There are lots of reasons why you want your HVAC equipment installed by a licensed, certified and trained technician. Some of those reasons come into play long before the technical challenge of actually installing a new system; the initial task of sizing a furnace to a home is a technical process that requires special knowledge, and getting the calculations wrong can be costly.

An Ill-Fitting Furnace

You already know that proper sizing of air conditioning systems is essential to comfort and energy efficiency. An air conditioner that is too small will run constantly, which is expensive, and it may never get the home to reach its thermostat setting. One that’s too large will cool down the house too quickly, resulting in cooling cycles that are too frequent and that wear down parts prematurely.

Furnaces face almost the exact same problems when they aren’t sized properly. Undersized systems will run all the time, racking up huge bills while struggling to heat the home. Oversized systems are likely to make some rooms too hot, especially the ones closest to the furnace. They will also cycle on and off too regularly, all but ensuring more frequent repair calls.

Better Data, Better Results

Some HVAC manufacturer websites offer charts or calculators to help you estimate furnace size based on the square footage of your home, and these can be useful for getting a general idea of what size is appropriate. But there are much more accurate calculations that an experienced HVAC technician can perform to ensure the best possible fit, and with so much riding on the performance of your furnace, it’s important to get this step right.

To perform these calculations, a technician will need to take measurements and inspect several elements of the home, including:

  • Square footage
  • Cubic feet of indoor air space
  • Ductwork efficiency
  • Integrity of the home envelope
  • Climate zone
  • Type and amount of insulation
  • Sunlight exposure
  • R-values and U-values of windows, doors and other elements

As you can see, these are more than back-of-the-envelope calculations, but getting an accurate assessment prior to choosing your system is critical to ensuring a long and energy-efficient life for your new furnace.

Measure Twice, Upgrade Once

If your furnace is exhibiting some of the problems described above, it’s possible that it’s improperly sized. The most reliable way to know for sure is to have an HVAC technician examine your furnace and assess your home’s heating needs. And if it turns out that your furnace is a major mismatch for your home, it may be that the most cost-effective way forward is to replace it.

On the other hand, if you’re happy with your furnace’s performance and it’s about to become due for replacement, you shouldn’t necessarily jump right in and buy a replacement of the exact same size. By upgrading to a more efficient model, you may be able to buy a smaller furnace while still getting the same heat output as before.

Furnace heat output is measured in British Thermal Units, or BTUs. But when you check furnace specs, there are two key numbers: the input BTUs, which is the amount of heat the furnace actually generates, and the efficiency rating, which is the percentage of that heat that makes it into your living spaces.

So for example, if a furnace has an input BTU of 100,000 and an efficiency rating of 90, it will deliver 90,000 BTUs of heat into the home (because 90,000 is 90 percent of 100,000). But an older furnace that has an input BTU of 120,000 and an efficiency rating of 75 will put out the same amount of heat -- it’ll just use more energy in the process. So when buying a new furnace, you should focus on the BTUs your home needs -- as calculated by your HVAC technician -- rather than the specs of your old, outdated furnace.

Are you ready to find out what size furnace is a perfect fit for your home? Contact your local One Hour Heating & Air Conditioning today to schedule a consultation.