Understanding BTUs
When shopping for appliances, one of the first things you'll notice is a unit known as BTU. So, what exactly are BTUs, and why are they so important for fireplaces and other energy-consuming devices? BTU is an energy measurement that stands for British Thermal Unit. It refers to the amount of energy required to raise one pound of water one degree Fahrenheit.

Because the stored energy in the fuel is frequently converted into heat by the fireplace or furnace, BTU can also assist you in determining heating capabilities. When dealing with air conditioners, the energy is used to remove the heat from the room. In that case, BTU stands for cooling capacity.

Why Are BTUs Used? For hundreds of years, BTUs have been used to measure energy and are a common unit in the heating and cooling industry. It also allows you to compare various types of fuel. For example, you can compare energy sources by converting the energy in electricity, propane, natural gas, or wood into BTUs.

Surprisingly, BTU is a very small unit used to measure the output of household appliances. In 2018, the United States consumed approximately 101.3 quadrillion BTUs of energy. That's 1,000,000,000,000,000.
This is why BTU numbers are frequently written with a "K" to indicate "thousand." As a result, rather than listing the heater as having an output of 80,000 BTUs, it could simply be rated at 80K BTUs. Another way to avoid listing all those zeroes is to introduce a completely new unit. The price of propane gas is determined by the therm. A therm is equivalent to 100,000 BTUs.

What Is Efficiency, and How Does It Affect BTUs?

Efficiency is determined by the ratio of BTU input to BTU output. In an ideal world, your fireplace would convert 10,000 BTUs of fuel into 10,000 BTUs of useful heat. That, as you might expect, is not how it works. This is where effectiveness comes into play. Manufacturers rate the amount of fuel energy that is converted into output by listing a percentage.

A heater with a BTU input of 80,000 and a 65% efficiency rating, for example, will produce 52,000 BTUs. In terms of fuel or electricity, this means that the heater consumes 80,000 BTU but only produces 52,000 BTU of heat to warm your home.


Hopefully, you're now up to speed on the most popular unit among fireplace manufacturers. The fact that BTU is a standard unit across many different types of fuels and appliances makes comparing the various outputs much easier. Keep an eye out for the difference between the BTU input and the BTU output that has been adjusted for the efficiency of the appliance.