If you are a homeowner, one of the most important things you will ever do is ensure that your furnace is the correct size for your home. Having the right size furnace ensures that your home will always be efficiently heated. Moreover, your family will be much more comfortable, and your energy bills will be more predictable.

It’s further important to consider that a home that does not have an adequately sized furnace is more prone to pipes that can freeze or burst. This means that a furnace that is too small can affect your financial well-being in a number of ways.

However, if you have ever shopped for a furnace, you may have been bewildered by the incredible variety of sizes and models that are available. How do you know which one is right for your home?

The good news is that calculating the correct furnace size for your home is easier than you might imagine.

The two biggest factors that go into determining the correct furnace size for your home are the local climate and your home’s square footage. Other factors do come into play. These may include:

  • The construction of your home
  • Your home’s condition
  • How much sun exposure your home receives
  • The furnace’s efficiency ratings

Let’s take a look at everything you need to know about comparing furnaces, how they are rated and which size is appropriate for your home.

How Do You Measure a Furnace?

How are furnaces rated? The more you know about this system and how it works, the better able you will be to make a well-informed decision.

Any furnace’s capacity is measured in terms of British Thermal Units, which you may see expressed as BTUs. The BTUs tell you how much heat is needed to increase the temperature of one pound of water by a single degree Fahrenheit. You may see BTUs also being used in conjunction with air conditioners and heat pumps.

Although residential furnaces are available in an array of sizes, most homes likely will be well served by a furnace that is rated between 30,000 and 100,000 BTUs.

Which Factors Go Into Choosing Furnace Size?

Several factors may affect your choice of furnace. Let’s examine how certain factors will impact the size of the furnace that you need.

Your home size is one of the most prominent considerations that goes into choosing an appropriate furnace. The larger your house is the larger the capacity furnace you’ll need. This means that you will have to know your home’s square footage before you begin.

Most homeowners already are familiar with their house’s square footage. If you are not, you may refer back to the home listing that was published when you purchased it. Blueprints can help too, and you might also check with your county assessor’s office. You can even consider measuring each room by length and width. Multiply the length by the width of each room to find out how many square feet it contains. Add all of these together to get an approximation of your total square footage.

The climate also plays a critical role in determining the size of your furnace. For instance, your need for heating will vary greatly depending on whether you live in western Arizona or Delaware.

The U.S. actually features several climate zones, making it easier for you to determine just how much capacity your furnace needs.

The U.S. contains seven climate zones. Zone 7 is the coldest while Zone 1 is the hottest. Places like Maine and northern Wisconsin are in Zone 7 while Florida and southern Texas are included in Zone 1. It is possible that some homes in Zones 1 and 2 may not actually need a furnace. In Zone 3, a furnace is more likely to be needed, though it may be possible to get away with a heat pump without a furnace in some places.

While a home of similar size in Texas might only need between 30 and 40 BTUs per square foot to heat their home, a residence in Delaware is more likely to need a minimum of 40 to 45 BTUs per square foot.

What About Furnace Efficiency?

As you begin browsing through available furnace models, you will discover the AFUE acronym. This stands for Annual Fuel Utilization Efficiency. AFUE is expressed as a percentage, and it is a requirement of the federal government that all furnaces display this rating.

The higher the AFUE rating is on a furnace, the bigger the percentage of heat that it will transfer into your home. This translates to fewer emissions and less energy wastage.

Not so many years ago, most furnaces were rated somewhere between 55- and 70 percent efficiency. Recent technological advances have greatly improved these numbers. You may see furnaces with ratings of up to 98.5%. It is true that furnaces that have sky-high AFUE ratings will cost more, but they also do not need to be as large as models that are less efficient. Moreover, a higher AFUE rating means that you will save money on your energy bills because more fuel will be converted into heat that is used by your home.

To find out how truly efficient a particular furnace is, you can multiply the BTU by the AFUE. Let’s take as an example a 100,000 BTU furnace with an 80-percent AFUE. Multiply 100,000 by 0.8 to reach 80,000 BTUs. Thus, the actual BTUs output by this furnace is 80,000.

It also is worth keeping in mind that the efficiency of any furnace decreases over time and with regular usage. A furnace that is nearing the end of its useful lifespan will not be as efficient as a brand-new model.

Other Factors to Consider

We’ve covered the primary factors that you’ll want to weigh as you shop for a furnace. However, there are other things that can affect your choice. As an example, a home that gets a ton of sun exposure every day may not need as large of a furnace. If your home spends most of the day in shadows, it might be wise to choose a furnace with more capacity.

Newer homes that have sufficient insulation are less likely to need a furnace with a large capacity. A drafty older house with insufficient insulation is definitely another story.

The primary purpose behind insulation is to improve energy efficiency. It does this by helping to maintain the home’s temperature. Effectively, this means that insulation keeps the house warmer in the winter and cooler in the summer.

A home that has adequate insulation will provide homeowners with lower energy bills because the heating and cooling systems are not required to put forth as much effort. However, a home that is poorly insulated has more air leaks, and that means that the heating and cooling systems have to work overtime to meet demand.

Even the number of windows in your home may affect the appropriate capacity of your furnace. If your home is newer, chances are good that its windows are up-to-date and well-insulated. Older homes are more likely to have windows with broken seals or miscellaneous damage that may be allowing air to leak.

Calculating Furnace Size for Yourself

It is possible for any homeowner to perform the calculations that will enable them to choose a furnace of appropriate size.

Let’s use as an example a new-construction home that measures 2,000 square feet. Your new home is in Delaware, which puts you in Zone 3. This means that you need to multiply the square footage of your home by the number of BTUs that are estimated for your zone.

The equation would look like this:

2,000 square feet X 40 to 45 BTUs = 80,000 to 90,000 BTUs

Obviously, the results of these equations will give you a range of furnace capacities from which to choose. You would use your knowledge of sun exposure, the amount of insulation your home has, and how old your home is to determine where in the range you should be.

An older home that sits in the shade and may not have enough insulation will need to be at the higher end of the range while a newer home with lots of sun exposure will be safe at the lower end of the range.

Maintaining Your Furnace

If you want your furnace to last for as long as possible, follow these maintenance tips:

  • Try to have a professional assess your furnace at least once or twice a year
  • Taking care of small issues as they arise will prevent them from becoming larger, more expensive problems
  • Change the filter approximately every three months
  • Make sure that your thermostat is properly calibrated
  • Regularly clean the motor, blower, and filter system

Are You Ready for a New Furnace?

Get in touch with Delaware Heating and Air today to learn more about choosing the right size furnace for your home. We’ll even assess the state of your current furnace, provide routine maintenance and take you through the process of buying a new furnace.