Central Air Conditioner Size Calculator

Between 2.5 and 4 tons depending on climate, for an average house with 8 ft ceilings: about 4 tons in hot zones 1 and 2 (Florida, Texas), 3.5 tons in zone 3 (Georgia, Southern California), 3 tons in zones 4 to 6 and 2.5 tons in zone 7. A tight, well insulated house can drop a half ton; a leaky one or very sunny lot can add one. A Manual J often lands lower than any rule of thumb.

About 1,500 sq ft in a very hot climate (zone 1) up to about 2,400 sq ft in zone 7 for an average house: 1,800 sq ft in zone 3 and 2,000 in zone 4. A tight, well insulated house covers about 18% more area per ton. That is the contractor's 500 to 800 sq ft per ton rule; the real answer depends on windows, insulation and ducts.

Same idea, a tougher test. Since January 1, 2023, the DOE rates central systems with higher blower static pressure, closer to real ductwork, so SEER2 numbers run about 5% lower: the old 14 SEER minimum became 13.4 SEER2 and 15 SEER is about 14.3 SEER2. Compare SEER2 to SEER2 only.

In the North, 13.4 SEER2. In the Southeast (AL, AR, DE, FL, GA, HI, KY, LA, MD, MS, NC, OK, SC, TN, TX, VA, DC) and Southwest (AZ, CA, NV, NM), 14.3 SEER2 for units under 45,000 BTU and 13.8 SEER2 at 45,000 and up, and the Southwest also sets a minimum EER2. Split heat pumps must reach 14.3 SEER2 and 7.5 HSPF2 everywhere.

If a gas furnace heats the house, an AC plus a coil on the furnace is the cheaper swap, and in mild climates a heat pump with the furnace as backup (dual fuel) is worth a quote. If you heat with an electric air handler or furnace, get a heat pump: it cools the same and heats with far less electricity than heat strips. In zones 5 to 7, choose a cold-climate model rated to -13 F or colder and keep a backup heat kit.

A 2,000 sq ft house in a mixed climate (zone 4, 36,000 BTU load, about 1,000 full-load hours) uses about 2,500 kWh a year with a 14.3 SEER2 system: about $436 at the 17.3 cent national average, or roughly $109 a month over a four-month summer. The same house near Houston (44,000 BTU, 1,800 hours) uses about 5,540 kWh, about $958 a year at that rate.

No. An oversized AC cools the air fast and shuts off before it pulls out much moisture, so the house feels clammy, and the short on and off cycles wear the compressor. ACCA Manual S keeps an AC within about 15% over the load (heat pumps about 25%). Pick the smallest size that covers the load.

Not a standard split system: the lines are brazed, pressure tested, vacuumed and charged by a technician certified under EPA Section 608, and makers tie the warranty to a licensed install. Pre-charged systems like the MRCOOL Universal ship with a NoVac quick-connect line set, which skips the vacuum and brazing. The 240V circuit and disconnect may still need an electrician and a permit.