Determining HVAC unit size: What ton air conditioner do I need for my house?

Summer in Tennessee can be brutal. With an average high of near 90 degrees in July and August and the occasional 100 degree days, most homeowners don’t want their air conditioners working overtime when the high temps hit.

You also don’t want to buy more AC for your home than needed.

One of the downsides of having an oversized unit is that they cool the air too quickly. That means it will cycle on and off too often, which will shorten the life of the unit.

Air conditioners operate most efficiently when they run for a long period. If the unit doesn’t run long enough, it won’t extract enough moisture from the air. As Tennesseans know, the more humid the air, the damper it feels. And if the air is humid and cold, it will feel clammy.


So what size HVAC unit does a building need?

It depends on the building, residential and commercial buildings have different needs.

Knowing the size of your HVAC unit isn’t just the physical dimensions. It’s the BTUs.

A BTU is a British Thermal Unit, which is the traditional measurement used in the United States. A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

For residential buildings, multiply the square footage of the area that needs to be cooled by 25 BTUs to calculate the cooling needs of your home. So for a 1,000-square-foot house needs 25,000 BTUs.


But HVAC units are sold by the ton?

One ton can remove 12,000 BTUs in an hour.  So your 1,000-square-foot house needs a 2-ton unit. (1,000 X 25 = 25,000/12,000 = 2.5 tons)

This simple formula creates a pleasant environment inside, no matter the summer heat outside.

Business owners, on the other hand, have a harder task in front of them to ensure their AC unit is the correct size to help control their overhead costs.

Commercial buildings generally have higher ceilings, more traffic and different insulation from residential units.

The formula is to divide the square footage by 500 then multiply this number by 12,000 BTUs.

Now you need to account for all the sources of heat, like windows, doors and people. Add 380 BTUs per person and 1,000 per sun-face window and door. If there is a kitchen, add another 1,200 BTUs.

This will give you a good estimate of how large a unit you need to meet your needs.

By choosing the appropriate cooling capacity, whether it is for a whole house or even a window unit, you will get the best efficiency and lower your operating costs.

This will give you an idea, but the assistance of a heating and cooling professional will go a long way.  Need help with your heating and cooling needs, call TMC at 615-255-6677