How Big of a Furnace Do I Need For My Home?



 

Part of the challenge of finding the right furnace for your home is that you need to find the right size furnace. A furnace that is too small will have to run more often, running up your heating bill and placing unnecessary wear on furnace parts. A furnace that is too large will cycle on and off more frequently, and will also prematurely wear out furnace parts.

So, choosing a furnace that is appropriately sized for your home is extremely important.

The most important considerations when sizing a furnace is the size of your home, and the weather in your area.

The heat output of furnaces, especially gas furnaces, is typically measured in BTUs (British thermal units). A good rule of thumb for home heating is that you need 25 to 35 BTUs per square foot in the moderate climates that are typical throughout much of California, while you may need up to 45 BTUs per square foot in colder climates, such as those found north of Lake Tahoe.

So if you live in Sacramento in a home that is 1,600 square feet, you will need (at bare minimum) a heater that provides 40,000 BTUs of heat, based on the calculation below.

25 BTU per square foot x 1,600 square feet = 40,000 BTU

However, there are a number of other factors that affect furnace sizing, such as:

  • Orientation of your home: Does your home receive a lot of daylight in the winter, or is it in shadow?
  • Layout of your home: Does your home have a few large rooms, or many small ones? How high are the ceilings?
  • Windows and doors: How many windows and doors does your home have? Windows tend to allow more heat to escape than walls do, and doors that aren’t properly sealed will allow cool air to leak inside.
  • Insulation: Older homes often have poor insulation, which means that a furnace will have to work harder to compensate for the amount of heat radiating outside.
  • Furnace efficiency: Furnaces aren’t just rated by BTU output, but by their efficiency as well. This efficiency rating—sometimes referred to as AFUE (Annual Fuel Utilization Efficiency)—is given as a percentage, and estimates how much of the heat generated by the furnace will actually be delivered into your home. A new 40,000 BTU furnace with an efficiency rating of 97% will produce roughly 38,800 BTUs of heat per hour, while an older 55,000 BTU furnace with an efficiency of 70% will produce 38,500 BTUs per hour.

As you can see, while it’s possible to make a rough estimate based on only weather and the size of your home, there are many other variables should be considered as well. That’s why it’s advisable to have a professional furnace installer take a look.

If you have questions about what furnace is right for your home, call the furnace experts at Gilmore. We’ll come out to your home, examine it and your existing heating system, and then sit down with you, answer your questions, and explain what the right heating solution is for your home. At Gilmore, our goal isn’t just to keep your home warm, but to give you peace of mind as well. So when in doubt, call Gilmore!