Glossary
Home electrification glossary
Every contractor uses jargon. Every quote has acronyms. This page translates the 30 most common ones plainly. Bookmark it — you'll want it open while reading bids.
Tax credits & rebates
- 25C credit (Energy Efficient Home Improvement Credit)
- Federal tax credit covering 30% of cost for qualifying heat pumps, heat pump water heaters, electrical panels, insulation, and windows. Annual category caps apply ($2,000 for heat pumps and HPWHs combined; $600 for panels). Through Dec 31, 2025 under current law.
- 30C credit (Alternative Fuel Vehicle Refueling Property Credit)
- Federal tax credit covering 30% of cost (up to $1,000) for residential EV chargers and other alt-fuel refueling equipment. Limited to qualifying census tracts; check the AFDC tract-lookup tool. Property placed in service through June 30, 2026.
- HEEHRA (High-Efficiency Electric Home Rebate Act)
- One half of the federal DOE Home Energy Rebates program, providing point-of-sale rebates for income-qualified households on heat pumps, water heaters, electrical panels, wiring, and more. Rolling out by state through 2031.
- HOMES Rebate Program (Home Owner Managing Energy Savings)
- The performance-based half of the DOE Home Energy Rebates: pays based on whole-home modeled or measured energy savings. Like HEEHRA, administered by states with varying timelines.
Electrical & panels
- Amps (panel size) (Amperes)
- The current-carrying capacity of your home's electrical service. 100A is common in older homes, 200A in newer ones, 320/400A in larger or all-electric homes. Heat pumps and EV chargers may need a panel upgrade if your service is undersized.
- NEC 220.83
- Section of the National Electrical Code that defines how to compute the existing load on a service before adding new circuits. The basis for deciding whether your panel can handle a heat pump or EV charger without an upgrade.
- NEMA 14-50
- A 240V/50A outlet — the same one used by RV parks. Common choice for plug-in Level 2 EV chargers and some induction ranges. Hardwiring is required for ≥48A continuous-load chargers.
- Service drop / service entrance
- The wires running from the utility's pole or transformer to your home's meter. Service-upgrade jobs often include replacing this run, especially when going from 100A to 200A or higher.
- Smart load management
- A device or panel that intelligently schedules large electric loads (EV charger, heat pump, dryer) so the home never exceeds the existing service capacity. Can substitute for a panel upgrade in many homes. NEC 750-listed devices are typical.
- Subpanel
- A secondary breaker panel fed from the main panel. Useful for a garage, addition, or to free space in a full main panel. Cheaper than a full main-panel upgrade but doesn't increase total service capacity.
Heating & cooling
- AFUE (Annual Fuel Utilization Efficiency)
- Percentage of fuel a furnace converts into useful heat over a year. An 80% AFUE furnace turns 80 cents of every fuel dollar into heat; the rest goes up the flue. Modern condensing furnaces hit 95%+.
- COP (Coefficient of Performance)
- Ratio of heat delivered to electrical energy consumed. A heat pump with COP 3.0 delivers 3 units of heat for every 1 unit of electricity. Electric resistance heaters have COP 1.0; cold-climate heat pumps maintain COP ~2 even at 5°F.
- Dual-fuel system
- A heat pump paired with a gas or oil furnace. The heat pump runs in mild weather (where it's most efficient); the furnace kicks in for very cold conditions. Common in cold climates as a way to keep existing fuel infrastructure as backup.
- Ducted heat pump
- A central heat pump that uses your home's existing ductwork to distribute heated/cooled air. Replaces a furnace or AC. Cheaper to install than a multi-zone ductless system if ducts are usable.
- Ductless mini-split
- A heat pump that pairs an outdoor unit with one or more wall-mounted indoor heads. Each head is its own zone, useful for additions, garages, or homes without ducts. Multi-zone systems can be more expensive than ducted.
- HSPF / HSPF2 (Heating Seasonal Performance Factor)
- Heat pump heating efficiency measure. Higher is better. HSPF2 is the newer test standard (2023+) and gives slightly lower numbers than the legacy HSPF for the same equipment. ENERGY STAR certified heat pumps usually have HSPF2 ≥ 7.5.
- Manual J
- ACCA's residential heating and cooling load-calculation method. The industry standard for sizing HVAC equipment. If a contractor 'uses my old furnace size' or 'rules of thumb,' that's a red flag.
- Manual S
- ACCA's standard for selecting equipment to match the Manual J load. Sized too small and you'll be uncomfortable; sized too large and you'll cycle and lose efficiency and humidity control.
- Rated capacity at 5°F
- How many BTU/hr of heat a heat pump produces at 5°F outdoor temperature. The single best number to look at for cold-climate performance. NEEP's database publishes this for hundreds of models.
Water heating
- HPWH (Heat Pump Water Heater)
- A water heater that uses a heat pump to move heat from surrounding air into the tank, instead of generating heat directly. Typically 2–3× more efficient than electric resistance; comes in 120V plug-in and 240V hybrid models.
- UEF (Uniform Energy Factor)
- Water-heater efficiency metric (replaces older 'EF'). Higher is better. ENERGY STAR HPWHs typically have UEF 3.0+; gas water heaters are around 0.6–0.7.
Kitchen
- Induction cooktop
- An electric cooktop that uses an electromagnetic field to heat ferrous (magnetic) cookware directly — the surface stays cool. Faster, more responsive, and more efficient than gas or electric resistance.
EV charging
- EVSE (Electric Vehicle Supply Equipment)
- The technical name for a 'charger' — actually, the wall-mounted unit, cable, and connector that delivers power to your EV. Level 1 = 120V, Level 2 = 240V, DC fast charging = high-voltage commercial.
General
- BTU (British Thermal Unit)
- The amount of energy needed to raise 1 lb of water by 1°F. HVAC equipment is sized in BTU/hr; 12,000 BTU/hr = 1 ton of cooling.
- HDD (Heating Degree Days)
- A weather metric that quantifies how cold a location is. The number of degrees by which the average daily temperature falls below 65°F, summed over the year. Boston ≈ 6,000 HDD, Houston ≈ 1,400. Higher = more heating needed.
- IECC climate zone (International Energy Conservation Code climate zone)
- A standardized 1–8 climate-zone system used by U.S. building codes. Zone 1 is South Florida; Zone 7–8 is Alaska. Determines insulation requirements, equipment-sizing assumptions, and whether cold-climate-rated heat pumps are recommended.
- kWh (Kilowatt-hour)
- The unit your utility bills you in for electricity. 1,000 watts of power for one hour. A typical U.S. home uses 800–1,200 kWh/month.
- Load calculation
- The math an HVAC contractor (Manual J) or electrician (NEC 220.83) does to figure out how much heat/cool or how much amperage your home actually needs. A right-sized heat pump or panel comes from a real load calc — not from a tape measure or rule of thumb.
- Therm
- 100,000 BTU of natural-gas energy. The unit on your gas bill. A typical U.S. household uses 30–80 therms/month for heating in winter.
- Ton (HVAC)
- 12,000 BTU/hr of heating or cooling capacity. Named after the cooling produced by melting one ton of ice in 24 hours. A 3-ton heat pump = 36,000 BTU/hr.
Spotted something we should add or correct? Sources for our definitions are catalogued on the sources page.