HVAC School - For Techs, By Techs

In this informative episode, host Bryan welcomes guest Bert for an in-depth discussion on the often-overlooked but critically important topic of electric heat in HVAC systems. The conversation takes listeners through both the common and uncommon issues that arise with electric heat installations, offering practical insights drawn from years of field experience. Bryan and Bert balance technical expertise with relatable storytelling, making complex electrical concepts accessible to both HVAC professionals and homeowners interested in understanding their heating systems. The discussion begins with some of the more dramatic (and rare) scenarios, including tales of objects left on heat strips during installation—from instruction manuals to spray glue cans—that have led to fires and property damage. These cautionary tales serve as memorable reminders of the importance of proper installation practices. The conversation then shifts to the far more common issues technicians encounter regularly, particularly loose electrical connections. With electric heat strips drawing substantial continuous amperage—often 20 amps per 5kW or more—poor connections can quickly lead to melted wire nuts, damaged terminal blocks, and potentially dangerous situations. Bryan and Bert emphasize that these connection problems often don't manifest until the heating season begins, making proper installation and inspection critical. Bryan and Bert also address widespread confusion around emergency heat versus auxiliary heat, explaining why emergency heat settings are largely obsolete in most modern heat pump applications. They clarify that in typical residential installations with 5-10kW heat strips, the electric backup cannot efficiently heat an entire home on its own, making the emergency heat function impractical. Instead, auxiliary heat should work in tandem with the heat pump to supplement heating during extremely cold conditions or defrost cycles. The hosts advocate for implementing lockout controls that prevent auxiliary heat from activating unless outdoor temperatures drop below 40 degrees, helping homeowners avoid unnecessarily high electricity bills while still maintaining comfort. The technical discussion extends to critical safety mechanisms, including interlocks, thermal overloads, and fusible links that prevent catastrophic failures. Bryan provides historical context on how interlock systems have evolved from high-voltage relay-based designs to modern control board logic, while warning against improper retrofitting that can create new hazards. The episode concludes with practical guidance on proper sizing, voltage considerations, airflow requirements, and the economics of electric heat versus other fuel sources. Throughout the conversation, Bryan and his guest stress that while electric heat is simple and reliable, it demands respect for proper electrical practices and thoughtful system design to ensure both safety and cost-effectiveness. Topics Covered Installation Horror Stories and Safety Hazards: Objects left on heat strips causing fires, including the infamous spray glue can incident Loose Electrical Connections: The #1 issue with electric heat systems and why continuous high amperage makes proper connections critical Wire Sizing and Breaker Matching: Common mistakes when replacing furnaces with heat pumps and the dangers of undersized wiring Emergency Heat vs. Auxiliary Heat: Why emergency heat is largely obsolete in modern residential applications and when auxiliary heat should actually engage Heat Output Calculations: Understanding BTU production per kilowatt (3.41 BTUs per watt) and why 5-10kW strips can't heat most homes alone Lockout Controls and Outdoor Thermostats: Implementing temperature-based restrictions to prevent unnecessary auxiliary heat operation above 40°F Interlock Systems Evolution: How blower/heat strip safety interlocks have changed from relay-based to control board logic Thermal Overloads and Fusible Links: The two types of safety devices that prevent overheating and fire hazards Defrost Cycle Operation: How auxiliary heat integrates with heat pump defrost sequences Balance Point and Dual Fuel Considerations: Economic and operational factors in choosing between electric and gas backup heat Voltage Variations and Sizing: Working with different voltage ratings (208V vs. 240V) and how they affect heat output Diagnostic Techniques: Using Ohm's law and resistance measurements to verify heat strip operation and specifications Airflow Requirements: Why proper air movement is critical for preventing overload trips and premature failures Electrical Safety Practices: Avoiding dangerous shortcuts like bypassing thermal limits or using undersized relays Energy Efficiency and Economics: Comparing the true cost-effectiveness of electric heat versus gas and heat pump operation   Have a question that you want us to answer on the podcast? 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