Convert therm to terawatt hour

The watt (W) is a unit of power, the rate at which energy is used or produced. The watt-hour (Wh) is a unit of energy, one watt sustained for one hour, and is what this page converts: a 2 kW heater running for 3 hours uses 6 kWh, and an electricity bill counts kWh. 'Watts per hour' (W/h) would be a rate of change of power, is rarely needed, and is not the same thing as a watt-hour.

The British thermal unit, the heat that warms a pound of water by one degree Fahrenheit (1,055 J), is now mostly an American unit. US gas bills are in therms of 100,000 Btu (29.3 kWh), wholesale gas is priced per million Btu (MMBtu), and national energy statistics are in quads, 10¹⁵ Btu: the US uses about 100 quads a year. The ton-hour is the cooling delivered by one refrigeration ton over an hour, 12,000 Btu.