Maintained by the BuildSolver engineering team · Updated
AC size · 3,000 sq ft
What size AC for a 3,000 sq ft house
A 3,000 sq ft house needs anywhere from 1.5 tons to 6.5 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 5 to 7.5 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 3,000 sq ft two-story house in Las Vegas, NV, 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 3,000 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 89101 · Clark County, NV · IECC zone 3B · elevation 1,877 ft · design 100°F DB / 67°F WB cooling, 25°F heating
Cooling load
45,579BTU/h
≈ 4 ton (nearest 0.5) · SHR 0.98
Heating load
45,583BTU/h
- Furnace input bin 60,000 BTU/h at 80% AFUE
- Heat pump 60,000 BTU/h at 47°F (48,000 at design temp)
Load breakdown by component
| Component | Cooling | Heating |
|---|---|---|
| Transmission (walls, ceiling, floor, glass, doors) | 15,096 | 27,999 |
| Solar through glass | 20,541 | - |
| Infiltration | 1,816 | 9,986 |
| Internal gains (people, appliances) | 3,350 | - |
| Ducts in unconditioned attic | 4,776 | 7,597 |
- 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 3,000 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 = 3,000 / 2 = 1,500 sq ft; side = 39 ftThe engine models a square two-story footprint with 8 ft ceilings, which gives about 2,479 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 1.5 tons and 6.5 tons.- Square feet per ton
sq ft per ton = 3,000 / (Q_cool / 12,000)Computed from the unrounded load. Across this table one ton covers 472 to 2,197 sq ft.
AC size for a 3,000 sq ft house in 14 climate zones
Each row is the same 3,000 sq ft two-story house on a slab with 5 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 | 5 tons59,456 BTU/h · 605 sq ft/ton | 2.5 tons28,746 BTU/h · 1,252 sq ft/ton |
| 2A | Houston, TX | 96°F | 5.5 tons63,280 BTU/h · 569 sq ft/ton | 2.5 tons30,658 BTU/h · 1,174 sq ft/ton |
| 2B | Phoenix, AZ | 110°F | 6.5 tons76,314 BTU/h · 472 sq ft/ton | 3 tons37,161 BTU/h · 969 sq ft/ton |
| 3A | Atlanta, GA | 95°F | 3.5 tons42,672 BTU/h · 844 sq ft/ton | 2.5 tons27,591 BTU/h · 1,305 sq ft/ton |
| 3B | Las Vegas, NV | 100°F | 4 tons45,579 BTU/h · 790 sq ft/ton | 2.5 tons29,762 BTU/h · 1,210 sq ft/ton |
| 3C | San Francisco, CA | 84°F | 2.5 tons29,875 BTU/h · 1,205 sq ft/ton | 1.5 tons19,272 BTU/h · 1,868 sq ft/ton |
| 4A | St. Louis, MO | 92°F | 3 tons38,555 BTU/h · 934 sq ft/ton | 2 tons25,097 BTU/h · 1,434 sq ft/ton |
| 4B | Albuquerque, NM | 95°F | 3 tons38,539 BTU/h · 934 sq ft/ton | 2 tons25,443 BTU/h · 1,415 sq ft/ton |
| 4C | Seattle, WA | 84°F | 2 tons24,734 BTU/h · 1,455 sq ft/ton | 1.5 tons16,389 BTU/h · 2,197 sq ft/ton |
| 5A | Chicago, IL | 91°F | 3 tons37,688 BTU/h · 955 sq ft/ton | 2 tons23,812 BTU/h · 1,512 sq ft/ton |
| 5B | Denver, CO | 93°F | 3 tons36,852 BTU/h · 977 sq ft/ton | 2 tons23,502 BTU/h · 1,532 sq ft/ton |
| 6A | Minneapolis, MN | 90°F | 3 tons34,214 BTU/h · 1,052 sq ft/ton | 2 tons22,069 BTU/h · 1,631 sq ft/ton |
| 6B | Billings, MT | 92°F | 3 tons33,855 BTU/h · 1,063 sq ft/ton | 2 tons22,054 BTU/h · 1,632 sq ft/ton |
| 7 | Duluth, MN | 86°F | 2.5 tons27,913 BTU/h · 1,290 sq ft/ton | 1.5 tons18,163 BTU/h · 1,982 sq ft/ton |
Only 3 of the 28 engine results land inside the rule-of-thumb range of 5 to 7.5 tons, the 1985 house in zones 1A, 2A and 2B.
In Phoenix, AZ the 1985 house with attic ducts needs 6.5 tons and the tight 2015 house with its ducts inside needs 3 tons, 3.5 tons apart on the same floor area.
Phoenix, AZ (76,314 BTU/h) puts the older house's cooling load at 65,000 BTU/h or more. DOE's residential central air conditioner rules cover units rated under 65,000 BTU/h, so plan on two systems for that house.
Houston, TX (63,280 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 Las Vegas row is the calculator's starting point. There the 1985 house needs 45,579 BTU/h, or 4 tons, and a heating load of 45,583 BTU/h at 25°F. Built tight in 2015 with the ducts inside, the same house needs 2.5 tons. A 500 sq ft per ton quote would come to 6 tons for both, past the largest residential split system. 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 3,000 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 3.5 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 3,000 sq ft house
- Quoting 5 tons because the house is 3,000 sq ft. The 400 sq ft per ton rule gives 7.5 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 3 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 2 tons in Seattle, WA and 6.5 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 87,504 BTU/h of heat and 2.5 tons of cooling. Pick the furnace and the AC from their own loads.
What to check on a 3,000 sq ft house
A 3,000 sq ft house is a large two-story or a single story with a finished walkout basement, typically four or five bedrooms. At this size the design question is how many systems and zones the house needs, and where each zone boundary falls.
- Residential split systems stop at 5 tons nominal, the top of DOE's residential range of under 65,000 BTU/h. Where a cooling load in the table reaches 65,000 BTU/h, it has to be split between two systems. A load from 63,000 to 64,999 BTU/h shows as 5.5 tons in the table but is still under that line, so compare it with the capacity of the 5-ton unit you would install before splitting the system.
- A finished basement below grade adds little cooling load and a real heating load. Size the basement zone from its own load calculation.
- In mild zones a large house often comes in 2 tons or more under the rule-of-thumb number, as the San Francisco and Seattle rows show. That gap is worth showing the homeowner before quoting two 3-ton systems.
Questions about AC size for 3,000 sq ft
What size AC do I need for a 3,000 sq ft house?
Climate and construction decide it. In the table on this page the answer runs from 1.5 tons in San Francisco, CA to 6.5 tons in Phoenix, AZ. In Chicago, IL the same house comes out at 3 tons as a 1985 build and 2 tons as a 2015 build. Enter your ZIP and the house details in the calculator for your own number.
How many BTU does a 3,000 sq ft house need for cooling?
The cooling loads in the table run from 16,389 to 76,314 BTU/h. Per square foot that is 5.5 to 25.4 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 3,000 sq ft house?
The 400 sq ft per ton rule gives 7.5 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 11 of the 14 climates and for the 2015 house in 14 of them.
What size furnace goes with a 3,000 sq ft house?
The heating loads in the same runs go from 14,892 to 87,504 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 120,000 BTU/h bin. The furnace size calculator shows the heating result for a single ZIP.
Why does a 3,000 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 6.5 tons in Phoenix and 2 tons in Seattle.
Can I quote a 3,000 sq ft job from this table?
Use it for the first conversation with the homeowner. In Las Vegas, NV the same 3,000 sq ft comes out at 4 tons or 2.5 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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