You have a lot to think about if you’re looking for a new furnace. What AFUE rating fits your budget? Do you want to invest in a high-efficiency furnace? Is a heat pump right for you?

With so many questions to ask, the last thing you should be worrying about is whether or not your contractor sizes your furnace correctly. Unfortunately, it’s all too common for homeowners to have oversized furnaces because their units were not correctly sized.

Why furnaces are often oversized

There are a couple of reasons why furnaces are often oversized in homes. The main thing that it stems back to is the fact that homes used to require larger furnaces. A few decades ago, homes were not as tightly constructed as they are now. As a result, there was a lot of heat loss due to openings in windows and doors as well as poor insulation.

Homes today are very tightly constructed, and it has become common to weatherstrip and caulk sources of possible air leaks. Because homes can contain heat much better now, they do not require as large of furnaces as they used to.

However, some contractors make the mistake of simply replacing old furnaces with new furnaces of the same size, even if they are too large for the home. As a result, those oversized furnaces waste energy and break down much more often than a correctly sized furnace.

How to size a furnace the right way

So what’s the right way to size a furnace for your home? There are several things a contractor should take into account when sizing a new furnace. They include:

  • The size and shape of your home
  • How well insulated your home is
  • What kind of windows you have and where they’re located
  • How many people live in your home
  • The types of lights you have around your home

Manual J, developed by the Air Conditioning Contractors of America, is the standard method used to calculate the correct size of a furnace using the considerations above. A quality contractor can use a Manual J Calculation to correctly measure heat load and choose the furnace size that’s perfect for your home.

If you have any questions about how to size a furnace, or would like to have a new unit installed in your home, contact Jerry Kelly Heating & Air Conditioning, your St. Louis area heating and cooling company.

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