AC tonnage calculator

How many tons of AC do I need for my house?

The short answer: about 1 ton per 600 sq ft in a mixed climate with average insulation. The longer answer is that climate, insulation, ceiling height, and sun exposure can shift that by 30 to 50 percent. The calculator above runs all of those factors. Here is the quick-reference chart for a typical 8-foot ceiling, average insulation, mixed climate:

• 600 sq ft: 1 ton (12,000 BTU)
• 900 sq ft: 1.5 tons (18,000 BTU)
• 1,200 sq ft: 2 tons (24,000 BTU)
• 1,500 sq ft: 2.5 tons (30,000 BTU)
• 1,800 sq ft: 3 tons (36,000 BTU)
• 2,100 sq ft: 3.5 tons (42,000 BTU)
• 2,400 sq ft: 4 tons (48,000 BTU)
• 3,000 sq ft: 5 tons (60,000 BTU)

Residential AC units only come in those eight sizes. There is no such thing as a 2.7 ton Carrier or a 3.3 ton Trane. If your load lands between two sizes, round down. A slightly undersized unit runs longer and pulls more humidity, which feels better than an oversized unit short-cycling cold air.

How much does a 2 to 5 ton AC unit cost installed?

Central AC installation in the U.S. currently averages $5,800 to $9,500 for a mid-tier 3 ton system. Goodman and Rheem sit on the lower end of those ranges, mid-line Carrier and Lennox in the middle, Trane and American Standard high-SEER2 on the upper end. Premium 16 to 20 SEER2 units can push 5 ton installs past $14,000. Here is what to expect for each size, fully installed including labor:

• 1.5 ton AC unit installed: $4,200 to $7,000
• 2 ton AC unit installed: $4,800 to $8,000
• 2.5 ton AC unit installed: $5,200 to $8,800
• 3 ton AC unit installed: $5,800 to $9,500
• 3.5 ton AC unit installed: $6,500 to $10,500
• 4 ton AC unit installed: $7,200 to $11,500
• 5 ton AC unit installed: $8,000 to $14,000

Premium variable-speed and high SEER2 efficiency add $2,000 to $5,000 to those prices. Federal HVAC tax credits cover up to $600 of qualifying SEER2 16+ central AC. Heat pumps qualify for up to $2,000, plus state and utility rebates that often stack on top. Always get three quotes before signing. Ranges based on current HomeGuide, Angi, and PickHVAC installed-cost data.

Why climate zone changes the AC tonnage you need

The same 2,000 sq ft house needs very different AC tonnage in different climates. In Houston or Miami (Zone 1 or 2), you might need 4 tons. In Boston or Seattle (Zone 5 or 6), the same house often only needs 2.5 to 3 tons. The DOE splits the U.S. into seven climate zones based on outdoor design temperature, which is the hottest 1 percent of summer hours.

Hot humid zones run 18 to 25 percent above the national baseline because of latent load (the AC has to wring water out of the air on top of cooling it). Hot dry zones like Phoenix run closer to 10 to 15 percent above baseline because the air is already dry. Cool northern zones run 8 to 18 percent below baseline. This is why a contractor who sizes only by square footage almost always picks the wrong tonnage in your climate.

Square feet per ton chart and the contractor rule of thumb

HVAC contractors use a quick rule of thumb: 400 to 600 sq ft per ton, depending on the climate. New homes with good insulation in mild climates can stretch to 700 sq ft per ton. Old homes in hot southern states drop to 350 to 450 sq ft per ton. The calculator on this page picks the right ratio for your specific situation instead of using a single average.

Here is the sq-ft-per-ton range by climate:

• Zone 1 to 2 (hot humid): 400 to 500 sq ft per ton
• Zone 3 (warm): 500 to 600 sq ft per ton
• Zone 4 (mixed): 550 to 650 sq ft per ton
• Zone 5 to 7 (cool to cold): 600 to 750 sq ft per ton

Carrier, Trane, Goodman, Lennox: does AC brand affect tonnage?

The tonnage you need is a math problem. It does not depend on what brand of AC you buy. A 3 ton Goodman pulls the same heat out of your house as a 3 ton Carrier. What changes with brand is build quality, warranty coverage, and how much you pay. Goodman and Rheem are the value plays: solid units at lower prices, usually 10-year parts warranty. Carrier and Trane are the premium brands: slightly better efficiency, quieter compressors, and longer real-world life on the high SEER2 lines. Lennox sits in the middle. Daikin and Mitsubishi dominate the mini split market and have moved into central AC with strong inverter-driven systems.

Whichever brand you pick, the tonnage stays the same. Do not let an HVAC contractor talk you into a bigger unit because of brand. Show them the tonnage from this calculator and ask why they would deviate from it.

What happens when you buy the wrong AC tonnage

Oversized AC is the most common HVAC mistake in America. A unit that is too big short-cycles: cools the room in three minutes, shuts off, restarts ten minutes later. The compressor never runs long enough to pull humidity out of the air, so the house feels clammy even at 72 degrees. Energy bills run 25 to 35 percent higher, and the unit wears out 30 to 50 percent faster.

Undersized AC is less common but worse on hot days. The unit runs nonstop, never quite gets the house to setpoint, and the compressor overheats. If you are choosing between two sizes, round down rather than up. A slightly undersized 3 ton handles a borderline 3.2 ton load better than a 3.5 ton would, and the cost is $500 to $1,500 less.

When to get a Manual J load calculation

For any permitted central AC install, your HVAC contractor should run a Manual J load calculation. That is the industry standard from ACCA (Air Conditioning Contractors of America). The tonnage calculator on this page uses the same inputs Manual J uses and gets you within 0.5 tons of the result. Use it to sanity-check a contractor quote before you sign. If the contractor refuses to share their Manual J in writing, get another quote.