If you’re shopping around for a new furnace, you’ve probably noticed they come in a lot of different sizes—and are wondering which size you need.
Unfortunately, we can’t tell you which size furnace you need without coming to your home.
Here’s why: Finding the right size furnace requires complex calculations of your home and property (more on that later).
In this article, we’ll go over:
- Why correct furnace size is so important
- How furnace size is measured
- What goes into sizing a furnace for your home
Importance of proper furnace size
If your furnace is too big or too small, you'll run into expensive problems.
An undersized furnace will run constantly (running up your energy bills) without ever properly heating your home. It won’t ever meet your heating needs.
An oversized furnace will heat your home quickly and then shut off. This problem, called “short cycling” might sound good, but actually causes:
- High energy bills. Your furnace uses a lot more energy on startup than it does when it’s running. Since an oversized furnace starts more frequently than normal, you’ll pay higher energy bills than you would with a properly sized furnace.
- Uneven temperatures. Because the furnace only runs for a short period of time, it can’t circulate enough air to heat all the corners of your house, creating hot and cold spots.
- Shortened lifespan. Furnaces are designed to run slow and steady. Frequent starts and stops put excess wear and tear on parts, causing them to wear out sooner than normal and need expensive repairs.
Now that you know why furnace size is important, let’s go into how it’s measured.
How furnace size is measured
Furnaces are sized in BTUs (British Thermal Units), which is a measurement of how much heat a furnace can put into your home in 1 hour. For context, one BTU is equivalent to the amount of heat produced by burning through one match.
Residential furnaces range from 40,000 to 200,000 BTUs. Most homes need a furnace somewhere between 60,000 and 120,000 BTUs.
When looking for a new furnace, you’ll also want to take efficiency into account.
For example, an 80,000-BTU furnace rated at 90% efficiency may only deliver about 72,000 BTUs of heat energy per hour into your home (of course, this number can change based on factors like the condition of your home's ductwork).
But the idea is that the more efficient the furnace, the more BTUs will likely be delivered into your home.
Finding the right furnace size and efficiency for your home can be tricky, which is why we recommend leaving it to a professional.
Load calculation: Sizing a furnace for your home
A good, quality furnace installer will determine furnace size through what’s called a “load calculation.” A load calculation is a complex process that takes into account the:
- Size, layout and orientation of your home
- Materials your house is made of
- Local climate of where you live
- Height of your home’s ceilings
- Insulation levels of your home
- Size, orientation and age of windows in your home
- Number of people in your home
- Orientation, size and type of rooms in your home
- Type of roofing on your house
- Number of windows
- And much more
Want to see how complex this process can get? Check out this online load calculator.
Beware of square footage recommendations
If a furnace tech gives you a general recommendation based on the square footage of your home, find another tech.
Every home is different and will require a different size furnace. General recommendations will lead to an over- or undersized furnace which, as we mentioned earlier, is bad news for your budget. Our techs will conduct a heat loss calculation on your home. Basically, a series of calculations and measurements to ensure we find a furnace that’s correctly sized.
Need a quote for a new furnace? Contact a Vancouver tech.Schedule appointment
One of our techs will calculate what size furnace you need for your home and give you multiple system options, along with pricing for each.
Need more information on our furnace installation service? View our furnace installation page