What Size Air Conditioner Do I Need? A Boise Tech Answers

August 08, 2018

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Stuck on choosing the right size AC for your home?

Well, we have some good news: You don’t have to worry about choosing size for your air conditioner.

You see, that’s the job of a professional.

In fact, the only way to get an accurate size recommendation for your new AC is to have a professional perform a “cooling load calculation.”

We’ll go into more detail about that later in this article. Below is an outline of what we’ll cover:

  • How AC size is measured
  • Why you need the correct size AC
  • Cooling load calculation: Why you need a pro to help you choose AC size

Let’s start by looking at how AC size is measured in the first place...


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How AC size is measured

When we talk about air conditioner size, we’re not talking about the physical dimensions of an AC system, but rather how much heat it can remove from your home.

BTUs (British Thermal Units) measure the amount of heat an air conditioner can remove from your home in 1 hour. AC systems for most homes range from 18,000 to 60,000 BTUs.

But since BTUs are expressed in the tens of thousands (which can make them confusing to talk about), a simpler way of expressing AC size is through tonnage.

Most residential AC systems range from 1 to 5 tons.

Below is a list of how tonnage equates with BTUs:

  • 1 ton = 12,000 BTUs
  • 1.5 tons = 18,000 BTUs
  • 2 tons = 24,000 BTUs
  • 2.5 tons = 30,000 BTUs
  • 3 tons = 36,000 BTUs
  • 3.5 tons = 42,000 BTUs
  • 4 tons = 48,000 BTUs
  • 4.5 tons = 54,000 BTUs
  • 5 tons = 60,000 BTUs

Now that you know how AC size is measured, let’s discuss why having the correct size AC is important...

Why you need the correct size AC

If you get an incorrectly sized air conditioner (i.e., an AC that’s either too big or too small), you’ll run into issues like:

  • More expensive energy bills: ACs that are too small will run constantly trying to keep  your home cool. On the other hand, ACs that are too big will cool your home too quickly, which means lots of starts and stops. The more your AC turns on and off, the more energy it uses, which means higher energy bills. 
  • More hot/cold spots in your home: If your AC is too big, the AC blower fan won’t run long enough to circulate air throughout your home, which will leave you with hot and cold spots.
  • Shorter lifespan: If your AC has to run longer than it should to cool your home (because your unit is too small), then that means more wear and tear on your AC system. Additionally, if your AC is starting and stopping frequently (because your unit is too big), then your AC will wear out faster, shortening its lifespan and requiring more repairs.

Cooling load calculation: Why you need a pro to help you choose AC size

A cooling load calculation takes into account several factors specific to your home’s construction and existing ductwork, which can help a professional accurately recommend an AC size.

Some of the factors that go into a cooling load calculation include:

  • The size of your home (square footage)
  • Boise climate
  • The quality of your home’s ductwork (are there significant leaks or holes)
  • Your home’s insulation levels
  • Number of doors and windows
  • Number of rooms
  • Construction of your home’s roof
  • And much more

Since a cooling load calculation takes into account so many factors, it can get complicated. Luckily, an AC pro has the necessary knowledge and tools to accurately perform this calculation, so you don’t have to worry about trying to crunch the numbers yourse

Beware of AC pros who only consider the size of your home

Unfortunately, some pros use “rule-of-thumb” estimates to provide size recommendations for your AC.

Most often, these estimates involve statements like “If you have a 2,000-square-foot home, you need an AC with 34,000 BTUs.”

However, like we explained above, your home’s square footage is only ONE factor to consider; not the ONLY factor. So if you hear a tech give you a recommendation like that, consult a different AC contractor.

Want an accurate AC size recommendation for your Boise home?

We’ll send one of our trained techs to perform a cooling load calculation. We can also give you a FREE, honest quote to install your new AC system.

Visit our AC installation page for more information about what to expect when you hire us to install your new AC system.


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