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AC size · 2,500 sq ft
What size AC for a 2,500 sq ft house
A 2,500 sq ft house needs anywhere from 1 ton to 5.5 tons of cooling in the 14 climates below. The low end is a tight 2015 house in Seattle, WA and the high end is a 1985 house with attic ducts in Phoenix, AZ. The 400 to 600 sq ft per ton rule gives 4.17 to 6.25 tons for all of them, and its top end is past the 5-ton limit of one residential split system. Check your zone first.
Run your own house in the calculator. It starts with a 2,500 sq ft two-story house in Miami, FL, 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 2,500 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 33101 · Miami-Dade County, FL · IECC zone 1A · elevation not determined reliably - altitude correction not applied · design 92°F DB / 79°F WB cooling, 47°F heating
Cooling load
50,124BTU/h
≈ 4 ton (nearest 0.5) · SHR 0.93
Heating load
27,026BTU/h
- Furnace input bin 40,000 BTU/h at 80% AFUE
- Heat pump 30,000 BTU/h at 47°F (30,000 at design temp)
Load breakdown by component
| Component | Cooling | Heating |
|---|---|---|
| Transmission (walls, ceiling, floor, glass, doors) | 13,452 | 17,967 |
| Solar through glass | 24,994 | - |
| Infiltration | 3,758 | 4,554 |
| Internal gains (people, appliances) | 2,920 | - |
| Ducts in unconditioned attic | 5,000 | 4,504 |
- Altitude correction not applied for ZIP 33101: the site elevation could not be determined reliably from the Census and USGS data.
- 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 2,500 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 = 2,500 / 2 = 1,250 sq ft; side = 35 ftThe engine models a square two-story footprint with 8 ft ceilings, which gives about 2,263 sq ft of gross wall and 1,250 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 5.5 tons.- Square feet per ton
sq ft per ton = 2,500 / (Q_cool / 12,000)Computed from the unrounded load. Across this table one ton covers 464 to 2,151 sq ft.
AC size for a 2,500 sq ft house in 14 climate zones
Each row is the same 2,500 sq ft two-story house on a slab with 4 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 | 4 tons50,124 BTU/h · 599 sq ft/ton | 2 tons24,415 BTU/h · 1,229 sq ft/ton |
| 2A | Houston, TX | 96°F | 4.5 tons53,412 BTU/h · 562 sq ft/ton | 2 tons26,087 BTU/h · 1,150 sq ft/ton |
| 2B | Phoenix, AZ | 110°F | 5.5 tons64,628 BTU/h · 464 sq ft/ton | 2.5 tons31,779 BTU/h · 944 sq ft/ton |
| 3A | Atlanta, GA | 95°F | 3 tons36,174 BTU/h · 829 sq ft/ton | 2 tons23,482 BTU/h · 1,278 sq ft/ton |
| 3B | Las Vegas, NV | 100°F | 3 tons38,714 BTU/h · 775 sq ft/ton | 2 tons25,381 BTU/h · 1,182 sq ft/ton |
| 3C | San Francisco, CA | 84°F | 2 tons25,254 BTU/h · 1,188 sq ft/ton | 1.5 tons16,351 BTU/h · 1,835 sq ft/ton |
| 4A | St. Louis, MO | 92°F | 2.5 tons32,620 BTU/h · 920 sq ft/ton | 2 tons21,350 BTU/h · 1,405 sq ft/ton |
| 4B | Albuquerque, NM | 95°F | 2.5 tons32,668 BTU/h · 918 sq ft/ton | 2 tons21,692 BTU/h · 1,383 sq ft/ton |
| 4C | Seattle, WA | 84°F | 1.5 tons20,941 BTU/h · 1,433 sq ft/ton | 1 ton13,948 BTU/h · 2,151 sq ft/ton |
| 5A | Chicago, IL | 91°F | 2.5 tons31,878 BTU/h · 941 sq ft/ton | 1.5 tons20,183 BTU/h · 1,486 sq ft/ton |
| 5B | Denver, CO | 93°F | 2.5 tons31,221 BTU/h · 961 sq ft/ton | 1.5 tons19,950 BTU/h · 1,504 sq ft/ton |
| 6A | Minneapolis, MN | 90°F | 2.5 tons28,873 BTU/h · 1,039 sq ft/ton | 1.5 tons18,695 BTU/h · 1,605 sq ft/ton |
| 6B | Billings, MT | 92°F | 2.5 tons28,602 BTU/h · 1,049 sq ft/ton | 1.5 tons18,706 BTU/h · 1,604 sq ft/ton |
| 7 | Duluth, MN | 86°F | 2 tons23,565 BTU/h · 1,273 sq ft/ton | 1.5 tons15,393 BTU/h · 1,949 sq ft/ton |
Only 2 of the 28 engine results land inside the rule-of-thumb range of 4.17 to 6.25 tons, the 1985 house in zones 2A and 2B.
In Phoenix, AZ the 1985 house with attic ducts needs 5.5 tons and the tight 2015 house with its ducts inside needs 2.5 tons, 3 tons apart on the same floor area.
Phoenix, AZ (64,628 BTU/h) rounds the older house to 5.5 tons, a size no residential split comes in. DOE's residential rules cover units rated under 65,000 BTU/h, so pull a 5-ton unit's capacity at the design temperature from the manufacturer's expanded performance data, and plan on two systems only if it falls short of the load.
The highlighted Miami row is the calculator's starting point. There the 1985 house needs 50,124 BTU/h, or 4 tons, and a heating load of 27,026 BTU/h at 47°F. Built tight in 2015 with the ducts inside, the same house needs 2 tons. A 500 sq ft per ton quote would put 5 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 2,500 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 3 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.
- The engine treats both stories as one zone. The page cannot split the load between floors, and a bonus room over a garage is not modeled.
- 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 2,500 sq ft house
- Quoting 5 tons because the house is 2,500 sq ft. The 400 sq ft per ton rule gives 6.25 tons, past the largest residential split system, so the quote lands on 5 tons. In the St. Louis, MO row the engine puts the 1985 house at 2.5 tons and the 2015 house at 2 tons.
- Reusing the tonnage from a job in another market. The same 1985 house with attic ducts needs 1.5 tons in Seattle, WA and 5.5 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 75,771 BTU/h of heat and 2 tons of cooling. Pick the furnace and the AC from their own loads.
What to check on a 2,500 sq ft house
At 2,500 sq ft you are usually looking at a two-story house with a bonus room over the garage, a finished attic room or a primary suite downstairs. Houses this size often run two systems already, one per floor. Ask before you quote one.
- A bonus room over the garage has three exposed surfaces and usually the longest duct run in the house. It is usually the first room the homeowner calls about. Check its supply run and the insulation around it before you touch the equipment size.
- If the house has two systems, divide the load by floor before you size either replacement. Replacing both at the old tonnage repeats the original oversizing twice.
- DOE's residential central air conditioner rules cover units under 65,000 BTU/h, so 5 tons nominal is the top of the residential split range and past that the job needs two systems or light commercial equipment. Check the table for your zone before you price one large system, because an older house this size in a desert zone comes close to that line.
Questions about AC size for 2,500 sq ft
What size AC do I need for a 2,500 sq ft house?
Climate and construction decide it. In the table on this page the answer runs from 1 ton in Seattle, WA to 5.5 tons in Phoenix, AZ. In Chicago, IL the same house comes out at 2.5 tons as a 1985 build and 1.5 tons as a 2015 build. Enter your ZIP and the house details in the calculator for your own number.
How many BTU does a 2,500 sq ft house need for cooling?
The cooling loads in the table run from 13,948 to 64,628 BTU/h. Per square foot that is 5.6 to 25.9 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 5-ton AC too big for a 2,500 sq ft house?
The 400 sq ft per ton rule gives 6.25 tons here, past the 5-ton top of residential split systems, so the largest unit a rule-of-thumb quote can land on is 5 tons. ACCA Manual S limits a single-speed cooling unit to 115% of the Manual J load. By that limit a 5-ton single-speed unit is oversized for the 1985 house in 12 of the 14 climates and for the 2015 house in 14 of them.
What size furnace goes with a 2,500 sq ft house?
The heating loads in the same runs go from 13,092 to 75,771 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 100,000 BTU/h bin. The furnace size calculator shows the heating result for a single ZIP.
Why does a 2,500 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 5.5 tons in Phoenix and 1.5 tons in Seattle.
Can I quote a 2,500 sq ft job from this table?
Use it for the first conversation with the homeowner. In Miami, FL the same 2,500 sq ft comes out at 4 tons or 2 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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