What Size Furnace Do I Need for My Home? A Portland Tech Explains

Furnace installation in Portland

Retiring your old furnace? One of the most common questions we get from homeowners is how big a furnace needs to be to properly heat a home in Portland.

Unfortunately, we can’t get the answer by asking about your old furnace size. In fact,the only way to answer this question is to have an HVAC consultant swing by and perform a load calculation on your home.

Four Seasons doesn’t mean to make it tougher to find the answer. A load calculation really is the only way to determine furnace size.

Now, what we can do is explain the process of sizing a furnace. That way, you know exactly what questions to ask when the tech arrives to perform a load calculation on your home.

So here’s what we’ll go over in this article:

  • Why proper furnace size matters
  • How furnace size is calculated
  • What goes into a load calculation
  • How to tell if a tech knows his facts about furnace size

If at any point in this article you decide that you just can’t wait to find out what size furnace you need, just give Four Seasons a call! We can have a trained technician perform a load calculation on your home fast, sometimes even the same day you call. You can also view our furnace installation service page, to see how our process goes!

Call us at 503-538-1950 or contact us online to schedule your visit today.

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Why proper furnace size matters

Like the story of Goldilocks and the Three Bears, you’re not gonna want a furnace that’s too big or too small. You’re gonna want a furnace that’s just right for your home.

Furnace size needs to be just right because anything outside of that “Goldilocks zone” is going to cause problems for your home.

Get a furnace that’s too big, and you’re going to encounter:

  • High energy bills
  • A shortened furnace lifespan
  • Cold spots through the home that never warm up

But get a furnace that’s too small and you’ll see:

  • High energy bills
  • A chilly home no matter how long your furnace runs for
  • A shortened furnace lifespan
  • More frequent repairs

How furnace size is calculated

Furnace size is based on what’s known as British Thermal Units, or BTUs. BTUs are a measure of heat output. The higher the BTU output, the more heat the unit can provide.

What’s the average number of BTUs in a standard residential furnace you ask? We’d say it’s around 40,000 to 100,000 BTUs. But the Four Seasons’ team has installed furnaces with BTU outputs as low as 30,000 and as high as 130,000.

What goes into a load calculation

A heat load calculation measures how quickly heat is lost within a home. The calculation takes into account many different factors which pertain to heat loss, some of which include:

  • Number of doors and windows found within the home
  • The square footage of the home
  • The home’s floor plan
  • The amount of trees surrounding the home
  • The orientation of the home
  • Materials used to build the home (such as brick, stone or adobe)
  • Insulation materials found within the walls and ceilings (like spray foam, fiberglass or cellulose)
Furnace size measured in BTUs

Furnace size is measured in British Thermal Units, or BTUs

...and that’s not even a comprehensive list!

The sheer number of variables which go into calculating a home’s heat load is why we always recommend hiring a professional to perform them. Every HVAC pro will tell you the same thing.

And if a contractor claims you don’t need one? Well...you’ll definitely want to read the next section to find out why that contractor shouldn’t be performing any furnace installations, period.

How to tell if a tech knows his facts about furnace size

You can tell a lot about an HVAC contractor based on their criteria for selecting a furnace size.

Below we’ll give you three hypothetical conversations a homeowner could have with an HVAC contractor. If you hear anything out of a contractor’s mouth that sounds similar to the statements below, run!

Hypothetical conversation #1

What the contractor tells you:

“We don’t need to drop by the house. Just tell us what size furnace you already have and we’ll install the same size.”

What he really means:

“We’re lazy and just want to sell you a new furnace fast.”

Our take: An HVAC contractor probably has no idea who installed your original furnace. For all they know, it could be massively over- or under-sized. No matter what, it means you’re getting a bad deal. A good HVAC contractor will never blindly choose a furnace size based on your current furnace size.

Hypothetical conversation #2

What the contractor tells you:

“Sure we can tell you what size furnace you need. Just tell us the square footage of your home.”

What he really means:

“We’re more interested in your money than doing a good job on your furnace installation.”

Our take: Square footage is just one of many factors that an HVAC contractor will look at when performing a proper load calculation. If one goes by square footage alone, it could lead to massive energy bills, a freezing cold home, or both.

Hypothetical conversation #3

What the contractor tells you:

“Load calculation? What’s that?”

What he really means:

“I’ve never installed a furnace in my life.”

Our take: Run for the hills! If any HVAC contractor tries to sell you a furnace without making any suggestions at all about a load calculation, he should be escorted off your property immediately (if he even made it that far.)

Nobody Knows Furnaces and Load Calculations Like Four Seasons

Four Seasons A/C & Heating has Portland’s best prices for professional furnace installations. Schedule today by giving us a call at 503-538-1950, or set up an appointment online.

We look forward to hearing from you!

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