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AC size · 1,500 sq ft
What size AC for a 1,500 sq ft house
A 1,500 sq ft house needs anywhere from 1 ton to 3.5 tons of cooling in the 14 climates below. The low end is a tight 2015 house in San Francisco, CA and the high end is a 1985 house with attic ducts in Phoenix, AZ. The 400 to 600 sq ft per ton rule gives 2.5 to 3.75 tons for all of them. Check your zone first.
Run your own house in the calculator. It starts with a 1,500 sq ft single-story house in Atlanta, GA, built in 1985 with ducts in the attic.
- Type the 5-digit ZIP of the job. The calculator looks up the climate zone and its design temperatures.
- Enter the conditioned floor area, stories and year built. The form starts at 1,500 sq ft.
- Pick air tightness, foundation and window type, and check the box if the ducts run through an unconditioned attic.
- Read the cooling load and tonnage, then find the row for your climate zone in the table below to see how the envelope changes the size.
Example result for the default inputs
ZIP 30303 · Fulton County, GA · IECC zone 3A · elevation 1,001 ft · design 95°F DB / 76°F WB cooling, 18°F heating
Cooling load
23,017BTU/h
≈ 2 ton (nearest 0.5) · SHR 0.93
Heating load
33,341BTU/h
- Furnace input bin 60,000 BTU/h at 80% AFUE
- Heat pump 48,000 BTU/h at 47°F (35,040 at design temp)
Load breakdown by component
| Component | Cooling | Heating |
|---|---|---|
| Transmission (walls, ceiling, floor, glass, doors) | 6,735 | 21,827 |
| Solar through glass | 9,730 | - |
| Infiltration | 1,769 | 5,957 |
| Internal gains (people, appliances) | 2,490 | - |
| Ducts in unconditioned attic | 2,293 | 5,557 |
- These design temperatures are the worst case for the IECC climate zone. BuildSolver estimates ZIP-level values can differ by 2-8°F.
- These are preliminary design conditions. For a permit load, take the design temperatures from ASHRAE Handbook - Fundamentals 2021, Chapter 14.
For estimation purposes only. Consult a licensed engineer for final designs.
Room-by-room Manual J and branded PDF reports · Pro plan
How the tonnage in the table is calculated
Each of the 28 cells in the table is its own run of the BuildSolver load engine on a 1,500 sq ft house, using the whole-house Speed Sheet simplification of ACCA Manual J 8th Edition. The AC size hub has the full method and every floor area side by side.
- House geometry
footprint = 1,500 / 1 = 1,500 sq ft; side = 39 ftThe engine models a square single-story footprint with 8 ft ceilings, which gives about 1,239 sq ft of gross wall and 1,500 sq ft of ceiling under the attic.- Tonnage
tons = Q_cool / 12,000, rounded to the nearest 0.5Loads are rounded to the nearest half ton, which puts this floor area between 1 ton and 3.5 tons.- Square feet per ton
sq ft per ton = 1,500 / (Q_cool / 12,000)Computed from the unrounded load. Across this table one ton covers 434 to 1,951 sq ft.
AC size for a 1,500 sq ft house in 14 climate zones
Each row is the same 1,500 sq ft single-story house on a slab with 3 occupants and glass at 15% of floor area. Only the climate zone and the envelope change. The first house column is a 1985 build with average air sealing and ducts in a vented attic. The second is a 2015 build with a tight envelope and ducts inside conditioned space. Tons are rounded to the nearest half ton. Each cell also shows the load in BTU/h and how many square feet one ton covers.
| Zone | Reference city | Cooling design | 1985 house, attic ducts | 2015 house, ducts inside |
|---|---|---|---|---|
| 1A | Miami, FL | 92°F | 2.5 tons31,793 BTU/h · 566 sq ft/ton | 1.5 tons15,889 BTU/h · 1,133 sq ft/ton |
| 2A | Houston, TX | 96°F | 3 tons33,980 BTU/h · 530 sq ft/ton | 1.5 tons17,010 BTU/h · 1,058 sq ft/ton |
| 2B | Phoenix, AZ | 110°F | 3.5 tons41,456 BTU/h · 434 sq ft/ton | 1.5 tons20,839 BTU/h · 864 sq ft/ton |
| 3A | Atlanta, GA | 95°F | 2 tons23,017 BTU/h · 782 sq ft/ton | 1.5 tons15,192 BTU/h · 1,185 sq ft/ton |
| 3B | Las Vegas, NV | 100°F | 2 tons24,666 BTU/h · 730 sq ft/ton | 1.5 tons16,423 BTU/h · 1,096 sq ft/ton |
| 3C | San Francisco, CA | 84°F | 1.5 tons16,190 BTU/h · 1,112 sq ft/ton | 1 ton10,713 BTU/h · 1,680 sq ft/ton |
| 4A | St. Louis, MO | 92°F | 1.5 tons20,847 BTU/h · 863 sq ft/ton | 1 ton13,771 BTU/h · 1,307 sq ft/ton |
| 4B | Albuquerque, NM | 95°F | 1.5 tons20,957 BTU/h · 859 sq ft/ton | 1 ton14,016 BTU/h · 1,284 sq ft/ton |
| 4C | Seattle, WA | 84°F | 1 ton13,622 BTU/h · 1,321 sq ft/ton | 1 ton9,225 BTU/h · 1,951 sq ft/ton |
| 5A | Chicago, IL | 91°F | 1.5 tons20,266 BTU/h · 888 sq ft/ton | 1 ton13,113 BTU/h · 1,373 sq ft/ton |
| 5B | Denver, CO | 93°F | 1.5 tons19,913 BTU/h · 904 sq ft/ton | 1 ton13,007 BTU/h · 1,384 sq ft/ton |
| 6A | Minneapolis, MN | 90°F | 1.5 tons18,456 BTU/h · 975 sq ft/ton | 1 ton12,185 BTU/h · 1,477 sq ft/ton |
| 6B | Billings, MT | 92°F | 1.5 tons18,337 BTU/h · 982 sq ft/ton | 1 ton12,222 BTU/h · 1,473 sq ft/ton |
| 7 | Duluth, MN | 86°F | 1.5 tons15,186 BTU/h · 1,185 sq ft/ton | 1 ton10,142 BTU/h · 1,775 sq ft/ton |
Only 3 of the 28 engine results land inside the rule-of-thumb range of 2.5 to 3.75 tons, the 1985 house in zones 1A, 2A and 2B.
In Phoenix, AZ the 1985 house with attic ducts needs 3.5 tons and the tight 2015 house with its ducts inside needs 1.5 tons, 2 tons apart on the same floor area.
In Seattle, WA even the older house rounds to 1 ton or less, on cooling loads of 13,622 BTU/h. Check the smallest ducted condenser in the line you carry against those loads, and price a ductless or variable-speed unit whose rated capacity range covers them.
The highlighted Atlanta row is the calculator's starting point. There the 1985 house needs 23,017 BTU/h, or 2 tons, and a heating load of 33,341 BTU/h at 18°F. Built tight in 2015 with the ducts inside, the same house needs 1.5 tons. A 500 sq ft per ton quote would put 3 tons on both. Size each house from its own row, then check the existing ducts and registers before you write the quote.
Standards and data sources
- ACCA Manual J 8th Edition - residential load procedure. The tables use its whole-house Speed Sheet simplification, which gives a single load for the whole house.
- ACCA Manual S - equipment selection against the Manual J load, including the 115% limit on cooling capacity for a single-speed unit. Selection is a separate step and part of the Pro plan.
- IECC 2021 climate zones (PNNL county map) - ZIP to county to climate zone. The zone sets the design temperatures, solar factor and envelope defaults for each row.
What the table leaves out
- Every row is one standard 1,500 sq ft house. On a real job, insulation, glass, orientation and air leakage move the load, and in this table the 1985 and 2015 builds in Phoenix, AZ already land 2 tons apart.
- Each row uses the worst-case design temperature of its IECC climate zone, from 84°F in the San Francisco zone to 110°F in the Phoenix zone. BuildSolver estimates ZIP-level values can differ by 2-8°F, and ASHRAE Handbook - Fundamentals 2021, Chapter 14, lists the city values.
- Single story on a slab. A crawlspace or basement changes the floor loss, and a vaulted great room adds wall and volume the page does not model.
- Whole-house load only. Room-by-room Manual J and Manual S equipment selection are part of the Pro plan.
Common sizing mistakes on a 1,500 sq ft house
- Quoting 4 tons because the house is 1,500 sq ft. The 400 sq ft per ton rule gives 3.75 tons, which a quote rounds to 4 tons. In the St. Louis, MO row the engine puts the 1985 house at 1.5 tons and the 2015 house at 1 ton.
- Reusing the tonnage from a job in another market. The same 1985 house with attic ducts needs 1 ton in Seattle, WA and 3.5 tons in Phoenix, AZ.
- Sizing off the nameplate of the unit coming out. It may have been picked by rule of thumb, and matching it repeats whatever oversizing the last installer chose.
- Letting the heating load set the AC. In Duluth, MN the 1985 house needs 55,624 BTU/h of heat and 1.5 tons of cooling. Pick the furnace and the AC from their own loads.
What to check on a 1,500 sq ft house
On a replacement call, a 1,500 sq ft house is usually a three-bedroom, two-bath single story from the 1980s or 1990s. If the unit coming out is 3 tons, that is exactly what a 500 sq ft per ton rule gives on this floor area. Compare it with the row for your zone in the table.
- Ask what changed since the last install. Replacement windows, blown-in attic insulation or a new roof with a radiant barrier can change the load on a house this size. Enter the current windows and insulation in the calculator to see by how much.
- On a 1,500 sq ft single story the attic is large relative to the floor, so ceiling insulation matters more than on a two-story house of the same area.
- If the old unit is 3.5 tons and the load says 2, check the supply registers before you downsize. At 400 CFM per ton, registers picked for about 1,400 CFM can throw weakly at the 800 CFM a 2-ton unit moves, and rooms at the end of long runs feel it first.
Questions about AC size for 1,500 sq ft
What size AC do I need for a 1,500 sq ft house?
Climate and construction decide it. In the table on this page the answer runs from 1 ton in San Francisco, CA to 3.5 tons in Phoenix, AZ. In Chicago, IL the same house comes out at 1.5 tons as a 1985 build and 1 ton as a 2015 build. Enter your ZIP and the house details in the calculator for your own number.
How many BTU does a 1,500 sq ft house need for cooling?
The cooling loads in the table run from 9,225 to 41,456 BTU/h. Per square foot that is 6.2 to 27.6 BTU/h, so no single BTU per square foot number fits a house this size. Run the actual house in the calculator above for its number.
Is a 4-ton AC too big for a 1,500 sq ft house?
ACCA Manual S limits a single-speed cooling unit to 115% of the Manual J load. By that limit a 4-ton single-speed unit is oversized for every house on this page, including the 1985 house in Phoenix, AZ at 41,456 BTU/h.
What size furnace goes with a 1,500 sq ft house?
The heating loads in the same runs go from 9,951 to 55,624 BTU/h, the highest for the 1985 house in Duluth, MN. With the engine's AFUE default for the year built, those loads call for furnace inputs from the 40,000 to the 80,000 BTU/h bin. The furnace size calculator shows the heating result for a single ZIP.
Why does a 1,500 sq ft house need a different size in Phoenix and Seattle?
Design temperature and solar load. The table uses 110°F for the Phoenix zone and 84°F for the Seattle zone, so the same 1985 house needs 3.5 tons in Phoenix and 1 ton in Seattle.
Can I quote a 1,500 sq ft job from this table?
Use it for the first conversation with the homeowner. In Atlanta, GA the same 1,500 sq ft comes out at 2 tons or 1.5 tons depending on how the house was built, so run the load for the actual house before you order equipment. Room-by-room Manual J and Manual S equipment selection are in the Pro plan. If the job needs a permit, ask the building department whether it requires a load report from ACCA-approved software.
Used on the same job
Size the actual house in chat
Start with the ZIP. Then describe the house you are quoting, including the windows, insulation and where the ducts run, and the assistant runs the same load tools, asks for what is missing and explains the result in terms you can show the homeowner.
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