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HVAC Sizing Calculator

Estimate the heating and cooling capacity a home needs before you get equipment quotes.

The house
sq ft

Count only heated and cooled space. Leave out an unconditioned garage, attic or crawlspace.

ft

Use a floor-area-weighted average if some rooms are vaulted.

Find your county on the IECC climate zone map if none of the cities listed are close.

Each person past the first two adds about 600 BTU/h to the cooling load.

Envelope
Window area
Sun exposure

This is a screening estimate built on BTU-per-square-foot factors by climate zone. It tells you whether a quote is in the right neighborhood. It does not tell you what to buy.

Estimated cooling capacity

3.5tons

40,000 BTU/h of cooling and 54,000 BTU/h of heating at design conditions.
Nearest nominal AC sizeEquipment is built in these steps only
3.5 ton
Heating loadOutput the furnace or heat pump must deliver
54,000 BTU/h
Furnace input at 80% AFUENominal 70k input model
67,500 BTU/h
Furnace input at 95% AFUENominal 60k input model
56,842 BTU/h
Cooling load densityRule-of-thumb range is 400–700 sq ft per ton
540 sq ft/ton

Get a Manual J before you buy equipment

Nothing on this page is a load calculation. An ACCA Manual J measures your actual wall and attic R-values, window U-factor and solar heat gain by orientation, infiltration and duct losses, and it routinely lands a half ton to a full ton away from a square-footage estimate. Insist on one — many jurisdictions require it with the permit, and a contractor who sizes by square footage alone is telling you something about the rest of the work.

Oversizing makes cooling worse, not safer

An oversized air conditioner reaches setpoint before it has run long enough to pull moisture out of the air, then shuts off. You get a house that is cold and clammy, short cycling that wears out the compressor, and a higher bill. If a proposal comes in more than about half a ton above this estimate, ask what load calculation produced it.
How each input moves the load
AdjustmentEffectCooling BTU/hHeating BTU/h
Baseline, climate zone 422 / 30 BTU per sq ft39,60054,000
Ceiling height 8.0 ft×1.00 cool, ×1.00 heat39,60054,000
Insulation — average×1.00 cool, ×1.00 heat39,60054,000
Window area — average×1.00 cool, ×1.00 heat39,60054,000
Sun exposure — average×1.00 cool, ×1.00 heat39,60054,000
Air tightness — average×1.00 cool, ×1.00 heat39,60054,000
Occupants — 3 in the house+600 BTU/h cooling, no heating credit40,20054,000
Design load3.5 tons cooling40,00054,000
Sensitivity — the same house one step better or worse
ScenarioCoolingHeating
As entered3.5 tons54,000 BTU/h
Tight and well insulated instead2.5 tons32,500 BTU/h
Leaky and poorly insulated instead4.5 tons84,500 BTU/h
Spread between those two2.0 tons160%

What this assumes

  • This is a load approximation, not an ACCA Manual J calculation.
  • Climate zone factors follow the IECC climate zone map.
  • Assumes an average building with no unusual solar gain, air leakage or zoning requirements.

Important

A proper equipment selection requires an ACCA Manual J load calculation, Manual S equipment selection and Manual D duct design. Use this to sanity-check a quote, not to order equipment. If a contractor sizes a system by square footage alone, that is a warning sign.

Understanding the result

Oversized equipment performs worse

An oversized air conditioner cools the air to setpoint before it has run long enough to remove humidity, then shuts off. The result is a house that is cold and clammy, with short cycling that wears the compressor and raises the bill. Bigger is actively worse in cooling.

The rule of thumb and why it fails

The old rule — roughly 500 to 600 square feet per ton — ignores insulation, window area and orientation, air leakage, ceiling height and climate. A well-sealed new house and a 1950s house of identical size can differ by more than a full ton.

What Manual J adds

A Manual J calculation measures your actual building: wall and attic R-values, window U-factor and solar heat gain coefficient by orientation, infiltration, duct location and internal gains. Reputable contractors run one before quoting a replacement, and many jurisdictions require it with the permit.

Climate zone shifts the number significantly

The same 2,000 square foot house needs 2.5 tons of cooling in Seattle and 4 tons in Phoenix. Heating load in Minneapolis is 2 to 3 times the heating load in Atlanta for the same house. Climate zone is the single largest variable in any load estimate.

Common questions

How many tons of AC do I need for 2,000 square feet?
Typically between 2.5 and 4 tons depending on climate zone, insulation and window area. That spread is exactly why square-footage rules of thumb are unreliable and why a Manual J calculation is worth insisting on.
Should I replace my system with the same size?
Not automatically. The existing system may have been oversized originally, and if you have added insulation or replaced windows, your load is lower now. Have the load calculated rather than matching the old nameplate.
What size AC do I need for 1500 square feet?
A 1,500 square foot home typically needs 2 to 3 tons (24,000 to 36,000 BTU) depending on climate zone, insulation, and windows. In a hot southern climate with average insulation, 2.5 to 3 tons. In a northern climate with good insulation, 2 to 2.5 tons.
How many BTU per square foot for heating?
Heating load ranges from 25 to 60 BTU per square foot depending on climate. A well-insulated home in a mild climate needs 25 to 35 BTU/sq ft. A poorly insulated home in a cold climate needs 50 to 60 BTU/sq ft. A 2,000 square foot home in Chicago may need 80,000 to 100,000 BTU.
What size furnace for 2000 sq ft house?
A 2,000 square foot home typically needs 60,000 to 80,000 BTU furnace capacity depending on climate and insulation. In a cold northern climate with average insulation, 80,000 to 100,000 BTU. In a mild climate with good insulation, 60,000 BTU may suffice.
Is a 3 ton AC too big for my house?
If your calculated cooling load is 2 tons and you install 3 tons, the system short-cycles — cooling the air quickly without removing humidity. A 50% oversize is worse than a 20% undersize in cooling. Have a Manual J calculation done before selecting equipment size.
What is a ton of AC in BTU?
One ton of air conditioning equals 12,000 BTU per hour. A 3-ton unit delivers 36,000 BTU/hr. A 4-ton unit delivers 48,000 BTU/hr. Tonnage refers to the cooling capacity, not the weight of the equipment.
How do I know if my AC is oversized?
Signs of oversizing: the system runs in short 5 to 10 minute cycles, the house feels cold but clammy, rooms near the thermostat cool unevenly, and the unit never runs long enough to dehumidify. An oversized system also wears out compressors faster from frequent starting.
What SEER rating should I look for?
Minimum SEER is 14 in most states and 15 in the South. SEER 16 to 18 is the sweet spot for cost versus efficiency. Each SEER point above 14 saves roughly 7% on cooling costs. A SEER 18 unit costs $500 to $1,000 more than SEER 14 but saves $100 to $200 per year.
How many square feet per ton of AC?
The rule of thumb is 500 to 600 square feet per ton, but it is unreliable. A well-insulated 2,000 square foot home may need only 2.5 tons (800 sq ft/ton). A poorly insulated home with large windows may need 3.5 tons (570 sq ft/ton). Always use a load calculation.
What size heat pump do I need?
A heat pump is sized to the heating load, which is typically larger than the cooling load in northern climates. A 2,000 square foot home in a mixed climate needs a 3-ton (36,000 BTU) heat pump. In cold climates, supplemental heat strips add 10 to 20 kW for temperatures below the heat pump's balance point.

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