What Size Furnace Do I Need? [by Square Footage]

What Size Furnace Do I Need (Based on Square Footage)?

Wintertime brings with it a host of amazing outdoor activities: snowshoeing, cross-country skiing, and building snowmen, to name a few! After the winter fun is done, though, it feels amazing to head back inside to warm up in a toasty living room. If you find yourself returning to a frigid space rather than a cozy one, you might be thinking, “Is it a problem with my furnace? What size furnace do I need to actually heat my home?”

Finding an efficient furnace for your home isn’t a one-size-fits-all task. The best furnace for you depends on many factors, and finding the right furnace size is vital to maintaining a well-warmed home and an affordable energy bill at the end of the month.

If you’re overwhelmed, don’t worry. Keep reading to learn everything you need to know about furnace size and how to choose the furnace you need.

When to Replace Your Furnace

Most of the time, your furnace will tell you when it needs to be replaced if you know the warning signs to look for. These include:

  • Uneven heating across the rooms in your home, or lower heating output than usual
  • Unusually high energy bills
  • Noticeable rust or cracks on the furnace itself
  • Dust or dirt collecting around the house (and you’ve already changed the air filters)
  • Banging, squealing, or other abnormal sounds coming from your furnace

Even if nothing seems visibly wrong with your existing furnace system, if it’s been over 15 years since it was last replaced, it’s time to get a new furnace.

Factors to Consider

There are several things to think about when it’s time to purchase a new furnace to ensure you choose the appropriate furnace size for your space.

Furnace Efficiency Rating

A furnace’s efficiency rating is measured in one of two ways: its Annual Fuel Efficiency (AFUE), or its Heating Seasonal Performance Factor (HSPF).

AFUE is measured as a percentage based on the furnace’s fuel consumption compared to how much heat it produces for your home. If a furnace’s AFUE rating is 85%, that means that 85% of the heat it creates goes directly toward heating your home. Most furnaces today have a rating of 80% or more, and a rating of 90% or higher would indicate a high-efficiency unit.

HSPF is calculated by comparing the furnace’s heat production to its energy consumption. This measurement is expressed in a round number. The higher the number, the higher the furnace’s efficiency rating.

This matters because knowing whether you want to install a high-efficiency furnace or a regular one will help you determine the size of unit you should get. Because a high-efficiency unit wastes less energy than a regular unit, you might be able to get away with purchasing a smaller furnace than you would otherwise buy, saving you money on both purchase costs and your monthly energy bills. However, it’s important to note that high-efficiency units are much more expensive than their run-of-the-mill counterparts, and their installation costs tend to be higher as well. So, it might make more sense to opt for a standard unit rather than a high-efficiency one.

Climate Zone

The climate zone you live in plays a huge role in which furnace size will work best for you. There are five climate zones in the United States, with Zone 5 being the coldest and Zone 1 being the hottest. In colder climates, you’ll need a larger furnace with a higher BTU output than you would in warmer climate zones (we’ll explain what BTU means in a moment).

Specifics of Your Home

In addition to considering the style of furnace you’re purchasing and the climate you live in, you also need to take into account the specifics of your home and its energy efficiency to figure out the size of furnace that will work best for you.

Of course, your home’s square footage plays a major role in this. The more square footage your home has, the bigger you’ll need your furnace to be in order to heat it all.

However, there’s more you’ll need to consider beyond the size of your home. For example, how well-insulated is your home? If you experience a high amount of heat loss in the winter, you’ll need to increase the size of the furnace you plan to buy to ensure that it will sustain a comfortable indoor temperature for you in the winter.

Additionally, how many windows does your home have? With more windows comes more opportunities for heat to escape, meaning that you’ll need a more powerful furnace to adequately heat your home. On the other hand, if those windows experience high amounts of sun exposure throughout the day, this may help your home retain heat rather than become a contributing factor for heat loss.

The final thing you should consider is the age of your home. Older homes tend to be less efficient than newer homes, and no matter how good your home’s insulation is, an old home may not retain heat as well as it should. If this sounds like your situation, opt for a larger size furnace to make sure you can keep your home as warm as you need it to be.

Furnace Sizes

Earlier, we mentioned BTUs, which are the unit by which furnace sizes are measured. The acronym stands for British thermal unit, which is a measurement of heat produced by a certain amount of fuel or energy. Furnaces typically range anywhere from 80,000 to 120,000 BTUs, but they can also be found in sizes both smaller and larger than this range.

Furnace Size Calculator

Now that you know all the considerations that go into choosing a new furnace, the question remains: how many BTUs should you look for in your next home furnace?

The answer primarily depends on the square footage of your home and the climate zone you live in. Heating factor ranges are broken down by climate zone and measured per square foot:

Zone # BTUs Per Sq. Ft.
1 30-35
2 35-40
3 40-45
4 45-50
5 50-60

Start with the heating factor appropriate to your climate zone, as measured in BTUs per square foot. Multiply this number by your house size in square feet, and the result is the approximate furnace size you should use. For example, if you live in Zone 5 (in Minnesota or Wisconsin, for example) and have a 2,500-square-foot home, then the calculation would be as follows:

50 BTU x 2,500 sq. ft. = 125,000 BTU rating

Remember, this is just an estimate, and the proper furnace size for your home will depend on the other factors detailed above in addition to square footage and climate. You should always have an HVAC professional help you determine the right size of furnace for your home.

What If You Have an Improperly Sized Furnace?

Now that you know about furnace sizing, you might be wondering what the issue is with getting the wrong furnace size for your home. After all, is there really a problem with installing a furnace that’s “too big” for your home?

Actually, there is. While you’d think that a larger furnace would heat your home more effectively, the opposite is actually true. Oversized heaters will work too powerfully for short periods of time, leading to constant cycling and inconsistent temperatures throughout your home. Because the unit is turning on and off more frequently, it will also waste energy and may wear out in a shorter time than its intended lifespan.

Furnaces that are too small pose similar problems. Since a furnace that’s too small won’t have enough heating power to maintain your desired temperature, it will run constantly, leaving you with high energy bills despite having a chilly home. Your overworked furnace will probably also need repairs more frequently than should be necessary.

What Size Furnace Do I Need?: Answered

Now you have all the information you need to determine the furnace size you need. Never again will you ask yourself the question, “What size furnace do I need?”

Now that you’ve chosen your new furnace, the next step is to get it installed. You might be tempted to try installation on your own, but to ensure that the job is done well and safely, you should hire a licensed HVAC technician to complete the task.

This is where Aquarius Home Services comes in. As your local HVAC professional, we’re available to help with all your furnace needs, including removal, installation, and repair. Contact us today to find out how we can help you with your next furnace project!

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