Making sense of all the terminology used in reference to a home heating system isn’t easy. One term you’ve probably heard many times is “BTU.” If you’d like to know exactly what it means and the role it plays when you’re choosing a furnace or heat pump, here’s a brief primer that can help clarify the topic.
BTU is short for “British thermal unit,” but it’s not a term related to heating systems in the U.K. Here in the U.S., it’s used as a measurement of heat energy, with one BTU being the amount of energy used to heat a pound of water by one degree. To help you gauge how much energy that is, one BTU is produced when you completely burn a 4-inch wooden match stick.
Home Heating Equipment and BTUs
When you’re comparing heating equipment like furnaces and heat pumps, you’ll probably notice that they have two BTUs listed. The first number is the input, which is the amount of fuel the unit burns. The second number is the output, or the usable heat the unit generates. When you’re looking at specific models, the input number tells you the capacity or size, while the output number tells you how efficiently they operate.
How Many BTUs Should Your Heating Equipment Have?
Furnaces and heat pumps are available with input BTUs ranging from 40,000 up to 100,000. When you’re selecting new equipment, it’s may seem logical that a bigger capacity is better, but that’s not true. Equipment will short cycle if it’s oversized for your living space, making it too hot when it cycles on and too chilly when it cycles off.
To size equipment correctly for your home, an HVAC contractor needs to do a Manual J calculation based on specific conditions like your:
- Square footage.
- Size/type of windows.
- Amount/type of insulation.
- Ductwork design.
- Local climate.
With the equipment capacity calculated, a pro can recommend specific models based on their efficiency ratings.