When it’s time to replace your furnace, choosing the right size is crucial. A furnace that’s too small won’t be able to properly heat your home, while one that’s too large will waste energy and money. Let’s break down everything you need to know about finding the perfect furnace size for your home.
How Big of a Furnace Do I Need?
The size of furnace you need will depend on several key factors:
- Your home’s square footage
- Ceiling height
- Number and type of windows
- Quality of insulation
- Local climate
- Home layout and design
For example, a well-insulated 2,000-square-foot home could very well need a different size furnace than a similarly-sized home with poor insulation and older windows. Your home’s unique characteristics play a big role in determining the right furnace size.
Understanding BTUs
BTU stands for British Thermal Unit—the standard measurement for furnace heating power. Think of BTUs as your furnace’s heating muscle. One BTU is the amount of energy needed to raise one pound of water by one degree Fahrenheit.
When shopping for furnaces, you’ll see numbers like “80,000 BTU” or “100,000 BTU.” The higher the number, the more heating power the furnace has. But remember – bigger isn’t always better when it comes to furnaces. A furnace that’s too big can lead to short cycling and uneven heating.
How Many BTUs Do I Need For My Furnace?
A good rule of thumb for home heating is that you need 25 to 35 BTUs per square foot in moderate climates, like those typical throughout much of Central and Northern California. However, 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 BTU calculation below.
25 BTU per square foot x 1,600 square feet = 40,000 BTU
Furnace Sizing Calculator
While online furnace sizing calculators can give you a rough idea, they don’t tell the whole story. These calculators work off the general climate and your home’s square footage, but they fail to consider your home’s exact measurements, insulation quality, air leaks, number of windows, and your family’s unique comfort preferences.
To get the most accurate furnace size calculation, you need a professional load calculation, also known as a Manual J calculation.
At Gilmore Heating, Air & Plumbing, our experts perform complimentary load calculations that consider:
- Room measurements
- Insulation values
- Air leak points
- Local climate data
- Your family’s comfort preferences
- Orientation of your home
- Layout of your home
- Windows and doors
- Insulation
- 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.
A professional furnace sizing ensures you get the perfect size furnace – not too big, not too small.
Talk to a Furnace Expert
Buying a new furnace is a big investment, so it’s important to be sure that you have the right size unit for your home.
Take the guesswork out of shopping for a new furnace—contact Gilmore’s expert team for a complimentary furnace sizing. We’ll help you choose a furnace that keeps your home comfortable while maximizing energy efficiency. Plus, we offer convenient financing options to make investing in furnace installation even easier.
