HVAC School - For Techs, By Techs

In this short podcast episode, Bryan talks about some building science concepts, including vapor diffusion ports, hygric buoyancy, and... fruit packaging?
Much of building science wisdom over the past couple of decades has dealt with air sealing (just seal it tighter!). However, building tightness has a darker side: more difficulty drying. When buildings can't dry, moisture accumulates and leads to rot.
Air leaks and vapor diffusion are NOT the same thing. Vapor diffusion refers to water vapor diffusing through surfaces into the home (through the materials of walls, floors, etc.). Air moves much more water than vapor diffusion, so air leaks are a bigger problem in terms of moisture. Therefore, air barriers matter more than vapor barriers... until the air barrier battle has been won.
Hygric buoyancy refers to moist air's lower density than dry air, so wet air rises toward the attic (and then the attic peaks). While sealed attics are excellent, moisture can accumulate at the roof deck, especially when the roofing cools at night. The condensation is worsened by using open-cell foam, as open-cell foam is air-closed but vapor-open (whereas closed-cell foam is air-closed AND vapor-closed). Drying isn't needed if you can KEEP the moisture out of closed-cell foam. Open-cell foam requires a place for vapor to go.
Vapor diffusion ports are airtight, controlled vapor-open outlets at the highest points of sealed attics. A cap protects them from bulk water, and they consist of a membrane that blocks air but allows vapor to exit. Unlike a ridge vent, ventilation is not the goal of a vapor diffusion port; it is drying by diffusion rather than airflow and acts as a controlled pressure-relief valve for moisture. Vapor diffusion ports have been proven to be effective at drying and preventing roof rot in humid climates (but NOT ALL climates). They do not work against bulk water intrusion, in cold climates, or when used as vents. Vapor diffusion ports work like fruit packaging, which is designed to let oxygen in and CO2 out, while controlling moisture and slowing decay.
 
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In this informative episode, Bryan and Bert dive deep into gas appliance safety and combustion analysis from the unique perspective of Florida HVAC technicians. While they humorously acknowledge that Florida's mild winters mean they don't work on gas furnaces daily, they make a compelling case that this actually makes their training even more critical. When technicians only encounter gas appliances occasionally, the stakes are higher—which is why they've developed rigorous protocols to ensure safety every single time.
The conversation covers everything from the basics of gas leak detection to the nuances of carbon monoxide monitoring, combustion air zones, and proper venting. Bryan and Bert share real-world stories of dangerous situations they've encountered, from exploding pool heaters to improperly capped gas lines at vacation rentals. Their approach emphasizes that every gas leak is your problem when you're on site, regardless of why you were originally called out. This episode is packed with practical wisdom for both seasoned professionals working in gas-heavy markets and those who encounter these systems less frequently.
Throughout the discussion, the hosts stress fundamental safety principles that apply across all markets: using your nose to detect leaks, understanding the difference between unspent gas and carbon monoxide, ensuring proper combustion air zones, and never ignoring warning signs like delayed ignition or flame rollout. They also tackle common misconceptions about equipment like flexible gas connectors, orphaned water heaters, and the real risks of cracked heat exchangers. 
The conversation wraps up with important reminders about company lockout/tagout procedures, the critical importance of low-level carbon monoxide detectors, and the tools every technician should carry. Bryan and Bert's candid, no-nonsense approach makes complex safety topics accessible while never losing sight of how serious the consequences can be when gas work goes wrong.
Topics Covered
Gas leak detection and response protocols - Why every gas leak on site becomes your responsibility, using your nose as the first line of defense, and never leaving a leak for someone else to fix
Carbon monoxide safety and monitoring - Understanding CO as a combustion byproduct, the limitations of standard UL-rated detectors, and the critical importance of low-level CO monitors
Combustion air zones and depressurization - Identifying risks from sealed spaces, return air leaks, exhaust fans, and other equipment that can create dangerous negative pressure
Delayed ignition and flame rollout - Recognizing warning signs, understanding causes, and why you should never ignore scorched wires or tripped rollout switches
Proper gas line assembly and materials - Selecting appropriate materials for different environments, avoiding flexible connector failures, and ensuring proper sizing
Combustion analysis fundamentals - Measuring CO levels in the flue, targeting air-free CO under 100 ppm, and understanding when adjustments are needed
Natural draft vs. induced draft systems - Differences in safety considerations, orphaned water heaters, and the myth of oversized flue pipes
Venting requirements and back drafting - Identifying improper venting, looking for evidence of back draft on water heaters, and ensuring proper flue design
Gas pressure testing and adjustment - When to adjust and when not to, reading data tags, and understanding that most flame problems are air-related, not gas pressure
Cracked heat exchangers in context - Why they're less common in warm climates, the role of proper airflow, and focusing on actual safety risks vs. edge cases
Tools and equipment recommendations - Combustion analyzers, personal protective CO detectors, combustible gas detectors, precision manometers, and low-level CO alarms
Lockout/tagout procedures - Following company protocols, communicating clearly with customers, and balancing safety requirements with homeowner autonomy
 
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 dives a bit into equipment sizing rules of thumb and why square footage does NOT equal tonnage in today's world. Many rules of thumb exist in the industry, and one is a load calculation rule stating that you can size the HVAC for a house at 500 square feet per ton. 
Old houses are leaky and poorly insulated compared to new homes, which results in large energy loads but allows the homes to dry themselves out, as moisture could leak out before it could cause trouble indoors. Large loads and leaky envelopes made 500-600 square feet per ton a sensible rule. 
Homes built within the last few decades have a lot more insulation and are tighter, and they have smaller sensible heat loads. However, they're a lot more moisture-prone, especially when moisture can't escape via proper ventilation paths. The 500 square-foot rule of thumb overshoots the latent capacity and leads to short cycling due to oversized equipment. Enter ACCA Manual J, which presents a load calculation method that is very good, but it has barriers to entry; it is very rigorous, has a learning curve, and can be a hassle. One thing is clear, though: load management is key, especially latent load management.
At this time, we measure energy efficiency in terms of metrics like SEER, but the future is pointing to peak load management as the answer: getting the right power draw at the right moments instead of high general efficiency. Modernizing hot deck-cold deck systems with steady-state, constantly running systems might be the way to go, especially if we utilize energy storage and modern variable-speed technologies.
The new rule of thumb is to think like a building scientist and apply new tools to concepts that have stood the test of time. Low peak loads and steady-state operation are often the way to go with high latent loads in homes built to the most recent building codes and standards.
 
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.

Matthew Taylor delivers an expert-level presentation on EPRs, building on his previous work on parallel rack systems. While his earlier content focused on the similarities between air conditioning and refrigeration, this session explores what makes commercial refrigeration unique—particularly the critical role of EPRs in maintaining optimal operating conditions across multiple evaporators running at different temperatures. This presentation was shared at the 6th Annual HVACR Training Symposium.
The discussion begins with a fundamental review of the refrigeration cycle in a typical supermarket setting, where 30 to 80 evaporators may share a common suction line. Matthew explains why EPRs are essential: when multiple cases need to operate at different temperatures (ranging from -13°F for frozen foods to 24°F for fresh products) but all connect to the same compressor rack, EPRs become the solution that makes this possible. Without them, cases would cycle on and off constantly, creating efficiency nightmares, oil management problems, and potential food safety issues.
Matthew walks through the mechanical principles of various EPR types, from the high-efficiency Sporlan SORIT valve with its pilot-operated design to the Parker A8 valve that can be installed directly in the store. He also addresses the industry's shift toward electronic EPRs, particularly the CDS modules that offer temperature-based control rather than just pressure regulation. Throughout the presentation, Matthew emphasizes practical considerations: how EPRs affect compressor staging, oil system pressure, defrost cycles, and ultimately, the core product temperatures that determine food safety. The session includes real-world troubleshooting insights and addresses common misconceptions about setting superheat on systems with EPRs.
This technical presentation provides HVAC professionals with the knowledge needed to understand, diagnose, and service EPR-equipped refrigeration systems confidently. Matthew's approach demystifies a component that many technicians find intimidating, breaking it down into understandable principles while highlighting the critical role EPRs play in modern commercial refrigeration efficiency and reliability.
Topics Covered
Basic Refrigeration Cycle in Supermarket Applications – Understanding parallel rack systems with 30-80 evaporators sharing common suction and liquid lines
Oil Management Systems – Oil separators, oil reservoirs, oil regulators, and the critical pressure differential required for proper oil flow
Compressor Staging and Capacity Control – How parallel rack compressors operate as multi-stage units to match system load efficiently
Saturated Suction Temperature (SST) – Why racks are designated by temperature (e.g., "13-degree rack" or "-13 degree rack") and how this relates to the coldest evaporator requirement
Temperature Difference (TD) Engineering – The relationship between evaporator temperature and case leaving air temperature, typically 10 degrees in traditional systems
EPR Fundamentals – Why EPRs are necessary to maintain different evaporator pressures on cases operating at various temperatures while connected to a single rack
Mechanical EPR Types – Comparison of Sporlan SORIT valves (pilot-operated, low pressure drop) versus Parker A8 valves (self-contained, higher pressure drop)
Electronic EPR Systems – Modern CDS modules and other electronic controls offering pressure control, temperature control, or hybrid approaches
System Stability and Load Management – How proper EPR settings prevent compressor hunting, reduce energy consumption, and protect oil management systems
Subcooling Requirements – Why liquid receivers eliminate natural subcooling and how mechanical subcoolers restore it before expansion devices
Core Product Temperature – The critical relationship between runtime, EPR settings, and food safety in refrigerated cases
Dual-Temperature Applications – Converting medium-temp cases to low-temp operation (like holiday turkey displays) using EPR pilot solenoids
Superheat Setting Procedures – Why EPRs must be overridden to 50-100% open position when setting TXV superheat
High Glide Refrigerants – Special considerations for setting EPRs with refrigerants that have significant difference between dew point and bubble point temperatures
Troubleshooting Philosophy – Understanding EPRs and TXVs as independent systems that don't directly affect each other due to non-critically charged liquid receiver systems
Pressure Drop Considerations – How EPR pressure losses (0.5-2 psi depending on type) affect compressor suction setpoints and energy efficiency
Electronic Control Integration – Various controller brands and approaches to managing electronic EPRs, from pressure transducers to temperature sensors and PID algorithms
 
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 covers the history of the great heating debate: furnaces vs. heat pumps or combustion vs. compression. He also gives a breakdown of each other's strengths and gives his two cents on the winner of the debate.
Fire kept humans warm for much of history, but engineers developed a way to move heat by manipulating refrigerant pressures. Early heat pumps got a bad rap because they didn't live up to the hype; they had frequent operational issues, didn't heat effectively, and were largely unable to be serviced effectively by technicians.
However, heat pumps have evolved and now outperform furnaces in many areas. Ones with COPs between 2 and 5 can be anywhere from 200-500% efficient in terms of watts in, BTUs out. They also have many safety benefits over gas furnaces, including no risk of flame rollout, carbon monoxide poisoning, and gas leaks; removing the gas meter and all its risks entirely is a possibility. 
Nevertheless, some people still insist that combustion is king due to its comfort, as furnaces' heat is more intense than that of heat pumps. Furnaces also require little electricity, making them more sensible in markets with weak or dirty electrical grids. Combustion appliances also only need to work part of the year, meaning they run fewer cycles and experience less mechanical wear over the same period of time as heat pumps (thus may have longer lifespans).
Dual fuel allows you to get the best of both worlds; it allows the heat pump to handle the cooling and most of the heating for the energy efficiency benefits, and the furnace can step in when more intense heat is needed. Ultimately, the "winner" of this debate, at least to Bryan, is the most sensible solution for energy costs, safety, comfort, and reliability; the real answer will depend on the climate, infrastructure, and other factors.
 
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.