What Size Furnace Do I Need?

When it comes to the comfort and warmth of your home during the cold winter months, choosing the right size furnace is crucial. Many homeowners often wonder about the right furnace size for their homes and does furnace size matter? In this blog, we will discuss what furnace size means, the factors that determine it, and what can happen if your furnace is too large or too small.

Furnace Size: What Does it Mean?

The size of a furnace refers to its heating capacity, measured in British thermal units (BTUs). A furnace’s size doesn’t necessarily refer to its physical dimensions, but rather its ability to generate heat for your home. The most common furnace sizes for homes typically range from 40,000 to 120,000 British thermal units. Finding the right size for your home is critical to furnace efficiency.

Factors That Determine Furnace Size

To figure out what size furnace you need, a heating load calculation must be performed. A heating load calculation is the process of determining how much heat is required to adequately heat and maintain a comfortable indoor temperature for a specific space. 

Several factors determine the size furnace a home needs to efficiently heat the space, including the size of the home, climate, exterior walls, insulation, and construction materials. Let’s take a closer look at each of these furnace sizing factors.

  • Size of the Home: The home’s square footage is one factor used in determining the size furnace needed. The square foot area of the home is used to help calculate the heating load and the necessary BTU per square foot, which determines furnace sizing.
  • Climate Zone: The climate zone heating factor in the region where the home is located affects the furnace’s size. For example, homes in a cold climate zone require a larger furnace size than those in warmer regions.
  • Insulation: Adequate insulation keeps the heat inside the home and reduces the furnace’s workload and improves the furnace’s efficiency, so a home’s insulation is an important factor in determining what size furnace is needed. A home with good insulation requires a smaller furnace than a poorly insulated one.
  • Construction Materials: The materials used in the construction of the home also affect the size of the furnace needed. Homes with large windows and heavy sun exposure, high ceilings, and open floor plans lose heat faster and need a larger furnace.

Oversized vs. Undersized Furnaces

Choosing the wrong size furnace for installation in your home wastes energy, causes uneven heating, and lacks the heating power you need. A bigger furnace isn’t better, and neither is one that is too small.

Oversized heaters and gas furnaces generate too much heat quickly, causing them to shut down before the home reaches the desired temperature. This short cycling can lead to decreased energy efficiency, increased energy bills, decreased lifespan of the oversized furnace, and decreased comfort. 

An undersized furnace, on the other hand, will work harder to heat the home, won’t effectively meet your heating requirement, and waste energy. When the home’s furnace is too small, it leads to decreased furnace efficiency, high energy bills, uneven heating, and the potential for premature furnace failure.

Getting the Right Size Furnace for Your Home

To determine the correct size furnace for your home, it’s crucial to consult a professional HVAC system contractor when purchasing heating and cooling systems. A professional contractor will perform a heat load calculation, which considers your home’s size, climate zones, insulation, and construction materials, to determine the appropriate new furnace size and how many BTUs are needed for your new home heating system.

It’s essential to avoid using a rule of thumb when calculating furnace size, such as choosing a furnace based on the size of your current furnace, or an online furnace size calculator that only considers the home’s square footage to estimate furnace size.

At Grove Heating & Cooling, our experienced HVAC technicians can help you determine the appropriate furnace size for your home. We take into account the unique characteristics of your home, including how many square feet there are, insulation, and other factors to ensure that you have the most energy efficient furnace for your needs. 

Let Us Find the Right Furnace Size for Your Home

Selecting the right size furnace is critical for your family’s comfort and health during the cold winter months. Oversized or undersized furnaces can cause numerous problems, leading to increased energy bills, decreased comfort, and even safety hazards. By consulting with an HVAC professional and considering your home’s square foot area, climate, insulation, and construction materials, you can ensure stress-free warmth this winter season with a new furnace.


At Grove Heating & Cooling, our team of trained heating and cooling system professionals works to ensure that you have a furnace that fits your needs. We understand that furnace size is a difficult question to answer, but our team works to provide you with the most appropriate furnace size for your home to maximize energy efficiency and comfort. Contact us today to book an appointment for a new furnace installation.

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