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AC size · 1,700 sq ft
What size AC for a 1,700 sq ft house
A 1,700 sq ft house needs anywhere from 1 ton to 4 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. At the low end 1 ton is a load, not a unit you can order. The 400 to 600 sq ft per ton rule gives 2.83 to 4.25 tons for all of them. Check your zone first.
Run your own house in the calculator. It starts with a 1,700 sq ft single-story house in San Francisco, CA, 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 1,700 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 94103 · San Francisco County, CA · IECC zone 3C · elevation 37 ft · design 84°F DB / 65°F WB cooling, 35°F heating
Cooling load
17,888BTU/h
≈ 1.5 ton (nearest 0.5) · SHR 0.97
Heating load
24,785BTU/h
- Furnace input bin 40,000 BTU/h at 80% AFUE
- Heat pump 30,000 BTU/h at 47°F (27,000 at design temp)
Load breakdown by component
| Component | Cooling | Heating |
|---|---|---|
| Transmission (walls, ceiling, floor, glass, doors) | 3,347 | 15,948 |
| Solar through glass | 9,802 | - |
| Infiltration | 396 | 4,706 |
| Internal gains (people, appliances) | 2,490 | - |
| Ducts in unconditioned attic | 1,852 | 4,131 |
- 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 1,700 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 = 1,700 / 1 = 1,700 sq ft; side = 41 ftThe engine models a square single-story footprint with 8 ft ceilings, which gives about 1,319 sq ft of gross wall and 1,700 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 4 tons.- Square feet per ton
sq ft per ton = 1,700 / (Q_cool / 12,000)Computed from the unrounded load. Across this table one ton covers 441 to 2,031 sq ft.
AC size for a 1,700 sq ft house in 14 climate zones
Each row is the same 1,700 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 | 3 tons35,471 BTU/h · 575 sq ft/ton | 1.5 tons17,519 BTU/h · 1,164 sq ft/ton |
| 2A | Houston, TX | 96°F | 3 tons37,901 BTU/h · 538 sq ft/ton | 1.5 tons18,753 BTU/h · 1,088 sq ft/ton |
| 2B | Phoenix, AZ | 110°F | 4 tons46,210 BTU/h · 441 sq ft/ton | 2 tons22,963 BTU/h · 888 sq ft/ton |
| 3A | Atlanta, GA | 95°F | 2 tons25,505 BTU/h · 800 sq ft/ton | 1.5 tons16,714 BTU/h · 1,221 sq ft/ton |
| 3B | Las Vegas, NV | 100°F | 2.5 tons27,319 BTU/h · 747 sq ft/ton | 1.5 tons18,066 BTU/h · 1,129 sq ft/ton |
| 3C | San Francisco, CA | 84°F | 1.5 tons17,888 BTU/h · 1,140 sq ft/ton | 1 ton11,732 BTU/h · 1,739 sq ft/ton |
| 4A | St. Louis, MO | 92°F | 2 tons23,101 BTU/h · 883 sq ft/ton | 1.5 tons15,130 BTU/h · 1,348 sq ft/ton |
| 4B | Albuquerque, NM | 95°F | 2 tons23,197 BTU/h · 879 sq ft/ton | 1.5 tons15,382 BTU/h · 1,326 sq ft/ton |
| 4C | Seattle, WA | 84°F | 1 ton14,989 BTU/h · 1,361 sq ft/ton | 1 ton10,046 BTU/h · 2,031 sq ft/ton |
| 5A | Chicago, IL | 91°F | 2 tons22,452 BTU/h · 909 sq ft/ton | 1 ton14,425 BTU/h · 1,414 sq ft/ton |
| 5B | Denver, CO | 93°F | 2 tons22,033 BTU/h · 926 sq ft/ton | 1 ton14,291 BTU/h · 1,427 sq ft/ton |
| 6A | Minneapolis, MN | 90°F | 1.5 tons20,448 BTU/h · 998 sq ft/ton | 1 ton13,388 BTU/h · 1,524 sq ft/ton |
| 6B | Billings, MT | 92°F | 1.5 tons20,299 BTU/h · 1,005 sq ft/ton | 1 ton13,419 BTU/h · 1,520 sq ft/ton |
| 7 | Duluth, MN | 86°F | 1.5 tons16,770 BTU/h · 1,216 sq ft/ton | 1 ton11,097 BTU/h · 1,838 sq ft/ton |
8 of the 28 sizes above are under 1.5 tons. Those numbers are loads, not equipment sizes, because the ducted lineup this calculator sizes against starts at 18,000 BTU/h.
Only 3 of the 28 engine results land inside the rule-of-thumb range of 2.83 to 4.25 tons, the 1985 house in zones 1A, 2A and 2B.
Phoenix, AZ splits the widest. The 1985 house with attic ducts needs 4 tons and the tight 2015 house with its ducts inside needs 2 tons, 2 tons apart on the same floor area.
Seattle, WA is the one climate where even the 1985 house lands at 1 ton, on a cooling load of 14,989 BTU/h. The smallest ducted system BuildSolver sizes against is 18,000 BTU/h, 1.5 tons, and that load sits under it. Size a mini split to the load, ducted or ductless, or let one system cover this space and the rooms next to it, and put that in the quote before the homeowner asks why the new unit is smaller than the one coming out.
The highlighted San Francisco row is the calculator's starting point. There the 1985 house needs 17,888 BTU/h, or 1.5 tons, and a heating load of 24,785 BTU/h at 35°F. Built tight in 2015 with the ducts inside, the same house needs 1 ton. 1 ton is a load, not a size the ducted lineup carries. That lineup starts at 1.5 tons, 18,000 BTU/h, so the tight build is a mini split job. A 500 sq ft per ton quote would put 3.5 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 1,700 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 1,700 sq ft house
- Quoting 4.5 tons because the house is 1,700 sq ft. The 400 sq ft per ton rule gives 4.25 tons, which a quote rounds to 4.5 tons. The St. Louis, MO row puts the 1985 house at 2 tons and the 2015 house at 1.5 tons.
- Reusing the tonnage from a job in another market. Carry the Phoenix, AZ tonnage to a Seattle, WA job and you have sold 3 tons more equipment than the house asks for.
- 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. Duluth, MN asks the 1985 house for 61,104 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 1,700 sq ft house
At 1,700 sq ft the same floor area shows up as a wide 1970s ranch, as a split level with the family room half a flight down, or as a Cape Cod with dormers and bedrooms under the roof. The table models one story on a slab. A story and a half with bedrooms under the roof is a different load and the page does not model it, so count the levels and look at what is over the bedrooms before you take a row off it.
- If the bedrooms sit under the roof, the single-story row here is the wrong shape for them. Knee walls, ceilings sloped against the sheathing and ducts run through the space behind them sit outside this model, and those rooms run hot whatever the whole-house number says. Price that floor from its own room load.
- On a split level the lowest level is partly below grade and the top level sits under the attic, so the two ends of the house have opposite problems in the same season. One thermostat in the middle of that stack leaves somebody unhappy. Find where the return sits, then talk tonnage.
- In the cold rows on this page the heating load runs past double the cooling load. The furnace picks the blower and the duct sizes, so in July those same ducts carry far less air than they do in January, supply velocity drops and the air dumps cold near the register. Check the cooling CFM against the duct sizes before you quote the condenser.
Questions about AC size for 1,700 sq ft
What size AC do I need for a 1,700 sq ft house?
Climate and construction decide it. In the table on this page the answer runs from 1 ton in Seattle, WA to 4 tons in Phoenix, AZ. Chicago, IL puts the same house at 2 tons as a 1985 build and 1 ton as a 2015 build. On this page any size under 1.5 tons is a load, not a unit you can order. The ducted lineup starts at 18,000 BTU/h, so those houses take a mini split. Enter your ZIP and the house details in the calculator for your own number.
How many BTU does a 1,700 sq ft house need for cooling?
The cooling loads in the table run from 10,046 to 46,210 BTU/h. Per square foot that is 5.9 to 27.2 BTU/h, so no single BTU per square foot number fits a house this size. 8 of the 28 runs on this page round to a size under the 18,000 BTU/h floor of the ducted lineup, where the job goes to a mini split. Run the actual house in the calculator above for its number.
Is a 4.5-ton AC too big for a 1,700 sq ft house?
ACCA Manual S limits a single-speed cooling unit to 115% of the Manual J load. By that limit a 4.5-ton single-speed unit is oversized for every house on this page, including the 1985 house in Phoenix, AZ at 46,210 BTU/h. Going down from 4.5 tons stops at 18,000 BTU/h, 1.5 tons, where the ducted lineup this calculator sizes against ends. Loads under that number belong to a mini split.
What size furnace goes with a 1,700 sq ft house?
The heating loads in the same runs go from 10,843 to 61,104 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. At the warm end one run comes in light enough that the engine asks for electric resistance heat rather than a furnace. The furnace size calculator shows the heating result for a single ZIP.
Why does a 1,700 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 4 tons in Phoenix and 1 ton in Seattle. The residential ducted lineup this page sizes against starts at 1.5 tons, so the Seattle number lands below it. Mini splits are made in smaller sizes, ducted and ductless, so that job goes to one of those.
Can I quote a 1,700 sq ft job from this table?
Use it for the first conversation with the homeowner. San Francisco, CA puts the same 1,700 sq ft at 1.5 tons or 1 ton depending on how the house was built, so run the load for the actual house before you order equipment. The smaller of those two sits under the 18,000 BTU/h bottom of the lineup, so that build is a mini split job. 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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