If you’re always either too hot or too cold at home, you may have had the wrong-sized heating or cooling system installed. But it doesn’t have to be that way.
There are two main rules to knowing how to size a furnace, boiler, or air conditioner:
Keep reading to learn what it takes to properly size your heating and cooling system. If you want a rough idea now, go straight to our HVAC sizing calculator.
An ACCA Manual J Calculation is the only trusted way to get the right-sized heating and cooling equipment for your home.
Any AC or furnace size calculator you find online won’t give you anything more than a guess of your home’s heating and cooling load.
Interestingly, that’s the same thing some contractors do. They use rules of thumb based on your home’s square footage to pick equipment that they think will work. Oftentimes, to cover themselves, they’ll oversize the equipment, which wastes energy and money down the road.
To maximize your comfort, we'll provide you a custom load calculation based on Manual J principles for a small fee. You can call us at
Although we still recommend having your professional installer perform a full Manual J before installation, our professional sizing will give you the closest you can get without spending tons of money.
-->There are four main factors a Manual J Load Calculation considers that many rules of thumb and cheap calculators don’t:
“Rule of Thumb” guesses don’t take all these variables into account. That’s why, when it comes to furnace and AC sizing for you whole house, go with a Manual J Calculation.
If you don’t want a central heating or cooling system and are instead installing a mini split or PTAC unit, the calculation becomes much simpler. Essentially, you are now sizing for either a single-room, or multiple rooms separately. Our calculator below can help with that.
Use that calculator only as a guide, though. For best comfort results, you should still get a Manual J Load Calculation done, even if just for a single-room. Although you’re less likely to get a single-room application “wrong,” it can happen, so why not protect yourself?
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