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Furnace Size Calculator

On this page:
  • Use our furnace size calculator to find how many BTUs your furnace needs
  • Is furnace size important for your home?
  • What factors contribute to furnace size?

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If a furnace is too small for a home, it may be overworked. Not only will this shorten the furnace’s lifespan, but homeowners will wind up paying more in utilities due to how often the furnace needs to run to adequately heat the home. Our furnace size calculator can tell you how many BTUs your furnace should be.

Finding the right size furnace depends on where the house is located, how many square feet it is, and the age of the home’s windows and insulation. Here is what to know.

What Size Furnace Does a 2,000 Sq. Ft. Home Need?

Let’s start with the basics. For a 2,000 Sq. ft. home, you will need to install a 60,000 – 80,000 BTU furnace.

Why? The calculation is simple. A basic rule of thumb for furnace size calculation is that it takes 30 BTUs for every 1,000 square feet of house. So, if you have a 1,000 square foot house, you need a furnace that has a 30,000 BTU output. 

However, there are a few other things to take into consideration before you apply this formula to your own home.

The BTU output you need may differ based on which climate zone you live in. If you live in a colder region, you need more BTU per square foot to heat your home compared to homes in warmer regions.

Our furnace size calculator takes these factors into account along with whatever existing windows and home insulation you may have.

Furnace Size Calculator

Ready to find what size furnace you need? Enter your home’s square footage into the calculator to get started. Our heating and cooling map below will show you what climate zone you live in.

USA climate zones map
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USA climate zones map

Enter your home’s square footage to get started:

Please enter a number between 500 and 10,000.

Look at the map above. What zone do you live in?

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Are your windows and/or insulation 15 or more years old?



Heat pump

Your furnace should be


If you don’t know the square footage of your home, multiply the length and width of each room that you wish to heat. Add the measurements for each room together and you will come up with the square footage of your house. Then, use the furnace cost calculator above to find what size furnace you need.

What Is BTU for Furnaces?

BTU stands for British Thermal Unit. It is a measurement that determines the thermal energy output of various devices. To put it more scientifically, BTU measures the energy it takes to warm one pound of water by one degree Fahrenheit.

More simply, it represents your furnace’s capacity for how much energy it will take to warm your home.

For this post, we will apply BTUs to home furnaces, but be aware BTUs can also be used to determine the energy it will take to cool your home.

Why Does Furnace Size Matter?

A smaller furnace size than what you need will give you uneven heating and require more energy to maintain optimal temperatures in your home. This will result in higher energy bills.

A bigger furnace size than what you need will lead to overheating areas of your home and yield more power than necessary for your home size. It will also damage the heat exchanger in the furnace because the unit will more frequently turn on and off again as it reaches the set temperatures in your thermostat. See how a furnace works.

Both of these scenarios will ultimately wear on the furnace and shorten its lifespan.

Factors To Consider When Choosing The Right Size Furnace For Your Home

Your Home’s Age

Typically, older homes are less energy efficient and may require more BTUs to stay warm. This may not apply to you if you have significantly remodeled not only the portion of the home you can see, but also elements you cannot see, like insulation. Keep reading to learn more about the areas of your home that can help reduce what size furnace you need.

Quality of Insulation

Similarly, if your home has poor insulation you may need a larger furnace. Why? Well, insulation plays an important role in keeping the conditioned/heated air in your home from transferring through the walls and outside. Similarly, it helps keep the outside temperatures from transferring into your home.

Quality and Number of Windows

If you have old windows, the window frames may be drafty and allow heat to escape. Newer windows will have better insulation. Windows facing the south will also passively heat your home, as they allow for sunlight to enter the home and retain the warmth.

Your Home’s Location

The energy your furnace requires definitely depends on where you live in the United States. If you live in Minnesota, you’ll want a furnace with a higher BTU output than someone in Louisiana. If you live in a cold climate, you may want to use a BTU of about 80 instead of 30 to calculate your furnace needs in the formula you read about above.

The Furnace’s Energy-Efficiency Rating

Newer furnaces will have a tag that shows their energy efficiency ranking. It’s best to choose a furnace with the highest ranking within your price point. Even if your home is not especially energy efficient, having an efficient furnace will keep your bills as low as possible while you stay warm.

New Furnace Installation Cost

When you have calculated what size furnace you need, click here to see the cost estimate for installing a new furnace in your home.

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Will I Need a Furnace Contractor?

A trusted HVAC contractor will know about the latest energy-efficient furnaces on the market. They can also determine if your furnace needs to be repaired or replaced completely.

Working with an HVAC contractor will also help to guarantee you get the best furnace for you and your family’s needs. In addition to making sure it is properly installed, a contractor will present a few furnace options and explain the pros and cons of each type.

If you’ve never replaced a furnace before, consult with an HVAC contractor before you undertake a furnace replacement project. They can help show you what to do as well as suggest basic maintenance tips for prolonging your furnace’s life.