If you haven’t shopped around for a new furnace in a while, the process can be a bit daunting. You need to find the right make and model, the kind of fuel source your unit will use and the overall efficiency of the model.

And if that’s not enough, you need to determine the correct size of furnace for your home. The size of a furnace isn’t related to its overall physical size, but, instead, its heating capacity.

Determining the right size furnace for your home can take time for an untrained homeowner. That’s why Ravinia Plumbing, Sewer, Heating & Electric is here to help. Our NATE-certified technicians can come to your home and calculate the appropriate size of heating equipment you need. Keep reading to learn more about why the size of your furnace matters.

How Is Furnace Size Determined

Furnace capacity is measured in British thermal units, or BTUs, in 20,000 BTU increments. One BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit. A mid-sized home with about 2,000 square feet would need about 60,000 BTU output to heat it properly.

How to Determine the Right Size Furnace for Your Home

When determining the right size furnace needed for your home, an HVAC technician will use a furnace size calculator to determine your home’s heating needs.

Some of the factors that determine furnace sizing include:

The home’s square footage

A home’s square footage plays an integral part in determining the size of your furnace. An HVAC technician will take measurements of all the rooms in your home, and also note how high ceilings are if they’re higher than normal or vaulted.


The climate zone your home is in determines the heating capacity you’ll need from your new gas furnace. Since Chicago is in a cold climate zone, homeowners here need a furnace with a larger heating capacity.

Construction, home insulation and more

An HVAC technician will also take note of several other factors in your home when determining the correct furnace size, including insulation levels, the number of windows and the type of construction materials used to build the house. For example, if your home has low insulation levels, it will need a bigger furnace to provide enough heat to keep your family comfortable and safe during the winter.

The Importance of Choosing the Right Size Furnace

Buying a furnace that is too large or too small can lead to serious issues including a decrease in energy efficiency. For example, a furnace that is too large can put out too much heat in your space, causing the thermostat to shut the HVAC system down prematurely. This can also place undue stress on your heating system, leading to expensive repairs and increased wear and tear. Oversized furnaces can also lead to temperature imbalances across the home, short cycling and high operating costs.

Meanwhile, undersized furnaces must run constantly during cold days to increase the indoor temperature. This can lead to high energy bills, excess wear and tear and a shorter system lifespan. It can also cause comfort issues on severely cold days.

Contact Ravinia Plumbing for Furnace Installation

If you’re considering upgrading to a new, efficient furnace, contact the certified heating and cooling system technicians at Ravinia Plumbing. We’ve proudly provided homeowners in Chicago’s Northwest suburbs and Chicago’s North Shore with quality furnace installation services for 95 years. Contact us today to schedule an appointment.