HVAC Sizing Reference
BTU Per Square Foot Chart
Rule-of-thumb cooling and heating BTU per square foot by climate zone, and the tons-to-BTU conversion. A fast starting point, not a substitute for a Manual J load calculation.
BTU Per Square Foot by Climate Zone
| Climate zone | Example cities | Cooling (BTU/sqft) | Heating (BTU/sqft) |
|---|---|---|---|
| Zone 1: Hot Humid | Miami, Key West, Honolulu | 25 | 10 |
| Zone 2: Hot | Houston, Phoenix, Tampa, New Orleans | 22 | 18 |
| Zone 3: Warm | Atlanta, Dallas, Memphis, Charlotte | 20 | 25 |
| Zone 4: Mixed | Baltimore, Nashville, St. Louis, Richmond | 18 | 30 |
| Zone 5: Cool | Chicago, Denver, Boston, Pittsburgh | 16 | 35 |
| Zone 6: Cold | Minneapolis, Milwaukee, Burlington, Helena | 14 | 40 |
| Zone 7: Very Cold | Fairbanks, Duluth, International Falls | 12 | 50 |
Tons to BTU Conversion & Square Footage
| System size (tons) | BTU/hr | Approx. sq ft (mixed climate) |
|---|---|---|
| 1.5 | 18,000 | 600 - 1,000 |
| 2 | 24,000 | 900 - 1,300 |
| 2.5 | 30,000 | 1,200 - 1,600 |
| 3 | 36,000 | 1,500 - 2,000 |
| 3.5 | 42,000 | 1,800 - 2,300 |
| 4 | 48,000 | 2,100 - 2,700 |
| 5 | 60,000 | 2,600 - 3,300 |
How to Estimate, and Why Manual J Wins
The rule of thumb is simple: BTU = floor area (sq ft) × BTU per square foot for your climate zone, then divide by 12,000 to get tons. For a 1,600 sq ft home in a warm climate (20 BTU/sqft): 1,600 × 20 = 32,000 BTU, which is 2.7 tons, so a 2.5 or 3-ton unit. It gets you in the ballpark in ten seconds.
But it is only a ballpark. Two identical-size homes can differ by a full ton based on insulation, window area and type, orientation, air sealing, ceiling height, and occupancy. Sizing from square footage alone usually oversizes the system, and an oversized AC short cycles: it cools the air fast without running long enough to pull humidity, leaving the house cold and clammy. ACCA Manual J is the code-recognized method because it accounts for all of those factors. Use this chart to sanity-check a quote, not to pick final equipment.
Frequently Asked Questions
How many BTU per square foot to cool a house?
As a rule of thumb, cooling runs about 22 to 25 BTU per square foot in hot climates (zones 1 to 2), 16 to 20 in mixed climates (zones 3 to 5), and 12 to 14 in cold climates (zones 6 to 7). The exact figure depends on insulation, windows, and orientation, so a Manual J calculation is the accurate method.
How many BTU are in a ton of cooling?
One ton of air conditioning equals 12,000 BTU per hour. So a 2-ton system is 24,000 BTU/hr, 3-ton is 36,000, 4-ton is 48,000, and 5-ton is 60,000 BTU/hr. The term comes from the cooling equal to melting one ton of ice in 24 hours.
How many tons of AC do I need for 2,000 square feet?
As a rough starting point, a 2,000 square foot home needs about 3 tons of cooling in a mixed climate (2,000 x 18 BTU/sqft = 36,000 BTU = 3 tons). Hot climates push it to 3.5 or 4 tons, cold climates toward 2.5. Always confirm with a Manual J load calculation before buying equipment.
How many BTU to cool 1,000 square feet?
About 18,000 to 22,000 BTU as a rule of thumb in a mixed to warm climate (1,000 sqft x 18 to 22 BTU/sqft), which is roughly a 1.5 to 2 ton system. A well-insulated home in a cool climate may need only 14,000 to 16,000 BTU.
Is BTU per square foot accurate for sizing an air conditioner?
No, it is only a rough starting point. Sizing from a per-square-foot rule of thumb often oversizes the system, which causes short cycling and poor humidity control. ACCA Manual J, which accounts for insulation, windows, orientation, air infiltration, and internal loads, is the code-recognized sizing method.
Related Calculators & Charts
BTU / Load Calculator
The Manual J style version: enter climate, insulation, windows, and duct location for a real cooling and heating load.
Tonnage From Model Number
Decode the tonnage of an existing condenser or air handler from its model number.
Superheat & Subcooling Calculator
Once it is installed and sized, verify the charge with PT interpolation and the four-quadrant diagnostic.
Ballpark done. Get the real load.
Square footage is the starting point; the BTU load calculator runs the Manual J style math by climate zone, insulation, windows, and duct location so you size the system to the house, not the nameplate.