Glossary

The words on a bill, a quote and a program page, in plain English.

Air sealing

Closing the gaps where air leaks in and out of a home (attic hatch, rim joist, penetrations, recessed lights). Usually the cheapest effective measure.

Baseload

The energy a home uses every day regardless of weather: water heating, refrigeration, electronics, pumps.

Blower door

A fan fitted in a doorway that depressurises the house to measure and locate air leaks.

BTU

British thermal unit, a unit of heat. Heating and cooling equipment is sized in BTUs per hour.

CCF / therm

Gas volume and gas energy units on a bill. One CCF is roughly one therm.

COP

Coefficient of performance: heat delivered divided by electricity used. A heat pump with a COP of 3 delivers three units of heat per unit of electricity.

Design temperature

The coldest (or hottest) outdoor temperature a system is sized for in your location.

Duct leakage

Conditioned air lost from ducts that run through attics, crawlspaces or garages. Often large and often fixable.

Energy assessment / audit

A professional inspection of how a home uses and loses energy, usually with a blower door and infrared camera, ending in a prioritised report.

Envelope

The parts of a house that separate inside from outside: walls, roof, floor, windows, doors.

Heat pump

Equipment that moves heat rather than making it. Heats and cools; available as ducted, ductless and water-heater versions.

HSPF2 / SEER2

Current efficiency ratings for heat pumps and air conditioners: heating season (HSPF2) and cooling season (SEER2). Higher is more efficient.

kWh

Kilowatt-hour: the unit of electricity on your bill. One kWh runs a 100-watt bulb for ten hours.

Load calculation (Manual J)

The engineering method for sizing heating and cooling equipment to a specific house.

Pre-approval

A program's confirmation, before work starts, that a project and contractor are eligible. Often required.

R-value

Insulation's resistance to heat flow. Higher is better; the attic usually needs the highest.

Rebate

A payment or discount from a utility, state program, manufacturer or retailer for qualifying equipment or work. Terms vary by program and change over time.

Setback

Lowering the thermostat while you sleep or are out. Saves energy in most homes; use small setbacks with a heat pump.

Stacking

Combining more than one program on the same project. Allowed by some programs, excluded by others.

Tax credit (25C / 25D)

The federal residential energy tax credits, which ended for work placed in service after December 31, 2025.

Weatherstripping

Flexible seals on doors and operable windows that stop drafts.