What Size AC for a 3,000 Square Foot House?
Cooling size
5.5 tons
3,000 square feet, 8 foot ceilings, climate zone 4, average sun, five 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.
Above 5 tons you are past ordinary residential split system territory. That is usually two systems or a zoned system rather than one large condenser, and it is another reason to get the load calculation done properly.
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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 area3000 sq ft
- Ceiling height8 ft
- Climate zoneZone 4, mixed, mid Atlantic and the lower Midwest
- Sun exposureAverage
- People living there5 each
- Kitchen inside the conditioned spaceYes
Cooling size5.5 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.
Above 5 tons you are past ordinary residential split system territory. That is usually two systems or a zoned system rather than one large condenser, and it is another reason to get the load calculation done properly.
| Cooling load | 65,800 BTU/hr |
|---|---|
| That is | 5.48 tons12,000 BTU makes a ton |
| Equipment size to shop for | 5.5 tonnearest half ton step |
| Cooling per square foot | 22 BTU |
| Heating output needed | 135,000 BTU/hr |
| Furnace input, 80% AFUE | 168,750 BTU/hr |
| Furnace input, 95% AFUE | 142,105 BTU/hr |
The material list this produces
| Condenser, tons | 6 |
|---|---|
| Matched air handler or coil, tons | 6 |
| 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 | 6 tons | 90,000 BTU/hr |
| Zone 2 | 6 tons | 105,000 BTU/hr |
| Zone 3 | 5.5 tons | 120,000 BTU/hr |
| Zone 4 | 5.5 tons | 135,000 BTU/hr |
| Zone 5 | 5 tons | 150,000 BTU/hr |
| Zone 6 | 5 tons | 165,000 BTU/hr |
| Zone 7 | 5 tons | 180,000 BTU/hr |
What else matters here
Sixty five thousand eight hundred BTU is 5.48 tons, and that is the point where the answer stops being a single number. Residential equipment tops out at 5 tons, so a house this size is normally two systems: a 3 ton and a 2.5 ton, or a 3 and a 3, one per floor.
Two systems is not just a workaround for the size limit. It is the right answer for comfort in a big house, because the upstairs and the downstairs of a 3,000 square foot home have genuinely different loads at the same moment on a summer afternoon, and one thermostat cannot serve both.
It also changes what a failure costs. One system down in July on a two system house is uncomfortable. One system down on a single system house is a hotel bill.
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 3,000 square feet?
About 65,800 in a mixed climate, which is 5.48 tons. Since residential equipment stops at 5 tons, that is normally split across two systems.
Should a 3,000 square foot house have two AC units?
Usually yes, and not only because of the size limit. Two systems let each floor run on its own thermostat, which is the only reliable fix for a hot upstairs, and they mean one breakdown does not take the whole house out.
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.