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furnace size

When it comes time to replace your furnace, the biggest question is: “what size of furnace do I need?” Furnaces come in various sizes, and the one that’s best for your home depends on a few factors. This blog post will help you determine what size furnace is best for your needs. We will also discuss some common furnace problems and how to troubleshoot them.

How to Measure Furnaces

It’s critical to grasp the fundamentals of furnace ratings before addressing furnace size recommendations.

British Thermal Units (BTUs) are used to measure the heating power of furnaces. One BTU is the heat required to raise the temperature of one pound of water by one degree Fahrenheit. Furnaces are typically rated with an input BTU and an output BTU. The input BTU is the maximum amount of heat the furnace can generate, while the output BTU is the actual amount of heat the furnace produces.

For example, a furnace with an Input BTU of 100,000 and an output BTU of 80,000 has an efficiency rating of 80%. The higher the efficiency rating, the less fuel the furnace will consume to produce heat.

Factors That Affect Furnace Sizes

You need to consider several factors when selecting the size of your furnace.

Size of your home

Larger homes, as you would think, will need larger furnaces than smaller homes. You’ll need to determine the estimated square footage of all heated spaces in your house to calculate an acceptable furnace size.

There’s a high chance you already realize your house’s size, but if not, check out your online property listing or plans. If you can’t discover either of them, you may make an educated guess by multiplying the length and width of every warmed room in the home and summing them all together.

Furnace efficiency

As we briefly discussed before, furnace efficiency is an essential factor when selecting a size. A higher efficiency rating means the furnace will use less fuel to generate heat.

The federal government requires that new furnaces be graded on their annual fuel usage efficiency, which is represented as a percentage. Furnaces with higher AFUE ratings transport more heat into your house, reducing energy waste and pollution.


The average winter temperature in your region will also play a role in what size furnace you need. Warmer climates don’t require as much heat, so a smaller furnace would suffice. Conversely, if you live in an area with very cold winters, you’ll need a larger furnace to keep your home comfortable.

Other factors

There are a few other factors to consider when selecting a furnace size, including:

– The type of insulation in your home

– The number and size of windows in your home

– The ceiling height of your home

– The layout of your home

Once you’ve considered all of these factors, you should know what size furnace you need for your home. If you’re still not sure, you can always consult with a professional HVAC contractor. They will be able to help you select the best furnace for your needs and install it properly.

What is The Right Furnace Size for Your Home

You may be asking how many BTUs you’ll need to heat a home if you’re constructing one. The square footage of your house is the first thing you should consider. In general, larger dwellings need more BTUs to heat. However, keep in mind that this is simply a beginning point.

The furnace BTUs needed for households of various sizes are listed below.

  • 1,200 sq. ft home: 36,000 to 72,000 Furnace BTUs
  • 1,500 sq. ft home: 45,000 to 90,000 Furnace BTUs
  • 1,800 sq. ft home: 54,000 to 108,000 Furnace BTUs
  • 2,100 sq. ft home: 63,000 to 126,000 Furnace BTUs
  • 2,400 sq. ft home: 72,000 to 144,000 Furnace BTUs


When asking, “what size of furnace do I need?” you must consider both the square footage of your home and the climate. Larger homes in colder climates will need larger furnaces than smaller homes in warmer climates. Newer furnaces are also more efficient, so you may be able to downsize your furnace if it’s been a while since you’ve replaced it.

Ultimately, if you’re still unsure what size furnace you need, consult with a professional HVAC contractor. They will be able to help you select the best furnace for your needs and install it properly.

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