Therm
A unit of heat equal to 100,000 BTU (105.5 MJ, 29.307 kWh), used for billing natural gas to homes and businesses in the US and formerly the UK.
The therm is a convenient retail-sized unit of gas energy. US utilities bill residential customers in therms or in hundreds of cubic feet (Ccf) converted with a heat-content factor; the UK billed gas in therms until the 1990s and still uses them in some wholesale contracts (NBP prices quoted in pence per therm).
1 MMBtu = 10 therms; 1 dekatherm (Dth) = 10 therms = 1 MMBtu
1 Ccf (100 ft³) of natural gas ≈ 1.036 therms (US average heat content)
1 kWh = 0.03412 therm
Price conversion: USD/therm x 34.12 = USD/MWh; UK p/therm x 0.3412 = GBP/MWh
Typical US residential gas prices have been roughly 1.2–1.8 USD per therm in recent years (EIA), equivalent to about 4–6 US cents per kWh of heat content. Comparing with a heat pump: if electricity costs 16 cents/kWh and the heat pump has a seasonal COP of 3, heat costs about 5.3 cents/kWh; a 90% efficient furnace burning gas at 1.50 USD/therm delivers heat at about 5.7 cents/kWh.
A typical US gas-heated home uses roughly 500–1,000 therms per year, depending on climate (heating degree days) and insulation. See also BTU and MMBtu.
Related terms
All terms →- BTU (British thermal unit)
A traditional unit of heat, approximately the energy needed to raise one pound of water by one degree Fahrenheit; 1 BTU (IT) = 1,055.06 J.
- MMBtu
One million British thermal units (1.05506 GJ, 293.07 kWh); the standard pricing unit for natural gas and LNG in the United States and Asia.
- Natural gas
A fossil fuel composed mainly of methane, used for power generation, industrial and residential heat, and as a chemical feedstock for hydrogen and ammonia.
- Kilowatt-hour (kWh)
A unit of energy equal to one kilowatt of power sustained for one hour, or 3.6 megajoules; the standard billing unit for electricity.
- Heat pump
A device that uses a refrigeration cycle to move heat from a cooler source (air, ground, water) to a warmer sink, delivering 2–5 units of heat per unit of electricity.