Hot Tip #25 – Unit of thermodynamic energy

The British thermal unit (BTU or Btu) is a unit of energy equal to about 1.06 kilojoules.

It is the amount of energy needed to heat one pound of water one degree Fahrenheit.

Engineers use MMBTU to represent one million (106) BTUs.

A Therm is used to represent 100,000 (105) BTUs.


One boiler horsepower is equal to 33,479 BTUs per hour.

One cubic foot of natural gas is about equal to 980 BTUs.

A 400-pound dryer will have a maximum burner rating of about 25 Therms per hour.

A gallon of diesel fuel has about 138,700 BTUs per US gallon.

A gallon of regular gasoline has about 125,000 BTUs per US gallon.

To heat a small (10,000 gallon) swimming pool from 58 F. to 78 F. requires:

10,000 gallons * 8.34 pounds/gallon * 20 degrees =   1,668,000 BTU’s