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7 Key Considerations When Sizing a Furnace for a House

Published October 20, 2023
7 Key Considerations When Sizing a Furnace for a House

Do you need help choosing a furnace for your home? Call the experts at Top Flight Heating & Air at 302-329-8003.

Milton’s furnace installation experts know that sizing a furnace for a house takes careful consideration. Properly sizing a furnace for a house ensures your and your family’s comfort no matter how cold it gets outside. A furnace that is too small can lead to cold indoor temperatures, while one that is too large can quickly send the heating bill skyrocketing.

Our HVAC experts explain seven tips to help you choose a furnace that is the right size for your home

 The House’s Square Footage

One of the first considerations to make when sizing a furnace for a house is the square footage. Larger homes need furnaces with a higher heating output. British Thermal Units (BTUs) are the standard method of measuring heat energy and the general standard when heating a home is 30 to 60 BTUs for each square foot of space in the house, but this varies depending on the climate where you live.

To choose a furnace with the necessary power to heat your home, first determine the total number of square feet in your home, then consider the amount of BTUs needed for that size home.

These are some of the furnace BTUs that are standard based on the home’s size:

  • 35,000 – 75,000 BTUs for a 1,200-square-foot house
  • 55,000 – 110,000 BTUs for a 1,800-square-foot house
  • 65,000 – 125,000 BTUs for a 2,100-square-foot house
  • 70,000 – 145,000 BTUs for a 2,400-square-foot house

Although considering the square footage when selecting a furnace is an important measure, it’s not the only heating factor to keep in mind. You will also want to consider the level of furnace efficiency as well as the climate in your area to find out how many BTUs your furnace needs to adequately heat the home.

The Climate in Your Region

The climate in the area that you live in will affect how many BTUs per square foot your furnace needs. Colder climate zones call for a furnace with more heating power, while more temperate climates call for less heating efficiency. The first step is to determine your climate zone. Then, you can see how many BTUs HVAC experts recommend based on your climate zone.

This list will help you choose the correct BTU output per square foot for the furnace you need:

  • Zone 1: Desert and Southern areas: Areas like Texas, Florida, and subtropical areas require 30 to 35 BTUs.
  • Zone 2: Mediterranean areas, including California and Sunbelt areas, require 30 to 35 BTUs.
  • Zone 3: Humid Continental and Oceanic areas, including Virginia and Missouri, require 40 to 45 BTUs.
  • Zone 4: Midwest and Northern New Mexico areas, including New York, Boston, and Chicago, require 45 to 50 BTUs.
  • Zone 5: Northernmost states, including Minnesota’s Twin Cities, call for 50 to 60 BTUs.

To figure out the right level of output, you can multiply your home’s square footage by the BTUs required for your climate zone.

The Furnace’s Heating Capacity

Considering the heating capacity of the furnace is key when determining which size furnace you need. The heating capacity refers to how much heat the furnace puts out per hour in BTUs.

The higher the BTU output, the warmer the furnace will be able to heat the home. The lower the rating, the lower the furnace’s heating capacity.

The Furnace’s Efficiency

Knowing the efficiency rating of the furnace you are considering is one of the critical factors when sizing a furnace for a house. The efficiency rating percentage describes how well the furnace can create a heated air output. Furnaces generally come with at least an 80% efficiency rating. However, the more powerful models have a furnace efficiency rating of 90% to 95%.

Your Home’s Insulation

The level of insulation in your home directly impacts the furnace’s ability to heat your space. If the home has insufficient insulation in the walls or attic, this results in inefficient heating and wasted money. You’ll have to run your furnace for longer, only to lose heat through the attic and walls.

Before purchasing a furnace, it’s helpful to have a professional check your home’s insulation to see if you need more insulation.

Windows in the Home

Checking the size, type, and number of windows in the home before furnace installation is important when sizing a furnace for a house. Double-pane windows efficiently keep the heated air in the home for a longer time. However, smaller windows tend to be more energy efficient than larger ones.

The number of windows in the home can also affect the furnace’s efficiency. A home with many windows will require a furnace with more BTUs, while homes with fewer windows can handle furnaces with fewer BTUs.

Multi-level homes

Homes that have several floors will have varying heating needs than one-level homes. When selecting a furnace, it’s helpful to consider how many floors the home has and the square footage on each floor.

Consult with an HVAC Expert

Taking each heating factor into account will go a long way toward helping you choose the best furnace to fit your home. Before purchasing your new furnace, you will want to consult with an HVAC expert from Top Flight Heating & Air.

Before your furnace installation, one of our heating professionals will provide a consultation to determine which furnace is the right fit for your home. In addition to these seven factors, we also consider ceiling height, age, and the home’s construction.

The level of weatherization that a home has undergone will also affect the ability of the furnace to heat the space. Once we have considered all of the variables, we can recommend the furnace that will heat your home sufficiently.

Top Flight Heating & Air is here for all of your HVAC needs! Call our HVAC experts at 302-329-8003! for help sizing a furnace for a house and for quality furnace installation.

About The Author

Ryan Brower

Ryan Bower is the owner of Top Flight HVAC in Milton, Deleware. He is an expert HVAC techician and writes about his life on the job and HVAC projects that he has encountered throughout his career.
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