This glossary covers terms you'll see across our hvac content, contractor quotes, manufacturer spec sheets, and incentive program documentation. Use it as a reference - we link key terms from across the site back to definitions here.
- HVAC
- Heating, Ventilation, and Air Conditioning. Umbrella term for all home climate systems.
- BTU (British Thermal Unit)
- Unit of heat energy. AC and furnace capacity measured in BTU/hr (often shortened to BTU).
- Ton (Cooling)
- 12,000 BTU/hr of cooling. A 3-ton AC = 36,000 BTU/hr. Typical home: 2-5 tons.
- SEER / SEER2
- Seasonal Energy Efficiency Ratio. Higher = more efficient. Federal minimum is 14-15 SEER2 depending on region.
- AFUE
- Annual Fuel Utilization Efficiency. Percentage of fuel converted to usable heat. Federal minimum 80%; high-efficiency 90-97%.
- HSPF / HSPF2
- Heating Seasonal Performance Factor. Measure of heat pump heating efficiency.
- COP (Coefficient of Performance)
- Heat pump efficiency at a specific temperature. COP of 3.0 means 3 units of heat per unit of electricity.
- Heat Pump
- Refrigerant-cycle system that provides both heating and cooling. Increasingly replaces gas furnace + AC.
- Mini-Split (Ductless)
- Heat pump with one outdoor unit and one or more indoor heads. No ductwork required.
- Air Handler
- Indoor unit that moves conditioned air through ductwork. Used with AC and heat pumps.
- Furnace
- Indoor unit that burns gas/propane/oil or uses electric resistance to heat air.
- Refrigerant
- Working fluid in AC and heat pump systems. R-410A is being phased out for R-454B / R-32.
- Ductwork
- Metal or flex tubing that distributes conditioned air. Quality and sealing dramatically affect efficiency.
- Static Pressure
- Pressure in ductwork. Excessive static = blocked filter, undersized ducts, or closed registers.
- Manual J Load Calculation
- Industry-standard heat loss/gain calculation to properly size HVAC equipment.
- Two-Stage / Variable Speed
- Compressor or blower that runs at multiple speeds rather than just on/off. More efficient and quieter.
- Variable Refrigerant Flow (VRF)
- Commercial heat pump system that varies refrigerant flow to multiple zones simultaneously.
- Cold-Climate Heat Pump
- Heat pump designed for sub-zero performance. Rated to -15F or colder.
- Backup Heat (Auxiliary Heat)
- Electric resistance or gas heating that supplements a heat pump in extreme cold.
- Programmable Thermostat
- Schedules temperature setbacks. Smart thermostats (Nest, Ecobee) add learning and remote control.
- MERV Rating
- Air filter efficiency. MERV 8-13 typical for residential. Higher = better filtration but higher static pressure.
- Heat Recovery Ventilator (HRV/ERV)
- Mechanical ventilation that pre-conditions incoming fresh air using outgoing exhaust heat.
- Indoor Air Quality (IAQ)
- Comprehensive air quality including humidity, VOCs, particulates, and CO2 levels.
- 25C Tax Credit (Energy Efficient Home Improvement)
- Federal credit covering 30% of qualifying HVAC upgrades. $2,000 cap for heat pumps.
- Energy Star Certified
- Qualified efficient equipment eligible for federal credits and utility rebates.