BTUFit › Central AC size › 1,500 sq ft
What size AC unit for a 1,500 sq ft house?
Quick answer: 2.5 tons in a mixed climate with average insulation, but the honest range runs from 2 tons in cool zones to 3 tons in the hot, humid South. Find your cell:
| Insulation | Hot-humid | Hot-dry | Mixed | Cool | Cold |
|---|---|---|---|---|---|
| Older / drafty | 3.5 tons | 3 tons | 3 tons | 2.5 tons | 2 tons |
| Average | 3 tons | 3 tons | 2.5 tons | 2 tons | 2 tons |
| Tight / newer | 2.5 tons | 2.5 tons | 2.5 tons | 2 tons | 1.5 tons |
2.5 tons in a mixed climate, and the argument on a 1,500 sq ft house is almost always whether it should be 3. There is no 2.75. The step from 2.5 to 3 is a 20% jump in capacity, and at this footprint it is the difference between run times long enough to wring water out of the air and eight-minute cycles that leave the house cold and clammy. Drafty single-pane houses do earn the 3 tons, and the table above shows exactly that. A 1990s or newer 1,500 sq ft house with decent windows does not.
Before arguing about the half ton, look at the ducts, because on houses this size they are usually what is actually limiting capacity. 2.5 tons wants roughly 1,000 CFM at the conventional 400 CFM per ton. Plenty of 1,500 sq ft ranches were ducted for a furnace and a smaller condenser, with one central return grille that chokes anything bigger. The field number to ask for is total external static pressure. Equipment is designed around 0.5 inches of water column, and measured values of 0.8 to 1.0 are routine in real houses. A system fighting that never delivers its nameplate tonnage, which is how people end up with an oversized unit that still cannot keep up.
One more thing specific to this footprint: if it is a slab ranch with the trunk line in a vented attic, duct leakage is conditioned air you are selling to the attic. Seal and insulate that before buying a larger unit to overcome it. Ask for the AHRI matched-system number too, because a 2.5-ton condenser paired with whatever coil was already in the closet does not deliver the SEER2 on the sticker.
Replacement cost ballpark for a 1,500 sq ft house (US, 2026): systems around 2.5 tons in a mixed climate commonly price in the $4,500–$9,000 installed range for a straightforward swap. New ducts or panel work push past that. These are national public-guide ranges, not a bid.
Adjust the numbers
Frequently asked questions
Is 2.5 or 3-ton right for a 1,500 sq ft house?
2.5 tons in a mixed climate with average insulation. The load is about 30,000 BTU/h. Older drafty envelopes and the hot, humid South both push it to 3 tons; a cool northern climate drops it to 2 tons. There is no half step between 2.5 and 3, so this is a 20% decision, not a fine adjustment.
Why does my existing 3-ton unit still not keep up on 1,500 sq ft?
Almost always airflow rather than capacity. A 3-ton system needs about 1,200 CFM, and a single undersized return grille or a crushed flex run will not pass it. Have the total external static pressure measured: gear is designed for 0.5 inches of water column and real houses routinely read 0.8 to 1.0. Fixing the duct is cheaper than another ton, and the extra ton would not have worked either.
Should I get a Manual J for a 1,500 sq ft house?
If you are buying equipment, yes, and at this size it earns its fee more often than not. A house this small sits close enough to the 2.5 and 3 ton boundary that window area and orientation regularly decide which side of it you land on. The numbers here are honest rules of thumb, good for budgeting and for catching a contractor sizing from the driveway.
How much does it cost to install AC for a 1,500 sq ft house?
A 2.5-ton-class change-out in a mixed climate often lands around $4,500–$9,000 installed when the ducts are already usable. New duct runs, panel work, SEER2 step-ups and heat-pump swaps push past it. These are labeled 2026 national ranges, not a ZIP quote.