What Size Furnace Do I Need? A San Antonio Tech Explains


The answer? It totally depends.

Sizing a furnace is a lot like buying shoes: When you buy shoes, you need to find the size that fits your feet, not necessarily the smallest or biggest size available. Similarly, when you buy a furnace, you need to find the size that fits your home.

So how do you find the right furnace size for your home?

To help you find the right size furnace, you’ll need to have an HVAC professional to perform a load calculation, which takes into account sizing factors specific to your home and current HVAC system.

In this article, we’ll explain:

  • Why you need a correctly-sized furnace
  • Why you can’t size your furnace based on square footage alone
  • Why you need a professional to perform a load calculation

Want a professional to give you a size recommendation for your new furnace? We can help!

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Furnaces are sized according to their heating output (measured in BTUs). Simply put, “bigger” furnaces (furnaces with a higher BTU output) deliver more heat.

And while you may think that getting a bigger furnace is better for your home—that’s not necessarily the case.

If you get a furnace that’s too big or too small for your home, you’ll run into some serious issues.

If your furnace is too big, you face issues like:

  • Higher energy bills: Oversized furnaces heat your home quickly and then shut off. This constant cycling on and off isn’t very energy-efficient, which means you’ll have higher energy bills.
  • Hot and cold spots: If your furnace is shutting on and off all the time, the blower won’t have time to push air to all the corners of your home’s air, leaving you with uneven temperatures.
  • More frequent repairs: All the starting and stopping wears out furnace parts, which leads to more frequent (and expensive) repairs.

If your furnace is too small, you face issues like:

  • Discomfort: An undersized furnace will struggle to heat your home’s air to your desired temperature, which means you’ll likely feel uncomfortable.
  • Higher energy bills: Because an undersized furnace has to run longer to heat your home, it will use more energy, which raises your monthly bill.
  • Shorter furnace lifespan: Longer run times put extra stress on your furnace, which could lead to a premature breakdown.

To avoid these problems, it’s best to find a furnace that fits your home.

Some sources will tell you to simply look at the square footage of your home to find the equivalent furnace size, but that can be very problematic.

We’ll explain why below…

If you’ve done any research online about furnace size, you may have come across sources that tell you things like: “If you have a 2,000 square-foot home, you need a furnace that has a BTU output of 50,000.”

Statements like that should be taken with a grain of salt. Your home’s square footage is only one of many factors that need to be considered when sizing your furnace.

Beware of any HVAC contractor that gives you size estimates over the phone based only on the square footage of your home. If they recommend and install your furnace, you’ll likely get a furnace that’s over- or undersized.

Instead, you’ll want to hire a furnace installer who performs a load calculation…

A load calculation takes into account all of the factors necessary to find the right size furnace for your home.

Some of these factors include:

  • The orientation of your home (south-facing, west-facing, etc.)
  • The landscape and layout of your home
  • How many windows and doors your home has
  • The type of roofing on your house
  • The size of your home (square footage)
  • The insulation levels of your home
  • The materials your home is made of
  • And much more

As you can see from that list, a load calculation can get pretty complicated. In fact, without the right software and measuring tools, it’s nearly impossible for the average homeowner to calculate all of these factors accurately.

Luckily, a licensed and experienced HVAC contractor will have the necessary tools and software to perform a load calculation and find the right size furnace for your home.

Call Today!


Our team of trained comfort specialists can recommend the perfect furnace for your home. Learn more about what to expect when you hire us by visiting our furnace installation page.

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