What Size AC for a 1,000 Square Foot House?
Cooling size
2 tons
1,000 square feet, 8 foot ceilings, climate zone 4, average sun, two people, kitchen inside.
This is a rule of thumb and it is not a load calculation. The real answer is a Manual J, which counts your windows, your insulation, your infiltration and which way the house faces, and a contractor should run one before anybody orders equipment. Use this number to sanity check a quote, not to place an order.
Oversizing is the classic mistake and it is worse than being slightly small. A unit with too much capacity satisfies the thermostat in a few minutes and shuts off, so it never runs long enough to pull water out of the air, and the house ends up cold and clammy with the compressor short cycling itself to an early grave.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Conditioned floor area1000 sq ft
- Ceiling height8 ft
- Climate zoneZone 4, mixed, mid Atlantic and the lower Midwest
- Sun exposureAverage
- People living there2 each
- Kitchen inside the conditioned spaceYes
Cooling size2 tons
This is a rule of thumb and it is not a load calculation. The real answer is a Manual J, which counts your windows, your insulation, your infiltration and which way the house faces, and a contractor should run one before anybody orders equipment. Use this number to sanity check a quote, not to place an order.
Oversizing is the classic mistake and it is worse than being slightly small. A unit with too much capacity satisfies the thermostat in a few minutes and shuts off, so it never runs long enough to pull water out of the air, and the house ends up cold and clammy with the compressor short cycling itself to an early grave.
| Cooling load | 24,000 BTU/hr |
|---|---|
| That is | 2 tons12,000 BTU makes a ton |
| Equipment size to shop for | 2 tonnearest half ton step |
| Cooling per square foot | 24 BTU |
| Heating output needed | 45,000 BTU/hr |
| Furnace input, 80% AFUE | 56,250 BTU/hr |
| Furnace input, 95% AFUE | 47,368 BTU/hr |
The material list this produces
| Condenser, tons | 2 |
|---|---|
| Matched air handler or coil, tons | 2 |
| Line set, ft | 25 |
| Equipment pad, each | 1 |
| Disconnect and whip, each | 1 |
| Programmable thermostat, each | 1 |
Climate zone compared
The same house sizes differently by climate, and not in the direction people expect. Cooling load falls as you go north while heating load climbs, so a Minnesota house needs a smaller air conditioner and a much bigger furnace than a Florida one.
| Climate zone | Cooling size | Heating output needed |
|---|---|---|
| Zone 1 | 2.5 tons | 30,000 BTU/hr |
| Zone 2 | 2 tons | 35,000 BTU/hr |
| Zone 3 | 2 tons | 40,000 BTU/hr |
| Zone 4 | 2 tons | 45,000 BTU/hr |
| Zone 5 | 2 tons | 50,000 BTU/hr |
| Zone 6 | 2 tons | 55,000 BTU/hr |
| Zone 7 | 2 tons | 60,000 BTU/hr |
What else matters here
Twenty four thousand BTU, which is exactly 2 tons, and 2 tons is a size you can buy. That is the easy case: no rounding argument, no half ton to think about.
It works out at 24 BTU a square foot, a touch above the 20 base because the kitchen and the occupants are in there. A house this size is usually a small ranch, a cottage or a condo, and the thing most likely to move the real number is glass: a wall of west facing windows on a 1,000 square foot house is a much larger fraction of the load than the same wall on a 3,000 square foot one.
On the heating side it is 45,000 BTU of output, which an 80 percent furnace delivers from a 56,250 BTU input and a 95 percent one from 47,368. Furnace labels usually quote input, so read a quote carefully before comparing two of them.
What this calculator assumes
- This is the square foot method, the same rule of thumb behind every free sizing chart: 20 BTU per square foot of cooling as the base, scaled for ceiling height, climate zone and sun, plus 600 BTU for each person over two and 4,000 for a kitchen.
- Heating is figured at 30 to 60 BTU per square foot depending on zone, which is output at the register. Furnace input is higher, because an 80 percent furnace throws a fifth of the gas up the flue.
- Equipment is sold in half ton steps up to 5 tons, so the number to shop with is the rounded one, not the raw one.
Questions people ask
How many BTU for 1,000 square feet?
About 24,000 for cooling in a mixed climate, which is 2 tons. Hotter zones push it up and colder ones pull it down.
What is a ton of cooling?
12,000 BTU per hour. It comes from the ice trade, the heat needed to melt one ton of ice over twenty four hours. Residential split systems are sold in half ton steps from one and a half up to five, so the only sizes you can actually buy are 18,000, 24,000, 30,000 and so on.
Is this the same as a Manual J?
No. A Manual J counts the actual windows and which way they face, the insulation in the walls and the attic, how tight the envelope is, the duct losses and the local design temperature. Two houses of identical size can be a ton and a half apart on that calculation. Use this figure to check whether a quote is in the right range, then have the load calculation done before anything is ordered.
The btu and ac size calculator takes any dimensions you like and hands back the same list.