Maintained by the BuildSolver engineering team · Updated
AC size · 1,000 sq ft
What size AC for a 1,000 sq ft house
A 1,000 sq ft house needs anywhere from 0.5 tons to 2.5 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 1.67 to 2.5 tons for all of them. Check your zone first.
Run your own house in the calculator. It starts with a 1,000 sq ft single-story house in Houston, TX, 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 1,000 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 77002 · Harris County, TX · IECC zone 2A · elevation 43 ft · design 96°F DB / 78°F WB cooling, 25°F heating
Cooling load
23,650BTU/h
≈ 2 ton (nearest 0.5) · SHR 0.95
Heating load
27,266BTU/h
- Furnace input bin 40,000 BTU/h at 80% AFUE
- Heat pump 36,000 BTU/h at 47°F (28,800 at design temp)
Load breakdown by component
| Component | Cooling | Heating |
|---|---|---|
| Transmission (walls, ceiling, floor, glass, doors) | 7,804 | 19,163 |
| Solar through glass | 9,998 | - |
| Infiltration | 1,388 | 3,558 |
| Internal gains (people, appliances) | 2,060 | - |
| Ducts in unconditioned attic | 2,401 | 4,544 |
- 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 1,000 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 = 1,000 / 1 = 1,000 sq ft; side = 32 ftThe engine models a square single-story footprint with 8 ft ceilings, which gives about 1,012 sq ft of gross wall and 1,000 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 0.5 tons and 2.5 tons.- Square feet per ton
sq ft per ton = 1,000 / (Q_cool / 12,000)Computed from the unrounded load. Across this table one ton covers 414 to 1,785 sq ft.
AC size for a 1,000 sq ft house in 14 climate zones
Each row is the same 1,000 sq ft single-story house on a slab with 2 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 tons22,088 BTU/h · 543 sq ft/ton | 1 ton11,343 BTU/h · 1,058 sq ft/ton |
| 2A | Houston, TX | 96°F | 2 tons23,650 BTU/h · 507 sq ft/ton | 1 ton12,172 BTU/h · 986 sq ft/ton |
| 2B | Phoenix, AZ | 110°F | 2.5 tons29,000 BTU/h · 414 sq ft/ton | 1.5 tons15,013 BTU/h · 799 sq ft/ton |
| 3A | Atlanta, GA | 95°F | 1.5 tons16,281 BTU/h · 737 sq ft/ton | 1 ton10,913 BTU/h · 1,100 sq ft/ton |
| 3B | Las Vegas, NV | 100°F | 1.5 tons17,502 BTU/h · 686 sq ft/ton | 1 ton11,830 BTU/h · 1,014 sq ft/ton |
| 3C | San Francisco, CA | 84°F | 1 ton11,461 BTU/h · 1,047 sq ft/ton | 0.5 tons7,715 BTU/h · 1,555 sq ft/ton |
| 4A | St. Louis, MO | 92°F | 1 ton14,713 BTU/h · 816 sq ft/ton | 1 ton9,908 BTU/h · 1,211 sq ft/ton |
| 4B | Albuquerque, NM | 95°F | 1 ton14,851 BTU/h · 808 sq ft/ton | 1 ton10,129 BTU/h · 1,185 sq ft/ton |
| 4C | Seattle, WA | 84°F | 1 ton9,723 BTU/h · 1,234 sq ft/ton | 0.5 tons6,724 BTU/h · 1,785 sq ft/ton |
| 5A | Chicago, IL | 91°F | 1 ton14,304 BTU/h · 839 sq ft/ton | 1 ton9,380 BTU/h · 1,279 sq ft/ton |
| 5B | Denver, CO | 93°F | 1 ton14,111 BTU/h · 850 sq ft/ton | 1 ton9,339 BTU/h · 1,285 sq ft/ton |
| 6A | Minneapolis, MN | 90°F | 1 ton12,994 BTU/h · 924 sq ft/ton | 0.5 tons8,726 BTU/h · 1,375 sq ft/ton |
| 6B | Billings, MT | 92°F | 1 ton12,947 BTU/h · 927 sq ft/ton | 0.5 tons8,778 BTU/h · 1,367 sq ft/ton |
| 7 | Duluth, MN | 86°F | 1 ton10,749 BTU/h · 1,116 sq ft/ton | 0.5 tons7,310 BTU/h · 1,642 sq ft/ton |
Only 3 of the 28 engine results land inside the rule-of-thumb range of 1.67 to 2.5 tons, the 1985 house in zones 1A, 2A and 2B.
In Miami, FL the 1985 house with attic ducts needs 2 tons and the tight 2015 house with its ducts inside needs 1 ton, 1 ton apart on the same floor area.
In 9 of the 14 climates, zones 3C, 4A, 4B, 4C, 5A, 5B, 6A, 6B and 7, even the older house rounds to 1 ton or less, on cooling loads from 9,723 to 14,851 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 Houston row is the calculator's starting point. There the 1985 house needs 23,650 BTU/h, or 2 tons, and a heating load of 27,266 BTU/h at 25°F. Built tight in 2015 with the ducts inside, the same house needs 1 ton. A 500 sq ft per ton quote would put 2 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 1,000 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 Miami, FL already land 1 ton 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 1,000 sq ft house
- Quoting 2.5 tons because the house is 1,000 sq ft. That is the top of the 400 sq ft per ton rule. In the St. Louis, MO row the engine puts the 1985 house at 1 ton 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 San Francisco, CA and 2.5 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 41,371 BTU/h of heat and 1 ton of cooling. Pick the furnace and the AC from their own loads.
What to check on a 1,000 sq ft house
A 1,000 sq ft house is usually a two-bedroom ranch, a starter home from the 1950s to the 1970s, or a newer cottage or ADU. Many of these homes never had ducts. They ran on window units or a wall furnace, so the first question on the walkthrough is where the air handler and the returns will go. Start there.
- On a small house the load often falls below the smallest ducted equipment. A tight 1,000 sq ft house in a mild zone can need less than one ton, so price a ductless mini split or a variable-speed unit with a low minimum capacity for those jobs.
- Check the windows next. On a house this small the glass is a large share of the wall. Run the calculator with single pane and then with low-e glass to see how far the window type moves this house.
- Ducts in a vented attic add a bigger share of the load on a small house. If the ducts can go inside, the load and the equipment both drop.
Questions about AC size for 1,000 sq ft
What size AC do I need for a 1,000 sq ft house?
Climate and construction decide it. In the table on this page the answer runs from 0.5 tons in San Francisco, CA to 2.5 tons in Phoenix, AZ. In Chicago, IL the same house comes out at 1 ton 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 1,000 sq ft house need for cooling?
The cooling loads in the table run from 6,724 to 29,000 BTU/h. Per square foot that is 6.7 to 29 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 2.5-ton AC too big for a 1,000 sq ft house?
ACCA Manual S limits a single-speed cooling unit to 115% of the Manual J load. By that limit a 2.5-ton single-speed unit is oversized for the 1985 house in 13 of the 14 climates and for the 2015 house in 14 of them.
What size furnace goes with a 1,000 sq ft house?
The heating loads in the same runs go from 7,596 to 41,371 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 60,000 BTU/h bin. The furnace size calculator shows the heating result for a single ZIP.
Why does a 1,000 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 2.5 tons in Phoenix and 1 ton in Seattle.
Can I quote a 1,000 sq ft job from this table?
Use it for the first conversation with the homeowner. In Houston, TX the same 1,000 sq ft comes out at 2 tons or 1 ton 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.
Open the chat