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06 Jan

How to choose the right size furnace for comfort and efficiency

Comfort is key in the winter, and a comfortable home depends on having the right size furnace. Bigger isn’t always better. The perfect size depends on the size of your home, the quality of the insulation and the climate where you live.

Having the right size furnace can help you achieve the perfect comfort level with ideal energy efficiency. It’s not too hot, nor too cold, and you don’t suffer expensive energy bills in the process. Here is how to choose the right size furnace for your home and geographic environment. 


Why the right size is so critical

Ideally, your furnace heats your home efficiently, comfortably and consistently. A furnace that’s too small for your home will redline too often, consuming expensive fuel in the process. Furnaces that are too large are also problems. They heat a home too quickly, which leads to short cycling. Your furnace turns off and on repeatedly, never hitting that sweet spot. This wastes energy and overly strains your furnace, wearing it out prematurely.

Choosing the right size for your furnace

Determining the ideal furnace size depends on the dimensions of your home, insulation quality and geographic location. The style of your home — whether it’s a ranch, split level, or several stories — can also impact how big a furnace you’ll need. The number of windows you have in your home can also be a factor. 

In calculating a general range of surface area needed, a professional HVAC Technician will only include rooms that will be heated in the square footage. Keep in mind this may vary from the actual square footage of your home.


Calculating furnace BTUs for square feet

Furnace capacities are measured in British Thermal Units, or BTUs. This is the amount of energy necessary to increase the temperature of one pound of water by one degree Fahrenheit. Keep in mind this number is just an estimate for calculation purposes. Ultimately, you will want a professional HVAC specialist to determine the proper size furnace for your home.

The number of BTUs per square foot depends on geographic location. There are five standard zones in the United States, all with different BTU requirements. Zone one is in the southern United States where temperatures are the highest. Zone five is generally located in the north of the U.S., where temperatures are the coldest. 

BTUs per square foot in each zone are as follows:

  • Zone 1: 30-35
  • Zone 2: 35-40
  • Zone 3: 40-45
  • Zone 4: 45-50
  • Zone 5: 50-55


Trust the advice of a HVAC specialist

You can make an educated guess on the right size furnace of your home, but it’s still a guess — and a complicated one at that. There are so many factors that can affect the calculation: the number of windows in your home, how many floors you have, even the amount of tree shade in your yard. Determining an exact number can be difficult. Ultimately, this is a calculation that is best left to a trained HVAC Technician. 


Installing a furnace? Contact HVAC 911!

If you need help determining the ideal size furnace to purchase, contact HVAC 911! We are a referral network of trusted heating, ventilation and air conditioning specialists. They can ensure you purchase the right size furnace and schedule installation for the perfect comfort level that is energy efficient.


All of our HVAC Techs are highly trained and fully vetted. They are drug tested, insured and bonded. Call HVAC 911 for a trusted HVAC specialist today!