Home energy calculators

Energy jargon decoder

22 terms

• AFUE

  Annual Fuel Utilization Efficiency: the share of a furnace's or boiler's fuel that becomes heat over a year. A 95% AFUE furnace turns 95 cents of every fuel dollar into heat.

• Air sealing

  Closing gaps and cracks that let outside air leak in and conditioned air leak out, usually with caulk, foam and weatherstripping. Usually done before adding insulation.

• AMI

  Area Median Income: the middle household income for your area. Many rebate programs set income limits as a percentage of AMI, such as 80% or 150%.

• Blower door test

  A test where a fan in a doorway depressurizes the house so an auditor can measure and find air leaks.

• BTU

  British thermal unit: the heat needed to warm one pound of water by 1°F. Heating and cooling equipment is sized in BTU per hour.

• COP

  Coefficient of performance: units of heat delivered per unit of electricity used. A COP of 3 means three times as much heat as electric resistance.

• Degree days (HDD)

  Heating degree days add up how far each day's average temperature falls below 65°F. More degree days means more heating needed.

• Energy burden

  The share of household income spent on home energy bills. Above about 6% is commonly called high.

• Heat pump

  An electric system that moves heat instead of making it: out of the house in summer and into the house in winter.

• HEEHR / HEAR

  High-Efficiency Electric Home Rebate program, a state-run federal rebate capped at $14,000 per household for low- and moderate-income homes. Only live in some states.

• HOMES

  Home Owner Managing Energy Savings rebates: state-run, whole-home rebates paid for measured or modeled energy savings, up to $8,000 federally.

• HSPF2

  Heating Seasonal Performance Factor (2023 test): a heat pump's heating efficiency in BTU per watt-hour. ENERGY STAR split systems need 7.8 or more.

• kWh

  Kilowatt-hour: the unit on your electric bill. A 1,000-watt appliance running for one hour uses 1 kWh.

• LIHEAP

  Low Income Home Energy Assistance Program: federal money, run by states and local agencies, that helps eligible households pay heating and cooling bills.

• Manual J

  The industry standard load calculation for sizing heating and cooling equipment room by room. Ask contractors whether they did one.

• R-value

  How well insulation resists heat flow. Higher is better. Attics in most of the US should reach R-49 to R-60.

• SEER2

  Seasonal Energy Efficiency Ratio (2023 test): cooling efficiency of an air conditioner or heat pump. Higher means less electricity for the same cooling.

• SHGC

  Solar Heat Gain Coefficient: how much of the sun's heat a window lets in, from 0 to 1. Lower is better in hot climates.

• Therm

  A unit of natural gas energy equal to 100,000 BTU. Many gas bills charge per therm.

• U-factor

  How fast a window or door loses heat. Lower is better. Find it on the NFRC label.

• UEF

  Uniform Energy Factor: a water heater's efficiency rating. Gas tanks are around 0.6–0.7; heat pump water heaters are often 3 or higher.

• Weatherization (WAP)

  The federal Weatherization Assistance Program provides free energy upgrades for income-eligible households, generally up to 200% of the poverty guidelines.

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