What size furnace do I need for my home.

How Do I Know What Size Furnace to Buy for My Home?

January 27, 2020

When it comes time to replace your furnace, you’ll have many options to choose from. Whether your priority is maximizing efficiency or finding the most affordable furnace option, you’ll need to figure out what size furnace is the right fit for you. We’ll discuss why furnace size matters, along with a number of different factors that can help you figure out how to determine furnace size for your home.

How to Determine Furnace Size for Your Home

Maybe you’ve wondered — “How do I know what size furnace to buy?” Maybe you’ve never thought about furnace size at all.

Many people don’t realize that furnace size is an important factor when choosing a new furnace for your home. If you install a furnace that’s too small, it may not adequately heat your home. However, dealing with an oversized furnace can cause issues as well. Choosing the right size furnace for your home will improve comfort and maximize efficiency.

HVAC professionals use data and mathematical formulas to figure out what size furnace is necessary to properly heat a space. One industry standard is the Manual J Load Calculation, developed by the Air Conditioning Contractors of America (ACCA).

How to Determine Furnace Size Using a Manual J Load Calculation

Performing HVAC load calculations can be time consuming and complex, so many HVAC contractors use rules of thumb and estimates to determine what furnace size is best for any given space. But when customers come to Lozier asking, “What size furnace do I need?”, our HVAC experts use a Manual J Load Calculation to determine the right furnace size according to the heating and cooling needs of their home or business.

Using a Manual J load calculation provides the most accurate information about how much energy is needed to heat or cool a space. This load calculation formula considers some of the following factors:

  • Square Footage of the Space
  • Insulation Type and Quality
  • Indoor and Outdoor Temperatures
  • Humidity
  • Number Doors and Door Placement
  • Number of Windows and Window Placement
  • Number of Occupants
  • Orientation of the Lot

What Size Furnace Do I Need?

Where you live also impacts what size furnace you need to heat your home. The climate in Minnesota is much different from the climate in Arizona. Generally, people living in colder geographic areas need a furnace that outputs more BTUs per square foot. Local HVAC professionals will be able to recommend the best options for your area.

Why Does Furnace Size Matter? Here’s What Happens When a Furnace is Too Small

When a homeowner is looking for an affordable furnace option, they may end up buying a furnace that is too small for their house. Going for the cheapest or the smallest furnace is not always a good idea. In fact, attempting to save money by buying a small furnace may end up costing more money in the long run. When you’re asking an HVAC professional, “How do I know what size furnace to buy?”, they should warn you of the consequences of installing a furnace that is too small.

Small Furnace Problem #1: Overworking Your Small Furnace

If a furnace is too small for a house, it may need to run constantly in order to maintain a comfortable temperature for occupants. When a furnace is overworked, it may require more maintenance, and it may have an overall shorter lifespan. We recommend investing in a furnace that can handle the heating needs of your space.

Small Furnace Problem #2: When Saving Money Costs You Money

Saving some cash upfront by buying a smaller or cheaper furnace can end up costing you more over the years. An overworked furnace will break more often, and maintenance costs add up. You may even end up needing another new furnace sooner. Constantly running a furnace that can’t keep up with your needs will also result in higher energy bills. It’s a good idea to pay a little bit more upfront for a furnace that can adequately heat your space without running 24/7.

Small Furnace Problem #3: Small Furnace, Cold House

What happens when your furnace is too small? Your house will be cold. This is perhaps the most obvious reason not to buy a furnace that is too small for your house. A small furnace will result in insufficient heating, leaving some rooms colder than your preferred temperature.

Dealing With an Oversized Furnace

When it comes to furnaces, bigger isn’t always better. In an effort to find a furnace that can handle their heating needs, some people will overshoot and purchase a furnace that is far too big for their space. It doesn’t help that some HVAC salespeople will try to upsell customers and convince them to buy the biggest, most expensive furnace available.

Dealing with an oversized furnace can be just as troublesome as dealing with a small furnace, but the issues are slightly different.

Oversized Furnace Problem #1: Uneven Heating

When a furnace is too large for its space, it will often run in short bursts (see problem #2). This often results in uneven heating throughout a house — some rooms may be freezing while others feel like an oven.

Oversized Furnace Problem #2: Short Cycling

When a large furnace is installed in a small space, it heat the whole space quickly. This typically leads to an issue called short cycling.

What is Furnace Short Cycling With an Oversized Furnace?

Furnace short cycling occurs when a furnace kicks on for a short period of time and then turns off. When a furnace is too large for its space, this stop-and-start cycle happens continuously, leading to high energy bills and increased wear and tear on your furnace. Short cycling can cause damage and reduce the overall lifespan of your furnace.

What Size Furnace Do I Need For My Home?: The Bottom Line

Installing a furnace that is too small results in a number of problems and expenses. Purchasing an oversized furnace produces similar issues. Ultimately, if you get wrong-sized furnace, you can expect to deal with increased costs, more maintenance needs and a home that isn’t heated comfortably.

When your system is the right size for your house, you and your family will be more comfortable and your furnace will be more efficient. This means lower energy bills, fewer maintenance needs and a longer life for your furnace.

Let Lozier Help You Determine Furnace Size For Your Home

When you’re furnace shopping and wondering what size furnace you need, talk to Lozier. Our local Des Moines HVAC experts have years of experience advising customers on choosing the right furnace for their needs. If you need a new furnace or if you have questions about your HVAC system, reach out to us today!