Answer six questions and this calculator estimates the cooling tonnage and furnace size your home needs, then points you to systems in that size. It uses the same rule-of-thumb method contractors use for a first pass — square footage, climate, insulation, ceiling height, sun exposure and occupancy — and it is honest about what it is: a starting point. The final number for a new system comes from a Manual J load calculation, which accounts for your windows, duct layout and orientation. Call (877) 843-4822 and we will run the numbers with you before you order.
How the sizing calculator works
Cooling load starts from a BTU-per-square-foot figure for your climate (hot, humid climates need more cooling per square foot than cold ones), then adjusts for insulation quality, ceiling height (more air volume to cool), sun exposure and the people in the house. The result in BTU/h is divided by 12,000 to give tonnage, rounded to the nearest half ton because that is how equipment is built: 1.5, 2, 2.5, 3, 3.5, 4 and 5 ton.
Heating load uses a separate BTU-per-square-foot figure for your winters, adjusted the same way. Gas furnaces are sold by input BTU, so the calculator divides the heating load by the furnace efficiency (AFUE) to show which furnace size covers it at 80% and at 96%.
Why right-sizing matters more than brand
An oversized air conditioner cools the air quickly and shuts off before it has pulled the humidity out, so the house feels clammy and the equipment short-cycles itself to an early death. An undersized one runs all afternoon on the hottest days and never catches up. Getting the tonnage right does more for comfort and equipment life than any efficiency rating or brand choice — which is why every complete system we sell is listed by size first.
What to do with the number
- Browse systems in your size: complete AHRI-matched systems are organized by type and tonnage.
- Read the Goodman equipment guide for configuration (upflow, horizontal, dual-fuel) and the SEER2, EER2 and HSPF2 guide for how much efficiency is worth paying for.
- Have a contractor confirm with a Manual J before the order ships — or call us and we will check the load, the duct layout and the accessories with you.
Sizing FAQ
How many square feet does a 3-ton AC cool?
Roughly 1,500 to 1,800 square feet in a moderate climate with average insulation. In a hot, humid climate with a poorly insulated house it can be closer to 1,200; in a tight, well-shaded house it can stretch past 2,000. That spread is exactly why the calculator asks about climate and insulation.
Should I go up a size to be safe?
No. Oversizing is the most common sizing mistake and it costs comfort, humidity control and equipment life. If the estimate lands between two sizes, a load calculation decides — not a bigger unit.
Is a heat pump sized the same way?
Heat pumps are sized to the cooling load in most of the country, with backup heat covering the coldest nights. In cold climates a contractor may size to the heating load or specify a cold-climate model; the dual-fuel option (heat pump plus gas furnace) sidesteps the trade-off.
What size furnace do I need?
Furnaces are sized by heating BTU input: 40,000, 60,000, 80,000, 100,000 and 120,000 BTU/h are the standard steps. The calculator shows the size that covers your heating load at 80% and 96% AFUE. An 80,000 BTU furnace is the workhorse for most 1,800 to 2,400 square foot homes in the Southeast.