Often people only look at tons or BTUs when buying an air conditioner, but there are many other factors that are important to choose the right size. The wrong size AC consumes more power, causes cooling problems and can also reduce its lifespan. In this guide, we will learn step-by-step how to choose the right air conditioner for your home in the US.
8 Steps for Calculating Right Size of Air Conditioner for Home
Step 1: Know the size of the room/house (Square Footage)
First of all, it is important to know the total area of the area to be cooled.
- To measure a room: Length × Width = Square Feet.
- If the whole house is to be cooled, add the total of all the rooms.
Example: If the room is 12 feet × 15 feet → 180 square feet.
Step 2: Calculate BTU (British Thermal Units)
The cooling capacity of an AC is measured in BTUs. Below is a general guide:
Area to be (in Sq. Ft.)
100 – 150
150 – 250
250 – 300
300 – 350
350 – 400
400 – 450
450 – 550
550 – 700
700 – 1000
1000 – 1200
1200 – 1400
Capacity (in BTU’s) Required
5,000
6,000
7,000
8,000
9,000
10,000
12,000
14,000
18,000
21,000
23,000
Step 3: Consider Climate Zone
Different regions in the USA have different climates. Cold states (like Minnesota, Wisconsin) and hot states (like Texas, Florida, Arizona) have different cooling needs.
Climate
Very hot (South & Southwest)
Cool areas (North & Northeast)
What to do
Increase BTUs by 10-20%
Keep original BTUs or reduce slightly
Step 4: Number of people in the room
Add about 600 BTUs for each additional person
Example: If 4 people usually live in the room → (More than 2 people = add 2 × 600 = 1200 BTU extra)
Step 5: Sun Exposure
• If the room is directly in the sun (South/West facing) → increase the BTU by 10%
• If the room is shady → reduce the BTU by 10%
Step 6: For the kitchen/cooking area
If the AC is being installed in the kitchen, add at least 4,000 BTU extra, as the heat increases while cooking.
Step 7: Pay attention to windows and insulation
- Older homes with poor insulation require more BTUs.
- If the home has double glazed windows and good insulation, lower BTUs may work.
Step 8: Ducted or Split System?
Whole house HVAC is designed for central air systems. An HVAC expert performs Manual J Load Calculation.
• For mini-split or window ACs, the above steps are sufficient.
Finally: Consult an HVAC Professional
If you are installing a whole house cooling system, getting a Manual J Load Calculation done by a professional is the best way to go. This will not only ensure proper cooling but will also save energy.