb the heat from the vapor and drive it back out. In 1859, Ferdinand Carré invented a machine that boiled ammonia, absorbed the vapor into water, and reheated the mixture to desorb the ammonia, creating a self-contained refrigeration machine powered by heat alone (including waste steam from boilers). This ammonia-water absorption machine could freeze water and chill brine, and it became popular in the 1880s. An absorption system has an evaporator that boils refrigerant, which is then absorbed into another liquid and creates a strong solution. Heat drives refrigerant back out of the solution as a vapor, where it is then condensed back to a liquid and metered. However, while they were reliable, they were heavy, expensive, and slow to respond. In the 1920s and 1930s, the rise of practical sealed electric compression systems began replacing absorption refrigeration infrastructure. By the mid-1900s, absorption chillers were replaced in all but a few applications. Absorption didn't completely vanish, in part thanks to Servel, which continued manufacturing absorption refrigeration systems for industrial applications and rural areas with unreliable electricity. By the 1960s, Japan and Europe refined the design with lithium bromide instead of ammonia. Absorption chillers are still present, but their complexity, maintenance demands, and poor efficiency still make them impractical for most refrigeration purposes. However, with concerns about the electrical grid and decarbonization initiatives on the rise, absorption refrigeration in hybrid systems with improved efficiency and a heat source obtained from gas turbines and biomass boilers looks promising.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this comprehensive training session from the symposium, Tony Gonzalez, Training Director at Fieldpiece, delivers an engaging and practical guide to combustion analysis for HVAC technicians. With 25 years of experience at Fieldpiece—from warehouse worker to training director—Tony brings both technical expertise and real-world application to this 50-minute interactive session focused on the company's CAT 85 combustion analyzer. Tony emphasizes that combustion analysis serves four critical purposes: safety, efficiency, equipment specification verification, and liability protection. He makes a compelling business case for investing in combustion analyzers, noting that preventing just two callbacks or one liability lawsuit can pay for the equipment ten times over. The training walks attendees through the complete process, from properly warming up the analyzer in fresh air (allowing sensors to calibrate to ambient oxygen and zero carbon monoxide) to generating professional PDF reports that can be shared with customers or integrated into work order management systems like ServiceTitan. The session provides detailed guidance on interpreting key measurements, including stack temperature, oxygen percentage, carbon monoxide levels, and draft pressure. Using design parameters from the National Comfort Institute, Tony demonstrates how to diagnose issues by comparing actual readings against acceptable ranges for different furnace types (atmospheric, 80% induced fan, and 90+ percent condensing). He walks through practical troubleshooting scenarios, showing how measurements like high oxygen combined with low stack temperature can point to specific problems like low gas pressure that technicians can then verify and correct. Throughout the presentation, Tony emphasizes proper technique and best practices, from creating test ports at least 12 inches above the inducer fan to the importance of plugging test ports after completion. He also highlights innovative features of Fieldpiece's analyzers, including the hydro cycle pump that eliminates traditional water traps, sensor vault technology that extends sensor life to four years, and built-in wireless connectivity allowing technicians to view measurements on their mobile devices through the Job Link app. Topics Covered: Why perform combustion analysis: Safety verification, efficiency optimization, OEM specification compliance, and liability protection Business benefits: Reducing callbacks, improving OEM relationships, enhancing professional image, and protecting against lawsuits Proper startup procedure: Warming up analyzers in fresh air for accurate oxygen and CO sensor calibration Ambient CO testing: Using combustion analyzers vs. dedicated walk-around detectors for carbon monoxide detection in living spaces Test port installation: Proper placement at least 12 inches above inducer fans and away from 90-degree elbows Key measurements explained: Stack temperature, oxygen percentage, CO PPM, CO air-free, draft pressure, and efficiency calculations Equipment type selection: Choosing correct settings for atmospheric, 80% induced fan, or 90+ percent condensing furnaces Diagnostic interpretation: Using National Comfort Institute parameters to identify issues like excess combustion air or low gas pressure Advanced features: Built-in dual port manometer for gas and static pressure, wireless Job Link app connectivity, and hydro cycle pump technology Report generation: Creating professional PDF reports with company branding for customer documentation and CYA protection Maintenance tips: Checking particle filters, understanding sensor vault technology, and the importance of annual calibration Sensor longevity: Four-year sensor life warranty and field-replaceable sensors without sending equipment for service   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, we go back into the history of the trades, namely the battle over frequency (and how each side had to give until it hertz). The low hum of motors is alternating current: electricity moving back and forth through copper 60x per second (in the USA and Canada, at least). In another version of history, that pulse could be 50x per second instead (as in much of the remainder of the world). The forgotten frequency war is the lesser-known sequel to the war of the currents. Tesla's AC power prevailed over Edison's DC, but different motor and generator companies chose different alternating current frequencies. Westinghouse chose 60 cycles per second, whereas General Electric experimented with 25-40 cycles per second, and Europe-based Siemens and AEG standardized around 50 hertz. These different frequencies set the rhythm for everything that turns or glows, and electric parts that didn't match often failed. Nevertheless, the engineers of the companies defended their own frequencies. In the 1910s, the US began merging electrical grids to set a single standard. Westinghouse had the most dominant technology at the time, and 60 hertz became the norm in the USA. However, across the pond, 50 hertz made more sense for the European infrastructure that was in place and being rebuilt after WWI, and it was solidified by the rebuilding efforts of WWII. As a result, roughly 2/3 of the planet uses a 50-hertz frequency. The two frequencies are incompatible because motors will travel at a different speed than their design while drawing the same current, leading to reduced capacity or overheating. In the 1960s, international companies produced dual-rated compressors and motors, but global trade is still complicated by different frequencies, and moving entirely to a single frequency is impractical due to the infrastructure disruption required. However, modern VFDs and inverter technology can change frequencies as they enter the motor, thus solving the battle over frequency and reminding us that flexibility is the real future.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this candid conversation, Nathan and Bryan dive deep into the often-misunderstood world of sales in the construction and HVAC trades. Nathan, who has transitioned from fieldwork to spending roughly 60% of his time in sales, offers a unique perspective on why sales professionals are necessary despite the skepticism they face from tradespeople. The discussion tackles head-on the negative perceptions surrounding salespeople while making a compelling case for their essential role in growing and sustaining a trades business. The conversation explores the fundamental differences between residential and commercial sales, revealing insights that anyone in the industry will find valuable. Nathan explains that residential sales requires quick relationship-building, subject matter expertise, and the ability to emotionally connect and disconnect rapidly from customers you may only see every few years. It's essentially retail sales with a technical component. Commercial B2B sales, on the other hand, is far less transactional and much more relational—it's about building confidence, managing accounts effectively, and ensuring clients can focus on their core business while you handle their facility problems seamlessly. One of the most refreshing aspects of this discussion is Nathan's honesty about the unglamorous side of sales. He emphasizes that the job isn't about fancy lunches or golf outings—it's about being the person who answers their phone, follows through on commitments, and doesn't shy away from uncomfortable conversations. The guys share frustrating examples of poor salesmanship, from ghosting potential clients to making promises that can't be kept, illustrating how these failures give the entire profession a bad reputation. Nathan stresses that good sales is fundamentally about managing expectations, delivering on promises, and serving as the crucial liaison between customer needs and production capabilities. The conversation concludes with practical advice for tradespeople considering a move into sales: if you're motivated by the chase, enjoy solving people's problems, and find satisfaction in knowing your work directly impacts the bottom line, sales might be for you. But if you're just looking for an easier path with less physical labor, think again—great salesmanship is mentally demanding work that requires constant follow-through and resilience. Topics Covered: Why tradespeople are often critical of sales and the misconceptions about the profession The difference between "good" and "bad" salespeople and the moral use of sales skills Essential traits for successful residential HVAC salespeople, including product knowledge and emotional agility How commercial B2B sales differs from residential—less transactional, more relational The critical importance of follow-through, responsiveness, and keeping promises in account management Why sales serves as the essential "oil in the machine" that prevents business breakdowns The role of salespeople in managing customer expectations and protecting production teams The unsexy reality of sales work: constant uncomfortable conversations and problem-chasing When entertaining clients (golf, lunches) is appropriate versus when it becomes buying work Advice for tradespeople considering transitioning into sales roles   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan takes us on a history journey back to when ammonia ruled the world. In the mid-1800s, before R-12, many inventors and scientists experimented with vapor-compression refrigeration systems to make ice. They used a variety of refrigerants in their patents, including ether, ethyl ether, carbon dioxide, sulfur dioxide, methyl chloride, and ammonia. Each one had tradeoffs, but ammonia was the favorite because it was inexpensive, very good at moving heat, and useful because its odor made leaks obvious (although it was toxic and irritated the lungs and mucus membranes). Toxic refrigerants, particularly sulfur dioxide and methyl chloride, were common refrigerants but had plenty of negative press due to the many deaths they caused. In response to the public's reservations about toxic refrigerants, Thomas Midgley from General Motors (who developed leaded gasoline) teamed up with Charles Kettering and DuPont to find a refrigerant that was non-toxic, non-flammable, and non-corrosive. In 1930, they announced dichlorodifluoromethane, also known as R-12 (a CFC) and trademarked as Freon. This refrigerant was non-toxic, non-flammable, and had no odor, and it effectively replaced the methyl chloride, sulfur dioxide, and ammonia. However, many decades later, scientists discovered that chlorine-bearing compounds were destroying the ozone layer. To combat the environmental damage, many nations signed the Montreal Protocol in the 1980s, which would effectively phase out R-12, R-11, and other CFC refrigerants. Over time, the regulations have tightened on HCFCs and high-GWP HFCs, leading us to where we are now with lower-GWP A2L HFCs and HFO blends. As with the old refrigerants, each refrigerant had a tradeoff. Meanwhile, this whole time, ammonia never became truly obsolete and quietly remained the lifeblood of industrial refrigeration, and it also had no global warming potential OR ozone-depletion potential. Ammonia systems run with relatively little charge, especially when paired with CO2, and ammonia is still a powerhouse today because of its chemical formula (NH3), good compression ratio, and excellent latent heat of vaporization. Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this episode of the HVAC School podcast, Bryan and Nathan dive deep into the challenges of humidity control in grocery stores and other refrigerated environments. While the conversation takes several entertaining detours (including discussions about morning radio shows, Indian weddings with elephants, and imaginary lava-heated homes), the core content provides valuable insights for HVAC and refrigeration technicians dealing with condensation and moisture issues in commercial refrigeration spaces. The hosts explain why humidity management is critical in grocery environments, where refrigerated cases and displays must maintain cold temperatures while preventing condensation on doors, frames, and floors. They discuss the evolution from traditional solutions—like energy-intensive frame heaters that kept surfaces above dew point—to modern strategies involving dedicated outdoor air systems (DOAS), strategic use of waste heat from refrigeration racks, and various dehumidification approaches. Nathan emphasizes that the key is maintaining proper dew point levels (typically targeting 45% relative humidity at around 72°F) while keeping the building under positive pressure to control moisture infiltration. A significant portion of the discussion focuses on airflow management and its impact on refrigeration equipment. The hosts explain how air curtains in display cases work on Bernoulli's principle to maintain cold temperatures, and why even minor disruptions to airflow patterns can cause product spoilage or increased energy consumption. They stress the importance of understanding building pressure dynamics, especially considering makeup air requirements for exhaust systems in sculleries and loading docks. The episode concludes with practical troubleshooting advice for technicians dealing with sweating cases and humidity problems. Nathan recommends systematically checking building pressure with a manometer, measuring dew point at multiple locations throughout the store, and verifying that door and frame heaters are functioning properly. He also suggests looking for intermittent fresh air sources and exhaust fans that might be disrupting the carefully balanced airflow patterns that keep moisture under control. Topics Covered: Dew Point vs. Relative Humidity: Why focusing on dew point (50-55°F typical target) is more important than relative humidity in grocery environments Condensation Prevention Strategies: Evolution from energy-intensive frame heaters to modern DOAS systems with reheat capabilities Airflow and Air Curtains: How Bernoulli's principle creates invisible barriers in refrigerated display cases and why disrupting these patterns causes problems Reheat Methods: Various approaches, including waste heat from refrigeration racks, electric reheat, and desiccant dehumidification systems Building Pressure Management: Importance of maintaining positive pressure while managing fresh air requirements and exhaust systems Radiant Heat Effects: How surface temperatures, not just air temperature, affect condensation on refrigerated cases Troubleshooting Humidity Issues: Systematic approach to diagnosing moisture problems, including pressure testing, dew point measurement, and identifying intermittent airflow sources Return Air Placement: Benefits of pulling return air from underneath cases to capture the most humid air for dehumidification   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan explores the history of the finned-tube coil, which is what we use for heat exchange in air-source air conditioners and heat pumps. Air-source HVAC systems have copper tubes threaded through thin metal fins. This design was optimized to ensure the greatest possible surface area for heat exchange to occur. However, prior to the finned-tube coil, HVAC coils looked more like plumbing projects with bare copper loops, which were heavy, costly, and inefficient.  In the early 1900s, HVAC was essentially plumbing with higher expectations; capacity was dictated purely by size and charge. In the 1910s and 1920s, early air conditioning pioneers were already attempting to increase surface area with metal discs or pipes, which evolved to continuous sheet fins. The tube would move refrigerant, and the fins would collect heat from the air and pass it into the tube; the finned-tube coil was born. The added weight was minimal, but the contact area was increased by almost 3000%, meaning coils and charges could be smaller with added efficiency. This move was necessary because while we already knew that heat can indeed move without touching molecules (radiant transfer), radiant cooling had a unique challenge: dew point. Finned-tube coils rely on convection and only have temperatures below the dew point in a small area, which allows us to have a small drain pan. Aluminum was also plentiful after WWII, enabling finned-tube technology to evolve to louvered fins and reach the masses. By the 1960s, finned-tube coils were in all sorts of applications. However, it became clear that aluminum was fragile, and we have since innovated to overcome that challenge. There are three barriers that heat transfer must overcome: air-side film resistance (air is a poor conductor), wall conduction through the tube and fins, and refrigerant-side film resistance (oil inside or laminar flow). The fins help with air-side film resistance, so we want to clean and straighten them as much as possible.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this comprehensive episode of the HVAC School podcast, host Bryan Orr sits down with three experts from Copeland to demystify tandem and trio compressor systems. Joining him are Gina Kahle (Multiples Engineering Manager with 12+ years at Copeland), Tyler Daniels (Product Management team member), and James Stevenson (Technical Sales veteran with 28 years of field experience). Together, they provide both the engineering perspective and real-world service insights that technicians need to understand these increasingly common systems. The conversation begins with the fundamentals: tandem and trio systems represent an evolution in compression modulation, allowing multiple compressors to work together on a single circuit rather than requiring separate circuits for each compressor. This design philosophy delivers significant advantages, including energy savings through better modulation, simplified system design, reduced costs, and the ability to meet stringent minimum modulation requirements (such as the 25% threshold for units under 60,000 BTUs per hour). The team emphasizes that tandems aren't just about pairing any two compressors together—Copeland engineers carefully consider application requirements, flow characteristics, and stress testing to ensure reliable oil management and system resonance control. A major focus of the discussion centers on practical service considerations that every technician needs to understand. James provides invaluable guidance on identifying whether a failed compressor in a tandem system can be replaced individually or requires replacing the entire tandem assembly. The "rule of thumb" is clear: compressors small enough to fit in residential systems (typically under 10 horsepower or about 7 inches in diameter) generally require full tandem replacement, while larger units may allow single compressor replacement. The distinction between "tandem ready" and non-tandem ready compressors becomes critical here—larger compressors (10+ horsepower) are typically sold tandem ready at wholesalers with the necessary oil equalization ports and sight glass connections, while smaller units are not. The episode also explores advanced topics, including the integration of Enhanced Vapor Injection (EVI) technology with tandem systems, particularly for cold climate heat pump applications. Gina explains how EVI extends the operating envelope down to -40°F, opening new markets and applications. The team discusses the transition to A2L refrigerants and how Copeland continues to innovate despite changing regulatory landscapes. Throughout the conversation, they emphasize the critical importance of proper oil management through oil equalization lines (OEL) and two-phase transfer lines (TPTL), and why maintaining these connections exactly as designed is non-negotiable for system longevity. Key Topics Covered: Tandem and Trio Basics: Definition and benefits, including energy savings, cost reduction, and design simplification Modulation Requirements: Meeting state-mandated minimum modulation thresholds (25% for units under 60,000 BTU/hr) Applications: Data centers, DOAS units, rooftops, chillers, and various commercial spaces Compressor Pairing Options: Fixed speed, digital, variable speed, two-stage, and mixed configurations Oil Management: Critical importance of oil equalization lines (OEL), two-phase transfer lines (TPTL), and gas equalization lines (GEL) Service and Replacement: How to identify tandem-ready vs. non-tandem-ready compressors; when to replace individual compressors vs. full tandem assemblies Visual Identification: Using compressor size (7" vs 9" diameter), port configuration, and horsepower ratings to determine replacement strategy Piping Configurations: Three-pipe vs. four-pipe designs and when each is necessary Installation Considerations: Importance of keeping oil equalization lines level (parallel to ground) and using proper mounting spacers Enhanced Vapor Injection (EVI): How EVI technology extends operating envelopes to -40°F for cold climate heat pump applications Energy Efficiency Standards: Meeting IEER, IPLV, and upcoming IVEC standards through strategic tandem use Copeland Mobile App: Features, including parts lookup, resistance specifications, amperage mapping, AI Scout assistant, and technical bulletins   Learn about the Copeland Mobile app at https://www.copeland.com/en-us/tools-resources/mobile-apps/copeland-mobile.  Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan tells the story of the technology that tried to beat the compressor... and still may someday. We associate cooling with refrigerant... and all the things that come with it, including compressor noise, oil, recovery machines and tanks, leaks, superheat, and regulations. However, there is a means of providing cooling with two pieces of metal and several semiconductors; current runs through it, and one side becomes cold, and the other side becomes hot. This technology is called thermoelectric cooling, associated with the Peltier effect. In 1834, French watchmaker and amateur physicist Jean Charles Athanase Peltier was experimenting with electricity and dissimilar metals. When he joined two wires of different materials and ran current through the junction, one got colder, and the other one got hotter. This phenomenon was named the Peltier effect, and it describes how passing electrical current through two dissimilar conductors causes heat to move from one side to the other, like a tiny reversible heat pump. However, it didn't have any practical use at the time. Semiconductors arrived in the mid-1900s, and engineers could make thermoelectric devices strong enough to move meaningful amounts of heat. In the 1960s, NASA even began using the technology in spacecraft for precision temperature control, which was hardy and allowed them to stabilize sensors and electronics in space. We began using them on Earth in some specialized applications, including portable coolers, wine chillers, and CPU coolers in computers. However, this technology didn't replace vapor-compression refrigeration due to efficiency constraints and the need to reject heat. Thermoelectric modules are only 5-10% as efficient as vapor-compression systems, and they need heat sinks or fans to give the heat somewhere to go. We've still been pursuing a comfort cooling use of the Peltier effect, and we've gotten closer, but most applications still have the efficiency block. When efficiency isn't a problem, we encounter difficulties with moisture and latent heat removal. Nevertheless, thermoelectric cooling is still making a difference for sensors and in localized cooling applications.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this comprehensive episode, Bryan and Roman dive deep into one of the most challenging topics in modern HVAC: making VRF (Variable Refrigerant Flow) and ductless systems perform effectively in humid climates like Florida. The conversation tackles a common misconception that inverter-driven equipment automatically handles humidity well simply because it can "turn down." Roman emphasizes that successful application of VRF technology in humid environments requires skilled professionals who understand building science, envelope integrity, and proper system sizing. The biggest takeaway? If you're going to err on sizing, undersize rather than oversize - these systems will run longer and maintain better humidity control when properly sized. The hosts explore the three critical factors for dehumidification: runtime, coil temperature, and surface condensation. They explain how traditional inverter systems were programmed for energy efficiency by allowing coils to warm up as they approached the set point, which unfortunately sacrifices latent capacity. Modern systems with active dehumidification capabilities use expansion valve control to "starve" the coil, lowering saturation temperature to around 35-37 degrees while extending runtime. Roman shares his personal experience with a 7,000 BTU unit serving his 700 square foot master bedroom suite, demonstrating how proper application and understanding of equipment capabilities can deliver excellent humidity control without oversizing. The discussion takes a practical turn as Bryan presents a comprehensive troubleshooting checklist for humidity problems, starting with bulk water leaks and progressing through envelope integrity, duct sealing, equipment selection, and pressure balancing. They debunk common "solutions" that actually make problems worse, like adding attic insulation or solar attic fans without addressing root causes. The conversation reveals a counterintuitive truth: reducing sensible load through excessive insulation can worsen humidity problems by reducing equipment runtime. They explain why "active dehumidification" through overcooling isn't true dehumidification, and why another solution - reheat - requires adding sensible heat back to spaces to maintain longer equipment runtime. Topics Covered: VRF and inverter sizing misconceptions - Why undersizing is often better than oversizing in humid climates Three factors of dehumidification - Runtime, coil temperature, and surface condensation explained Active dehumidification technology - How expansion valve control creates longer runtime and colder coils Equipment capacity ratings - Understanding that a "12K" unit may actually perform at 18,000 BTU Latent vs. sensible capacity - Why checking engineering specifications is critical for humid climate applications VRT (Variable Refrigerant Temperature) - When this energy-saving feature should be disabled in humid climates Fan operation strategies - Why continuous fan operation can worsen humidity problems Duct and envelope leakage - How pressure imbalances drive moisture problems Surface condensation - Why vents and ducts sweat and how to prevent it The overcooling trap - Why lowering the set point creates interstitial space moisture problems Humidity sensors in thermostats - Understanding what they do (and don't do) Load diversity and zone control - How multiple smaller units can outperform single large systems Reheat strategies - From electric resistance to passive solar gain Common mistakes - Why attic insulation and solar fans often worsen humidity issues Troubleshooting checklist - A systematic approach from bulk water to equipment selection   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast, Bryan gives another history lesson and goes over the history of the thermostat. Before 1883, automatic temperature control simply did not exist; we shoveled fuel into the furnace and opened windows. If a room got too hot in a commercial building, the janitor would go downstairs to choke the draft damper; this person was responsible for manually controlling comfort. Warren S. Johnson, a Milwaukee-based college professor, sought to do something about his classroom's sweltering heat. He created a pneumatic thermostat that mounted to the wall, sensed temperature, and used air pressure and mechanical systems to control dampers. This invention grew in popularity, and he founded Johnson Controls. Compressed air ran entire HVAC networks by adjusting dampers and valves before electricity went mainstream. Engineers experimented with bi-metallic strips, which could open or close an electrical circuit based on temperature changes, which made thermostats smaller and cheaper. Honeywell came on the scene by hiring industrial designer Henry Dreyfuss, who invented the mercury thermostat: the T87 round thermostat. When the bimetal coil tilted, mercury rolled from one end to the other to complete or open the circuit. These thermostats had a heat anticipator, which kept them from overshooting the temperature. Unfortunately, when these thermostats were disposed of, the mercury polluted the environment and affected the central nervous system. The digital thermostat came on the scene to replace the mercury thermostat, which led to the development of the Nest smart thermostat. However, all this time, comfort has been associated with the number on the thermostat; smart comfort controls that learn our routines and monitor dew point, relative humidity, and IAQ are the next step to create true comfort and health.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this candid and comprehensive episode, Bryan sits down with Roman to tackle one of the most frustrating yet crucial aspects of the HVAC industry: technical support. What starts as a conversation about their own tech support nightmares quickly evolves into a deep dive examining the entire ecosystem—from manufacturers and distributors to technicians and sales reps—and how each player can improve the support experience. Roman opens up about his recent tech support struggles, including having to search Russian websites just to find service manuals for major brand equipment. This leads to a broader discussion about the fundamental problem: as HVAC equipment becomes increasingly complex with proprietary controls and advanced technology, manufacturers have simultaneously made it harder to access the information needed to service that equipment. The conversation highlights how the old "I never called tech support" mentality of veteran technicians is no longer viable when you're dealing with VRF systems, building automation, and equipment-specific protocols that require specialized knowledge. The hosts emphasize that good documentation isn't just helpful—it's essential, and manufacturers who hide behind "brand protection" are actually damaging their reputation in the long run. The episode doesn't just complain about problems; it offers real solutions. Bryan and Roman discuss what technicians need to do before calling tech support (hint: know your superheat, subcooling, and basic electrical readings), what makes great tech support personnel, and why investing in these roles pays dividends. They share inspiring examples of distributors and reps who go above and beyond, like the Johnstone team in Louisiana who actively seek out field experts when manufacturers can't provide answers. The conversation also touches on why tech support and education roles are chronically underpaid, and how properly compensating and supporting these positions could transform the industry. Perhaps most importantly, the hosts emphasize that everyone in the HVAC ecosystem is working toward the same goal: keeping end clients comfortable and satisfied. When manufacturers, distributors, reps, contractors, and technicians recognize this shared objective and work collaboratively rather than defensively, everyone wins. The episode concludes with practical advice for sales professionals, including the importance of ride-alongs and adopting the "I got it" mentality that turns good salespeople into indispensable partners. Topics Covered Service Manual Accessibility: The critical need for manufacturers to make documentation easily searchable and available online, not hidden behind outdated processes Manufacturer Responsibilities: Why "protecting the brand" often backfires and how transparency builds loyalty Technician Preparation: What basic measurements and troubleshooting steps should be completed before calling tech support Tech Support Personnel: The importance of properly compensating and supporting tech support staff to reduce burnout and turnover Distributor and Rep Excellence: How the best wholesalers and reps go beyond just forwarding emails to actively solve problems The "I Got It" Sales Approach: Why taking ownership of customer problems is the key to building lasting relationships Cross-Brand Part Referencing: The need for universal parts cross-referencing across sister brands and product lines Field Ride-Alongs: Why B2B sales professionals should spend at least one day per month in the field with technicians Legacy Product Support: The frustration when manufacturer partnerships dissolve and orphaned equipment becomes unsupportable AI in Tech Support: Why throwing technology at support problems without understanding the root issues is a waste of money   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan is back for yet another history lesson. This time, the subject is the current war with Tesla, Edison, and Westinghouse. The current war was fought in the late 1800s with lightbulbs, electrocutions, and a World's Fair that dazzled the entire world. Edison didn't necessarily invent the lightbulb, but he made it commercially viable by inventing the infrastructure needed to make it work; electricity worked one way and performed well in small cases. However, voltage drop was a problem with direct current (DC) circuits; Edison was okay with decentralized (localized) power generation with centralized control under the Edison Electric Light Company.  Tesla proposed a system using alternating current (AC), which could be sent hundreds of miles with minimal loss thanks to a transformer (which could step down high voltages from the utility source). AC power steps up at the utility and then down at several points between the utility source and the end user. This vision was at odds with Edison's DC system. Tesla, who had worked under Edison, sold his patents to George Westinghouse. Edison began a propaganda campaign against AC power, emphasizing its dangers. However, Tesla harnessed the powers in his lab to demonstrate its potential; while impressive, it didn't necessarily prove the safety to the public. The Chicago World's Fair was the battleground of the current war: both Edison and Westinghouse submitted bids, and the latter's was half the price. The World's Fair was lit purely by AC power and proved its usefulness to the world (primarily to Westinghouse's financial benefit). DC faded into obscurity as a means of powering cities, and although Edison was a showman and salesman, his invention was upstaged when it mattered most. However, DC made a comeback over a century later, particularly with the rise of electronics, LED drivers, and solar power. It can now move power over ultra-long distances, too.    Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this raw and unfiltered episode, Bryan sits down with Elliot, a senior service tech and newly minted install supervisor, to discuss the realities of working with R-454B refrigerant in the field. What starts as a technical discussion about the new A2L refrigerant quickly evolves into a candid conversation about industry frustrations, manufacturer accountability, and the practical challenges technicians face with the latest refrigerant transition. With four years of hands-on experience, Elliot brings fresh perspectives on everything from charging procedures to equipment reliability issues. The conversation takes an honest look at the R-454B rollout, which Bryan describes as a massive industry failure. Unlike typical manufacturer talking points, this episode dives into real problems technicians are experiencing: extended charging times, subcooling drift, and equipment component failures. Bryan and Elliot discuss how R-454B systems can take up to an hour to stabilize compared to the 15-20 minutes they were accustomed to with R-410A. This isn't just an inconvenience—it's affecting how technicians approach charging procedures and follow-up visits. The episode also explores theoretical explanations for R-454B's unusual behavior. Bryan presents two hypotheses about why the refrigerant takes so long to reach equilibrium: either density differences between R-32 and R-1234yf are causing stratification in the condenser, or one component is settling at the top and acting like a non-condensable. While admitting he's "not a mathy details guy," Bryan encourages field technicians to investigate these phenomena using thermal imaging cameras and careful observation. This practical, boots-on-the-ground approach to understanding new technology exemplifies the podcast's commitment to real-world problem-solving. Beyond technical discussions, the conversation touches on broader industry issues, including the politics behind refrigerant selection, manufacturer warranty support (or lack thereof), and the challenges faced by contractors trying to maintain fair pricing while dealing with new equipment failures. Bryan and Elliot also address the reliability concerns with new A2L safety components like dissipation boards and refrigerant sensors, noting that while failure rates aren't dramatically higher than other components, they represent additional potential failure points that weren't previously necessary. Topics Covered R-454B Charging Behavior: Extended stabilization times (up to 1 hour vs. 15-20 minutes for R-410A) and subcooling drift over time Field Charging Strategy: Why technicians are intentionally undercharging slightly and relying more on line length specifications A2L Safety Components: Dissipation boards and refrigerant leak sensors—their function, failure rates, and nuisance alarms Refrigerant Stratification Theory: Potential explanations for delayed equilibrium involving density differences and non-condensable behavior Industry Politics: The R-454B vs. R-32 debate, GWP legislation, and lobbying efforts that shaped current refrigerant standards Manufacturer Accountability: Warranty support issues, untested components, and the financial burden on contractors Recovery and Reuse Concerns: Questions about blend consistency when recovering R-454B and tank contamination issues Future of HVAC: Discussion of heat recovery chillers, secondary fluid systems, and emerging refrigerant-free technologies Pressure Testing Requirements: New legislation requiring extended pressure tests and improved brazing practices Practical Field Advice: Using thermal imaging to diagnose condenser behavior and verify proper refrigerant distribution   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan talks about psychrometrics and the magic line inside a messy-looking chart. The psychrometric chart is a key tool for understanding the relationship between air and water. "Psychrometric" comes from the Greek roots for "cold" and "measurement." As such, a tool called the psychrometer (with paired wet-bulb and dry-bulb thermometers) could measure two different temperatures, and we could use these to determine how much water vapor the air can hold (even though the air doesn't "hold" water vapor; it's all about vapor pressures).  The psychrometric chart was developed with the contributions of James Apjohn and William Ferrell in the 1800s, but Willis Carrier was the one who drafted the paper titled "Rational Psychrometric Formulae" in 1911. He created a chart that plotted temperature, humidity, and enthalpy on a single piece of paper. The horizontal axis represents the dry-bulb temperatures, the curved lines represent relative humidity, the left axis represents humidity ratios, the diagonal lines represent wet-bulb temperatures, and the other angled lines represent enthalpy. Every possible air condition can be plotted on the chart. Moving horizontally changes sensible heat (temperature), and moving vertically changes latent heat (moisture content); both are critical to human comfort. The "magic line" is the dew point. When this line is crossed, that's when surfaces like ducts or HVAC coils begin to sweat, as air can't hold any more moisture. You can use this information and the psychrometric chart to help you make sense of customer complaints (e.g., "clammy") and predict how air and moisture will behave if you adjust airflow or add insulation.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this episode of the HVAC School podcast, Bryan sits down with Ray Wohlfarth, a seasoned HVAC contractor and prolific author who has dedicated over 30 years to mastering the art and science of boiler systems. What began as a competitive disadvantage—competitors claiming he knew nothing about boilers—became Ray's driving passion. Through daily reading, countless mistakes, and an unwavering commitment to learning, Ray transformed himself into one of the industry's most respected voices on hydronics and steam systems. Ray shares the personal story of how legendary author Dan Holohan literally "saved his marriage" with his book on one-pipe steam systems. When Ray and his wife moved into their first house with steam heat, mysterious banging sounds threatened domestic harmony until Dan's book provided the answers Ray desperately needed. This experience inspired Ray to pay it forward, eventually authoring 14 technical books himself—all written with the vision of a technician stuck in a boiler room at 9 PM on a Friday night, frantically searching for solutions. The conversation dives deep into practical wisdom earned through experience. Ray emphasizes the critical importance of safety in boiler rooms, recounting a harrowing story of a hospital engineer who bypassed safety controls and manually lit a boiler with a flaming broom—resulting in dangerous explosions. He stresses that technicians should always identify escape routes before beginning work, as a lifting relief valve can quickly fill a room with steam, displacing oxygen and eliminating visibility. Beyond safety, Ray shares diagnostic techniques like listening for dripping, hissing, or the "Rice Krispies" sound that indicates scaling, and visually inspecting for soot streaks that reveal combustion problems and potential carbon monoxide issues. Throughout the episode, Ray's philosophy shines through: humility, continuous learning, and the joy of solving complex problems. Whether discussing the holistic nature of steam system troubleshooting, the importance of water quality treatment, or the surprising efficiency of properly designed steam systems (like the LEED Gold-certified Empire State Building), Ray's expertise and passion are evident. His advice for aspiring boiler techs is simple but profound: read 15 minutes daily about your industry, engage with online communities like HeatingHelp.com, and never stop learning from every service call. Topics Covered Ray's Journey: Transitioning from Carrier air conditioning to boiler expertise over 30+ years The Writing Process: Creating 14 technical books designed specifically for technicians in the field Dan Holohan's Influence: How Dan's books and mentorship shaped Ray's career and literally saved his marriage Boiler Room Safety: Critical importance of identifying escape routes and recognizing dangerous practices Diagnostic Techniques: Using your senses—listening for dripping, hissing, and scaling sounds; looking for soot, leaks, and discoloration Near-Boiler Piping: Why 90% of steam boiler installations have incorrect piping and the importance of proper insulation Steam vs. Hydronic Systems: Key differences in troubleshooting approaches and why steam operates more like air conditioning than hydronic One-Pipe vs. Two-Pipe Steam: Fundamentals of steam system design, traps, and venting behavior Condensing Boilers: The reality of "conditional condensing" and why 95% efficiency requires specific return water temperatures Radiant Heat Comfort: Why hydronic radiant heating provides superior comfort compared to forced air Water Quality Issues: The critical importance of water treatment, the mystery of deteriorating fittings, and potential chlorine impacts Learning Resources: The value of HeatingHelp.com, reading 15 minutes daily, and engaging with online communities Ray's Book Series: Overview of his "Lessons Learned" series and specialized books on brewery boilers and wiring diagrams Common Mistakes: Real-world troubleshooting stories including the mystery of the 2-degree delta T and lessons in humility   Check out some of Ray's boiler books on Amazon HERE. His latest book, Lessons Learned: Understanding Boiler Wiring Diagrams, is available HERE. Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan explains how duct tape got its name and why it shouldn't actually be used on ducts. Duct tape is a versatile home DIY-fix tool, but despite its name, it wasn't initially made to seal ducts at all. In 1943, we were in the thick of World War II, and ammo shipments were sealed with wax and paper tape. These were often not durable or difficult to open. Johnson & Johnson developed a tape with rubber adhesive on a cotton duck cloth backing (which was already widely used for military uniforms and tent fabrics). This new tape was nicknamed "duck" tape due to the material and its waterproof abilities (like the waterfowl). A woman named Vesta Stoudt informed President FDR about duct tape, and the War Production Board began using it in wartime supply packaging. After the war, America had a housing boom in the 1950s, which included the demand for forced-air heating and cooling systems. Marketers thought the tape could seal the ducts in those homes, so they changed the color to match sheet metal and rebranded it as "duct tape." In the 1960s, this tape was available in retail outlets with the "duct tape" branding. Unfortunately, in tests by the Lawrence Berkeley National Lab, duct tape failed miserably at sealing the ducts because the rubber adhesive dries out under heat, and dust weakens the adhesive. As a result, many building codes ban duct tape on ducts (spearheaded by California). Instead, UL-listed foil tape and mastic are approved for sealing ducts. However, duct tape still became famous for its versatility as a patching material. It's prevalent in pop culture and has been used in television shows and even in space.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this comprehensive discussion, Bryan and Bert tackle one of the most critical yet underdeveloped skills in the trades: conflict resolution and de-escalation. They argue that poor conflict management is one of the primary reasons technicians lose jobs, damage team dynamics, and limit their career advancement. The conversation explores both customer-facing conflicts and internal team disputes, offering practical strategies grounded in real-world experience. The hosts distinguish between rational and irrational customer anger, noting that both require similar approaches—taking clients seriously, listening fully, and resisting the urge to immediately correct or defend. Bert emphasizes the importance of body language, describing how he physically leans into difficult conversations rather than backing away, making eye contact, and allowing customers to repeat themselves until they feel genuinely heard. Bryan adds that the "slow is smooth, smooth is fast" military principle applies perfectly to people problems—rushing to fix the emotional situation often prolongs the conflict, while patient listening typically resolves issues more quickly. When addressing internal team conflicts, they stress going directly to the person involved rather than gossiping or complaining to management. Both hosts acknowledge that ego, the need to be right, and past trauma can trigger fight-or-flight responses that sabotage productive conversations. They advocate for approaching conflicts with humility and a willingness to be wrong, focusing on the single most important issue rather than bringing up a laundry list of grievances. Bert shares that preventing conflict often means letting minor issues go while addressing patterns before they fester into major problems. The conversation concludes with practical advice about maintaining relationships after difficult conversations, recognizing that drawing back creates rejection while intentionally staying connected demonstrates genuine care. They emphasize that mastering conflict resolution isn't just about keeping your job—it's about becoming invaluable in your career and developing skills that serve you in every area of life. Topics Covered: Common sources of customer anger: feeling dismissed, not taken seriously, fear around property damage, and frustration with time and money The difference between rational emotions (legitimate grievances) and expectation gaps (perceived as "irrational") Body language techniques for de-escalation: leaning in, maintaining eye contact, staying present rather than fleeing Why interrupting customers to prove you're right backfires and escalates conflict Managing fight-or-flight responses and recognizing when fear drives aggressive reactions The importance of letting customers repeat themselves until emotional release occurs Internal team conflict triggers: lack of recognition, perceived unfair workloads, misinterpreted communication Why going directly to the person involved beats gossiping or complaining to management The danger of storytelling and assigning motives to others' actions Practical conflict resolution framework: prepare both parties, choose private settings, listen twice as much as you speak, and be willing to be wrong How mastering conflict resolution makes you invaluable and accelerates career advancement Maintaining relationships after difficult conversations to avoid creating rejection   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android

In this spooky Halloween short podcast episode, Bryan tells the story of the cooling tower killer: Legionnaires' disease. In the summer of 1976, the nation celebrated its bicentennial anniversary. The American Legion was holding its 58th annual convention at the Bellevue Stratford Hotel in Philadelphia, PA. In the days following the convention, doctors in Philadelphia started noticing dozens of Legionnaires in their hospitals with high fevers, chills, coughs, and difficulty breathing. Their symptoms resembled those of pneumonia, but patients deteriorated quickly, and antibiotics didn't work as expected. People became more ill, and 34 of them died. There were many theories, from food poisoning to novel viruses to bioterrorist attacks. The CDC investigated biological samples from patients and swabs from the hotel alike, but their findings were inconclusive. As news outlets sensationalized speculation over the cause of the illnesses, the disease was named after the unfortunate Legionnaires who suffered from it. However, the speculation would come to a close months later when CDC scientist Joseph McDade reviewed the samples and found a tiny, round-shaped bacterium living in the lung tissue of the victims. The bacteria would be named Legionella pneumophila.  Investigators traced the bacteria back to the hotel's cooling towers. Cooling towers are essentially giant evaporative coolers and can create a mist. Legionella can thrive in the warm water of cooling towers, and the cooling towers dispersed the mist throughout the area, making hundreds ill. When water stagnates, bacteria can fester, but temperature is just as important as movement. As contractors, our maintenance procedures can save lives. In cooling towers, that maintenance entails regular cleaning, chemical treatment, and monitoring water temperature and flow.   Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool. Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium. Subscribe to our podcast on your iPhone or Android. Subscribe to our YouTube channel. Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android