Formula and input notes
Screening cooling load (BTU/h) = conditioned area × load factor × adjustment factor; nominal tons = BTU/h ÷ 12,000
| Input | Practical note |
|---|---|
| Conditioned area | Use the floor area served by the proposed system, excluding unconditioned zones; area alone does not describe the building load. |
| Load factor | This user-supplied BTU/h-per-square-foot factor controls the screening load directly. It is not derived from the envelope or weather by this tool. |
| Ceiling/climate factor | Use this multiplier only for an adjustment you can justify; it combines effects that a full load calculation would model separately. |
Worked ac tonnage example
AC Tonnage Calculator example: 398 ft² × 25 BTU/h·ft² × 1.1 = 10,945 BTU/h. Dividing by 12,000 gives 0.91 nominal cooling tons.
Interpret BTU/h and nominal cooling tons
Use the tonnage only to frame an early conversation; final equipment should be selected from a room-by-room load calculation and manufacturer performance data.
What a proper cooling-load calculation adds
Climate, orientation, windows, air leakage, insulation, ducts, occupants, internal gains, ceiling height, humidity, and ventilation are not captured by one factor.
Questions specific to this calculation
How many BTU per hour are in one nominal ton of cooling?
The calculator uses 12,000 BTU/h per nominal ton. It divides the screening BTU/h result by 12,000; that conversion does not by itself select equipment.
Why is square footage not enough for final AC sizing?
A proper load calculation considers weather design conditions, envelope assemblies, windows, orientation, infiltration, ventilation, ducts, internal gains, and zoning. The entered area factor and multiplier do not model those components.
Before selecting nominal cooling tons, compare this area-factor screen with a residential cooling-load calculation performed under ANSI/ACCA Manual J; this page does not implement that procedure.