How many BTU per square foot do you need?
There is no single BTU per square foot figure that fits every house. The common cooling estimate that the US Department of Energy (DOE) cites works out to 24 to 30 BTU/h per square foot, and Bryant publishes 30 to 60 for heating, by climate. Both are starting points, and both sources say a load calculation gives the right size.
How many BTU per square foot does central air conditioning need?
DOE cites a common estimate of one ton of cooling per 400 to 500 square feet. That works out to 24 to 30 BTU/h per square foot. DOE says that estimate fails to take into account local climate and the efficiency of a house. It says one ton can condition 800 to 1,000 square feet of a very efficient house, or 12 to 15 BTU/h per square foot.
| Rule | Square feet per ton | BTU/h per square foot |
|---|---|---|
| Common estimate | 400 to 500 | 24 to 30 |
| Very efficient house | 800 to 1,000 | 12 to 15 |
One ton of cooling is 12,000 BTU/h. The last column divides that by the square feet per ton.
DOE’s Building America guide treats homes with more than 1,000 square feet per ton as low-load homes.
How many BTU per square foot does heating need?
Bryant, a furnace maker, publishes 30 to 60 BTU/h per square foot, depending on climate. Bryant says furnace size is measured in BTUs, which indicate how much heat a system can produce.
| Climate | BTU/h per square foot |
|---|---|
| Warm: South and Southwest | 30 to 35 |
| Moderate: Midwest and Mid-Atlantic | 40 to 50 |
| Cold: Northeast and northern Midwest | 50 to 60 |
Bryant calls its quick calculation a helpful starting point. It says a professional load calculation is the best way to determine the right size.
How many BTU per square foot does a room air conditioner need?
It depends on room size, from 33 to 50 BTU/h per square foot in the smallest rooms to 14 to 17 in the largest. These figures are worked out from ENERGY STAR’s chart. The chart runs from 5,000 BTU/h for 100 up to 150 square feet to 34,000 BTU/h for 2,000 up to 2,500.
| Room floor area (sq ft) | Capacity needed (BTU/h) | BTU/h per square foot |
|---|---|---|
| 100 up to 150 | 5,000 | 33 to 50 |
| 150 up to 250 | 6,000 | 24 to 40 |
| 250 up to 300 | 7,000 | 23 to 28 |
| 300 up to 350 | 8,000 | 23 to 27 |
| 350 up to 400 | 9,000 | 23 to 26 |
| 400 up to 450 | 10,000 | 22 to 25 |
| 450 up to 550 | 12,000 | 22 to 27 |
| 550 up to 700 | 14,000 | 20 to 25 |
| 700 up to 1,000 | 18,000 | 18 to 26 |
| 1,000 up to 1,200 | 21,000 | 18 to 21 |
| 1,200 up to 1,400 | 23,000 | 16 to 19 |
| 1,400 up to 1,500 | 24,000 | 16 to 17 |
| 1,500 up to 2,000 | 30,000 | 15 to 20 |
| 2,000 up to 2,500 | 34,000 | 14 to 17 |
ENERGY STAR words each row as “X up to Y” square feet. The last column divides each capacity by the top and the bottom of its area range. The chart assumes an 8 foot ceiling.
ENERGY STAR says to cut the capacity by 10 percent for a heavily shaded room and add 10 percent for a very sunny one. Add 600 BTU/h for each person beyond two and 4,000 BTU/h for a kitchen.
ENERGY STAR says an oversized room air conditioner costs more to buy, wastes energy and does not cool better. Use the BTU calculator for a room or the mini-split sizing calculator for ductless units.
How many BTU does a whole house need by square footage?
For 2,000 square feet, the tables give 48,000 to 60,000 BTU/h of cooling and 60,000 to 120,000 BTU/h of heat. They apply the DOE and Bryant figures to five floor areas. They give ranges, not loads. Both are rounded to the nearest 1,000 BTU/h.
| Cooling capacity (BTU/h) | ||
|---|---|---|
| Floor area (sq ft) | Common estimate | Very efficient house |
| 1,000 | 24,000 to 30,000 | 12,000 to 15,000 |
| 1,500 | 36,000 to 45,000 | 18,000 to 23,000 |
| 2,000 | 48,000 to 60,000 | 24,000 to 30,000 |
| 2,500 | 60,000 to 75,000 | 30,000 to 38,000 |
| 3,000 | 72,000 to 90,000 | 36,000 to 45,000 |
| Heat output (BTU/h) | |||
|---|---|---|---|
| Floor area (sq ft) | Warm climate | Moderate climate | Cold climate |
| 1,000 | 30,000 to 35,000 | 40,000 to 50,000 | 50,000 to 60,000 |
| 1,500 | 45,000 to 53,000 | 60,000 to 75,000 | 75,000 to 90,000 |
| 2,000 | 60,000 to 70,000 | 80,000 to 100,000 | 100,000 to 120,000 |
| 2,500 | 75,000 to 88,000 | 100,000 to 125,000 | 125,000 to 150,000 |
| 3,000 | 90,000 to 105,000 | 120,000 to 150,000 | 150,000 to 180,000 |
Why doesn’t one BTU-per-square-foot number work?
A house’s load depends on more than its floor area. DOE says requirements depend on house size, insulation, window performance, heating and cooling usage, and local climate. Bryant adds that insulation, ceiling height and air leakage can shift your exact needs.
- Ducts. DOE’s Building America guideline says loads are more sensitive to duct leakage and duct insulation when ducts run outside conditioned space.
- Ceiling height. ENERGY STAR calculates its room chart for an 8 foot ceiling.
- Newer houses. A new 3,000 square foot high-performance home might be adequately served by one 3 ton unit with zone dampers, DOE’s Building America guide says. An older two-story home of that size might have required two 3 ton units.
DOE’s load calculation guideline calculated two houses of 2,223 square feet built to the 2009 International Energy Conservation Code. The Chicago house had a heating load of 41,700 BTU/h and the Orlando house 23,600 BTU/h. Their cooling loads were 20,600 and 20,700 BTU/h. The 400 to 500 square feet per ton rule gives 53,000 to 67,000 BTU/h for that area.
The guideline says many HVAC companies rely on a “400 square feet per ton” rule. It says a contractor may manipulate the inputs to land near it.
A house has a heating load and a cooling load, and one figure cannot give both. The Chicago house needs about 2 times as much heating as cooling. DOE also says the loads in energy-efficient homes are often so small that they fall outside manufacturers’ range of capacities.
What should I use instead of BTU per square foot?
Use a Manual J load calculation. DOE says your contractor should use Manual J from the Air Conditioning Contractors of America (ACCA) to calculate the proper size of HVAC equipment. A DOE education page says rules of thumb are too often used to size comfort systems, which results in excessively oversized systems. Read what a Manual J load calculation is, or turn a result into a size with what size AC unit you need.
Questions and answers
How many BTU per square foot do I need?
There is no single figure. The common cooling estimate DOE cites works out to 24 to 30 BTU/h per square foot, and Bryant publishes 30 to 60 BTU/h per square foot for heating, by climate. DOE and Bryant both say a load calculation gives the right size.
How many BTU does a 2,000 square foot house need?
At the common cooling estimate, 48,000 to 60,000 BTU/h of cooling. At DOE’s very efficient figure, 24,000 to 30,000. Bryant’s heating ranges give 60,000 to 70,000 BTU/h in warm climates, 80,000 to 100,000 in moderate and 100,000 to 120,000 in cold. These are ranges, not loads.
Is 400 square feet per ton a good rule?
DOE says the 400 to 500 square feet per ton estimate fails to take into account local climate and the efficiency of a house. In DOE’s example, two houses of 2,223 square feet had cooling loads of 20,600 and 20,700 BTU/h. That rule gives 53,000 to 67,000 BTU/h for that area.
How many BTU per square foot does a room air conditioner need?
ENERGY STAR’s chart gives 5,000 BTU/h for a room of 100 up to 150 square feet and 18,000 BTU/h for 700 up to 1,000 square feet. That works out to 33 to 50 and 18 to 26 BTU/h per square foot. The chart assumes an 8 foot ceiling.
Sources
- US Department of Energy, Consumer Guide to Home Heating and Cooling (government): https://www.energy.gov/sites/default/files/2021-08/ES-HomeHeatingandCooling_081221.pdf
- DOE Building America Solution Center, Air Conditioning (government): https://basc.pnnl.gov/resource-guides/air-conditioning
- DOE Building America, Strategy Guideline: Accurate Heating and Cooling Load Calculations (NREL/SR-5500-51603, June 2011), DOE-hosted PDF (government): https://www1.eere.energy.gov/buildings/publications/pdfs/building_america/hvac_load_calc.pdf
- ENERGY STAR, Room Air Conditioners (buying guidance and sizing chart) (government): https://www.energystar.gov/products/room_air_conditioners
- DOE Building Science Education Solution Center, Proper Sizing of HVAC Systems (government): https://bsesc.energy.gov/energy-basics/hvac-proper-sizing-hvac-systems
- ACCA, Manual J Residential Load Calculation (technical manual page) (standards body): https://www.acca.org/standards/technical-manuals/manual-j
- Bryant, What Size Furnace Do I Need? BTU Sizing Guide (manufacturer): https://www.bryant.com/en/us/products/gas-furnaces/what-size-furnace-do-i-need/
More guides
- What size AC unit do I need?Sizes from 1.5 to 5 tons, what oversizing does, and how Manual J and Manual S set the size.
- Manual J load calculation: what it is and how to check oneWhat the calculation finds, the inputs it needs, where codes require it and what to ask a contractor for.
- Rating plate: where to find the model and serial numberWhere the plate is on each kind of equipment, what its lines mean, and how it differs from the EnergyGuide label.
The facts in this guide rest on 49 passages in the sources above. Each passage was found in its document on October 5, 2026. Method and sources.