Learning Center · Glossary
HVAC glossary
Plain-language definitions for the heating, cooling, and code terms used across this site — so you can make decisions without the jargon.
Common HVAC terms, explained
Use these definitions while comparing heating, cooling, indoor air, and permit decisions for your Monee-area home.
- AFUE
- Annual Fuel Utilization Efficiency — the percentage of fuel a furnace or boiler turns into usable heat over a year. A 96% AFUE furnace wastes only 4% of its fuel. Explore AFUE in context
- SEER2
- Seasonal Energy Efficiency Ratio 2 — the current standard rating for air-conditioner and heat-pump cooling efficiency. Higher is more efficient. Explore SEER2 in context
- HSPF2
- Heating Seasonal Performance Factor 2 — the standard rating for heat-pump heating efficiency. Higher means more heat per unit of electricity. Explore HSPF2 in context
- BTU
- British Thermal Unit — the basic measure of heating or cooling energy. HVAC capacity is rated in BTUs per hour.
- Ton (of cooling)
- A unit of AC capacity equal to 12,000 BTU/hr. Residential systems are commonly 1.5 to 5 tons, sized to the home, not guessed. Explore Ton (of cooling) in context
- Heat exchanger
- The metal component that transfers combustion heat to your home's air (furnace) or water (boiler) without mixing exhaust with what you breathe. A cracked one means replacement. Explore Heat exchanger in context
- Compressor
- The pump at the heart of an AC or heat pump that pressurizes refrigerant so it can release absorbed heat. The most expensive part to replace. Explore Compressor in context
- Evaporator coil
- The indoor coil where refrigerant absorbs heat from your home's air, cooling it. Explore Evaporator coil in context
- Condenser
- The outdoor unit that releases the heat collected indoors, using a coil, fan, and compressor. Explore Condenser in context
- Refrigerant (R-410A / R-454B)
- The fluid that carries heat through an AC or heat pump. R-454B is the current low-GWP standard for new systems; R-410A is being phased down, which affects repair-vs-replace decisions. Explore Refrigerant (R-410A / R-454B) in context
- Heat pump
- A system that moves heat rather than burning fuel — cooling in summer and heating in winter by running the refrigerant cycle in reverse. Explore Heat pump in context
- Ductless mini-split
- A heat pump that conditions individual rooms through wall or ceiling units, with no ductwork — ideal for additions and zoning. Explore Ductless mini-split in context
- Hydronic heating
- Heating that uses hot water circulated through radiators, baseboards, or floor tubing instead of blown air. Explore Hydronic heating in context
- Boiler
- Equipment that heats water (or makes steam) for hydronic heating. Common in older homes and a Five Sons specialty. Explore Boiler in context
- Circulator pump
- The pump that moves heated water through a hydronic loop to radiators or baseboards and back to the boiler. Explore Circulator pump in context
- MERV
- Minimum Efficiency Reporting Value — an air-filter rating. Higher captures finer particles, but too high for your system restricts airflow. Explore MERV in context
- Static pressure
- The resistance the blower pushes against in the duct system. High static pressure (from leaks, undersizing, or restrictive filters) hurts comfort and equipment life. Explore Static pressure in context
- Load calculation (Manual J)
- An engineering calculation of a home's true heating and cooling needs, used to size equipment correctly instead of copying the old unit. Explore Load calculation (Manual J) in context
- Tankless water heater
- A water heater that heats water on demand as it flows, providing endless hot water within its flow-rate limit, with no storage tank. Explore Tankless water heater in context
- C-wire
- The common wire that supplies continuous power to many smart thermostats. Missing C-wires cause dropouts and require an adapter or new wiring. Explore C-wire in context
- AHJ
- Authority Having Jurisdiction — the local building department or official that issues permits and enforces code where the work is done. Explore AHJ in context
- Permit & inspection
- Municipal authorization to perform regulated work, followed by an inspection confirming it meets the adopted code. Required for most HVAC changeouts. Explore Permit & inspection in context
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