What Size Furnace is Right for Your House?

Different homes requires different sizes of furnaces depending on their square footage, age, and insulation. Here’s what you need to know.
Written by Patrick Price
Reviewed by Melanie Reiff
The size of the furnace needed in your home depends on the total square footage of your house. Typically a house will need between 30 and 60 BTUs of heating power per square foot, but this will vary depending on the age of your house and the quality of your insulation. 
Since furnaces often last for years, a lot of homeowners have never had to replace theirs and finding the right one can feel overwhelming. 
It’s important to note, furnaces are not all the same. The one you pick will have a huge impact on your heating bill, how effectively your home is heated, and how long the furnace ends up lasting. In short—choosing the wrong furnace size could be a costly mistake.
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How big of a furnace do I need?

Unfortunately, furnaces do not list what size home they can heat. Instead, a furnace’s power is measured in how many British Thermal Units it produces per hour or its BTUH. 
A BTU is a measure of how much energy it takes to increase the temperature of one pound of water by one degree. Furnaces typically come in either 80,000 BTUH, 100,000 BTUH, or 120,000 BUTH. Larger sizes can be found, but the total BTUH will always be in increments of 20,000. 
How much BTUH your home needs will depend on several factors. Generally speaking, homes have a heating factor between 30 and 60 BTUH, meaning they need somewhere between 30 and 60 BTUs per square foot. The heating factors of your home will vary greatly depending on its size, location, insulation, and age. 


The main factor to consider when determining what size furnace you will need is the square footage of your home. You should be able to find this number on the deed to your home, your closing documents, or the house’s blueprints.
If you don’t have access to any of those documents, you can just measure the square footage of each room you want to heat and then add them up. To calculate a room’s square footage, measure its length and width and then multiply. 
Once your know your home’s square footage, you just need to multiply that number by your heating factor (which is determined by your house’s location) to find what size furnace you need. If you have a 2,000 square foot house and a heating factor of 40 BTU per square foot, for example, you’ll need a furnace with an 80,000 BTUH capacity.


The part of the United States you live in will have a huge impact on your heating needs. Homes in colder regions will require much more power to adequate heat. For simplicity, different regions of the U.S. have been separated into 5 zones depending on their recommended heating factor. Take a look to see what zone your home is in:
  • Zone 1 includes the hottest areas, which require the least heat—such as southern Texas and Louisiana. Homes in Zone 1 only need about 30-35 BTU per square foot.
  • Zone 2 includes areas that are a bit cooler but still very hot, such as Georgia and southern California. Homes in Zone 2 should have 35-40 BTU per square foot
  • Zone 3 starts to include more central areas like Kansas and Virginia. These houses should have 40-45 BTU per square foot.
  • Zone 4 covers areas where the winter can be severe with dangerously low temperatures, such as northern Illinois and New England. If you live in Zone 4, your house will need about 45-50 BTU per square foot.
  • Zone 5 is defined by the truly frigid parts of the country, such as northern Indiana, Wisconsin, and
    . Homes in Zone 5 will need at least 50-60 BTU per square foot.
If you’re not sure what zone you are in, a quick web search of your town’s climate zone should tell you. 
As mentioned above, once you know you recommended heating factor, multiply it by your home’s square footage to find what capacity furnace you’ll need. 


If your home is poorly insulated, you’ll need to take that into consideration when deciding what BUTH you’ll need. 
If you notice any of the following, your house is likely poorly insulated:
  • Inconsistent internal temperature
  • Walls that are cold to the touch
  • Roof leaks
  • Frequent or resilient pest infestations
  • Drafts
  • Frozen pipes
A poorly insulated house in Zone 4 might need 55 or 60 BTU per square foot. In Zone 5, you might need as much as 80 BTU per square foot.


Old houses tend to struggle to retain heat. If your house is more than a few years old, look closely for signs that you are losing heat. Are your windows drafty or cold around the edges? Do you notice any of the signs of poor insulation? If you do, there’s a decent chance your heating efficiency is being affected by your home’s age. 
If your home was originally built with radiators and later had central heat installed, you are likely losing a good amount of heat. Adjust your heating factor accordingly. 
Key Takeaway What size furnace you need will depend mostly on the size of your home and the weather in your area. The age and insulation level of your home will also play a role. Most homes need between 80,000 BTUH and 120,000 BTUH furnaces. 

Are furnaces covered by home insurance?

Whether or not your homeowners’ insurance will cover the cost of a new furnace depends on the reason why it needs to be replaced. If your furnace was damaged by a covered peril then your insurance should cover it. If the furnace is just old and needs replacing due to normal wear and tear, insurance will not cover it. 

How you can save money on your homeowners’ insurance

Replacing a furnace can be expensive, especially if your insurance didn’t cover it. You might be looking to shop for more extensive coverage or just find a better rate on overage similar to what you have now.
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The size of the furnace you need depends on the size, location, age, and insulation of your home. Most homes will need between 30 and 60 BTU of heating power per square foot. Older homes or homes in especially cold areas may require more.
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