Air Conditioner Sizing: What is a Heat Load Calculation?

Air Conditioner Sizing: What is a Heat Load Calculation?

tape measure with building plansIn our previous article we talked about the costly consequences of installing an air conditioner that is too small or too large in a Phoenix-area home.

We came to the conclusion that, in order to find a correctly sized air conditioner, you need a professional to perform a heat load calculation (also known as a Manual J load calculation)

Read on to learn:

  • What is a heat load calculation
  • Factors involved with the heat load calculation
  • The dirty secret other contractors don’t want you to know about how they size your air conditioner

What is a heat load calculation?
Let’s back up and explain what a “heat load” is. Essentially, heat load refers to the amount of heat that must be removed from your home over a given period to meet a home’s cooling requirements.

So a heat load calculation calculates what cooling power your air conditioner needs in order to remove all that heat to keep you nice and comfortable.

This cooling power or “cooling capacity” is measured between 1.5 and 5.0 tons.

Now, if you can remember anything from this article, let it be this: The tonnage you need is NOT based solely on the size on your home.

That’s ONE important factor, but there are others as well. That’s what makes the heat load calculation a complex beast

Some factors included in a heat load calculation
The factors below contribute to how much heat your home holds and how much heat it gains:

  • Square footage of the home
  • Materials used in the construction of your home
  • Structure of your home (like if you have vaulted ceilings)
  • The climate zone you live in
  • Number of windows and skylights in your home (and their length and width)
  • Home’s orientation in relation to the sun
  • How well your walls and attic are insulated

Now, you’d think that since this calculation is so important to find a rightly sized air conditioner, that all contractors would do it? Well…

Not everyone does heat load calculations
Many contractors will do a “rule of thumb” calculation based solely on the square footage of your home.

So if you get someone who says you absolutely need an air conditioner of a particular tonnage, but they haven't investigated your home, then they aren’t doing their due diligence.

Do this: Ask potential contractors you’re thinking about hiring to install a new air conditioner about how they determine its size. If they don’t reply that they’ll perform a heat load or Manual J load calculation, then look elsewhere.

Do you need a new air conditioner that’s correctly sized for your Phoenix-area home? Contact us online to get a free estimate.

Got any other questions about heat load calculations? Ask one of our experts. We’re always glad to hear from you!