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Conditioned floor area of the space.
Only the area the system will actually cool. An unconditioned garage, loft or porch is not part of the load, and including it is a common way to oversize by a third.
Summer design conditions where the building is.
Design conditions are not the record high — they are the temperature exceeded only about 1% of summer hours. Sizing for the record high guarantees oversizing for the other 99%.
Overall thermal quality of the envelope.
This one input carries what a real load calculation derives from wall, roof and floor U-values plus a measured or assumed air-change rate. It is the largest single simplification on this page.
How much solar gain the space takes.
West-facing glass in the late afternoon is the largest single peak-load driver in many houses, because it coincides with the hottest part of the day. Shading it is usually cheaper than cooling it.
People normally in the space.
Each person adds roughly 600 BTU/h of sensible and latent heat at rest. Manual J counts the first two as part of the base load; this adds for each person beyond that.
Cooking adds a substantial sensible and latent load.
A kitchen is called out separately because it adds MOISTURE as well as heat, and the two are sized for differently: equipment chosen on temperature alone can hold a space cool and leave it clammy, because it never runs long enough to dehumidify. Where the kitchen has its own extract taking the cooking load straight outside, much of this allowance leaves with it and the space behaves like an ordinary room.
Cooling capacity required (BTU/h)
22,000 BTU/h
A screening estimate, not a design. Equipment should be selected from a room-by-room load calculation (ACCA Manual J in the US, Canada's CSA F280, MCS/CIBSE in the UK, AS/NZS in Australia) before anything is ordered.
- Refrigeration tons
- 1.8 tons
- Kilowatts
- 6.33 kW
- Envelope and solar
- 21,600 BTU/h
- Occupants beyond two
- 0 BTU/h
- Kitchen
- 0 BTU/h
They open the calculator with your figures already in it
Air Conditioner Size Calculator: 21,600 BTU/h — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- ACCA Manual J (8th ed.) — residential load calculation. This page is a screening approximation of it, not an implementation.
- 1 ton of refrigeration = 12,000 BTU/h (ASHRAE Terminology)
- ACCA Manual S — equipment selection should follow the calculated load, not floor area alone
Inputs used
- Floor area
- 1080 sq ft
- Climate
- Moderate — warm summers, 27-32 °C / 80-90 °F
- Insulation and airtightness
- Average — insulated to code when built
- Sun exposure
- Average glazing and exposure
- Regular occupants
- 2
- Includes a kitchen
- No
Intermediate steps
- Refrigeration tons
- 1.8 tons
- Kilowatts
- 6.33 kW
- Envelope and solar
- 21,600 BTU/h
- Occupants beyond two
- 0 BTU/h
- Kitchen
- 0 BTU/h
Confidence note: A screening estimate, not a design. Equipment should be selected from a room-by-room load calculation (ACCA Manual J in the US, Canada's CSA F280, MCS/CIBSE in the UK, AS/NZS in Australia) before anything is ordered.
What this calculation does not cover
- Does not use window area, orientation, shading coefficient or U-value — a real Manual J does, and glazing is often the largest single term.
- Does not use a measured air-change rate. Infiltration is approximated by the insulation setting alone.
- Does not separate sensible from latent load, so it cannot tell you whether a unit will dehumidify adequately in a humid climate.
- Does not account for duct losses in unconditioned space, which can add 20-30% in a hot loft.
Add the equipment this sizes
This result is a specification — 22,000 BTU/h — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Part of a bigger job
This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations3
- ACCA Manual J (8th ed.) — residential load calculation. This page is a screening approximation of it, not an implementation.
- 1 ton of refrigeration = 12,000 BTU/h (ASHRAE Terminology)
- ACCA Manual S — equipment selection should follow the calculated load, not floor area alone
Which documents these citations point at
Standards referenced: ACCA Manual J, ACCA Manual S (Air Conditioning Contractors of America, United States).
Cite this page
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