AC tonnage calculator
Estimate cooling capacity from floor area, climate zone and how the house is built. Useful for a sanity check, not a substitute for a load calculation.
Inputs
Result
How this compares with other methods
The same house, sized three ways. The gap between them is the reason load calculations exist.
| Method | Result |
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Why oversizing is the usual mistake
An oversized air conditioner cools the air to the thermostat setting quickly and shuts off. Short cycles cost you three things:
- Humidity. A coil removes moisture only once it has been running long enough to get properly cold. Short runs leave the house cool and clammy.
- Equipment life. Starting is the hardest thing a compressor does, and more cycles mean more starts.
- Money. Larger equipment costs more to buy, and the ducts to feed it cost more too.
What this calculator does
It starts from a BTU per square foot figure for your climate zone, then adjusts for how the house is built, its ceiling height, sun exposure and occupancy. Converting to tons uses the definition: one ton of cooling is 12,000 BTU per hour.
The construction factor is what most square-footage calculators leave out, and it matters more than the climate zone. A house built in the last fifteen years, or one that has been properly air-sealed, often needs around a quarter less cooling than the same floor area built in 1985.
What a Manual J accounts for that this cannot
Window area, glazing type and which way each window faces. Insulation levels in walls, ceiling and floor. Air leakage, measured rather than guessed. Shading from trees and overhangs. Duct location and leakage. Internal gains from appliances and lighting. Those are the inputs that move the answer, and no floor-area method can see them.
A Manual J costs a few hundred dollars from an independent energy rater, and it frequently pays for itself by letting you buy a smaller system.
Questions
What size AC do I need for 2,000 square feet?
A square-footage estimate gives roughly 3 to 3.5 tons in a warm climate for average construction, and about 2.5 tons if the house is newer or well air-sealed. A load calculation on a well-built 2,000 ft² home often comes out nearer 2 tons. Use the estimate to sanity-check a quote, not to order equipment.
How many square feet does a 3 ton AC cool?
Rules of thumb say 1,500 to 1,800 ft². Measured load calculations on newer homes often show 3 tons covering 3,000 ft² or more. The range is wide because construction matters more than floor area.
Is bigger better for an air conditioner?
No. An oversized unit cools quickly, shuts off, and never runs long enough to pull moisture out of the air, which leaves the house cool and damp. It also costs more and wears faster from frequent starts.
What is a ton of cooling?
12,000 BTU per hour. It comes from the cooling once produced by melting a ton of ice over 24 hours.
Should I just match my existing unit's size?
Only if the existing one worked well. Much installed equipment was oversized to begin with, and if the house has had new windows, insulation or air sealing since, the load is lower than it was.
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Total external static pressure from your readings, plus the friction rate for duct sizing.
CFM airflow calculator
Airflow three ways: from system tonnage, from air changes per hour, and the ASHRAE 62.2 ventilation rate.