What BTU Furnace Do I Need For My Home?

What Is BTU? 

The abbreviation BTU stands for British Thermal Unit. This is a unit of heat traditionally used to measure the amount of heat output given by a heating system. To determine the proper BTU you’ll need for your home’s heating, you’ll have to do a little math.

To calculate your BTU needed, you simply need to know your climate region and the square footage of your home.


Simply reference the map and find your climate zone and take the BTUs per square foot for your climate zone times the square footage of your home.

For example:
Let's say you live in a 1500 square foot home northern Ohio, which is climate zone 4.
Take your square footage (1500) times your zones BTU per square feet.
1500x50= 75,000 BTU

What happens if I buy the wrong size furnace?

Buying a furnace that is too small for your home means your furnace will not be capable of keeping your home warm during the coldest days. It will be running constantly, but if it is too small for your home it will never shut off and it will just get colder and colder in your home as the furnace is incapable of keeping up with the cold temps outside. This will cause your furnace to break down prematurely.

When you purchase a furnace that is too large for your home, you will see wide variations of heating. Your home will heat too quickly and be very hot, then feel very cold and keep repeating this cycle. This will also cause your furnace to short cycle. Short cycling means it will kick on and off too quickly. A furnace that is too large will not run long enough to move air to the furthest rooms in your house before it satisfies the thermostat and shuts off.

A humidifier that is connected to a furnace that short cycles will not run long enough to properly humidify the home, which can cause dry, itchy skin and static shocks.

There will be additional noise with a furnace that is too large for the duct system in your home. An oversized furnace will not just have “too large” burners in it, it will also have a “too large” blower in it. The oversized blower in the oversized furnace will move too much air through the ducts which creates a lot of air noise at your vents. Have you ever had to turn the volume up on your TV when the furnace comes on? A properly sized furnace can alleviate that by not forcing too much air through your duct system, which as mentioned, creates lots of noise.

An oversized furnace with an air cleaner, high efficiency filter, or electronic air cleaner will shut down before it has a chance to properly clean the air in your home. This also causes your furnace to use much more fuel than it should, thus your utility bills will increase.

Use our sizing guide here.