Btu (15.8°C, Canada)
The Btu (15.8°C, Canada) is a variant of the British thermal unit defined as the energy to raise the temperature of one pound of water by one degree Fahrenheit at a starting temperature of 15.8°C. This definition is tailored to Canadian standards reflecting the country's historical reliance on both imperial and metric.
Btu (I.T.)
The British thermal unit (International Table), Btu (IT), is about 1,055 joules, roughly the energy needed to warm one pound of water by one degree Fahrenheit. In the United States air conditioners and furnaces are rated in Btu per hour.