How many BTU does a new furnace need for my house?

How many BTU does a new furnace need for my house?

There are a few factors that go into evaluating a new furnace and the BTU number is one of the important ones.

Wait… what does BTU mean?

BTU stands for “British Thermal Unit” or in other words, a measure of thermal or heat energy. The average furnace produces thousands of BTUs and it’s important to get a suitable unit with the right BTU level for your home.

Bigger is better, right?

No. If the furnace is too large, it will turn on and off more often than you need and reduce efficiency. If it’s too small, it won’t heat your home properly.

How do I calculate BTUs for my furnace?

The rule of thumb for calculating the right BTUs for your home is to take the overall square footage of your living space and multiply it by a factor of BTUs/square foot (don’t worry, there’s an example of how to do this further down this article).

Find the total living area in your house. If you don’t know it, simply measure the dimensions of each room and then add up all the rooms together. For instance, your kitchen might be 12 x 12 feet (12×12 = 144 square feet) and your living room might be 14 x 16 feet (14×16 = 224 square feet). Keep adding up all the rooms until you get a total calculation of square footage.

Using the right BTUs/square foot calculation will depend on what climate you live in. Ottawa-area homeowners can use a measure of 50-60 BTUs/square foot. Use the higher of those two numbers if your home isn’t well insulated or if you’re not sure.


Step 1:

The first thing you want to do is to determine the BTUs required for your home.

1,900 square feet in my house
x 50-60 heating factor
95,000-114,000 BTUs required to heat my home

Step 2:
The second step is to check the new furnace you’re considering for its level of BTUs and then multiply it by the furnace’s efficiency rating. Want to know more about efficiency? See this useful guide.

The new furnace says it has a measure of 120,000 BTU input
x 93% efficiency
111,600 BTU actual output

Compare those two bold numbers. In our example above, the new furnace is well within the range of what we need to heat our home comfortably. If your calculation of the new furnace’s BTUs doesn’t line up within the range needed for your home, keep shopping.

One more thing about BTUs

Just remember that BTUs aren’t the only important factor when purchasing a new furnace. There are only a few things to think about but each of them is important. For a quick overview, see this 5-step guide to buying a new furnace.