Sizing screen

AC size planning estimator

Turn conditioned floor area into a deliberately broad comparison band, then collect the house facts a real cooling-load calculation needs. This does not select equipment.

This is a cross-check, not a load calculation.

Use it to spot questions worth asking. Do not order equipment from its result.

Conditioned floor area, square feetCount enclosed floor area served by this system—not porches, garages, or unconditioned attic space.Existing system capacity, tons (optional)Usually shown in the model number or installation records. Leave blank if you are unsure.

Which load-calculation facts do you already have?

These answers do not change the estimate. They build your checklist for a professional calculation.

Local outdoor and indoor design conditions House orientation, window area, shading, and glass performance Wall, ceiling, floor, and roof insulation or assembly details Measured or defensible air-leakage assumptions Duct location, insulation, surface area, and leakage Occupants, ventilation, and important internal loads Separate sensible and latent cooling loads

Enter the conditioned area to see the full DOE comparison band and the inputs still needed for real equipment selection.

See the exact math

One nominal ton equals 12,000 Btu/h. The tool divides conditioned area by 1,000 and 800 for the efficient-home example, and by 500 and 400 for the older rule. It makes no other adjustment.

That large gap is the point: floor area alone does not identify the load. Manual J covers component, infiltration, duct, ventilation, moisture, and other loads; Manual S then checks actual equipment performance against the calculated sensible and latent needs.

Method

The area-only screen reproduces the range in a U.S. Department of Energy guide: an older estimate of one ton per 400–500 square feet and an efficient-home example of one ton per 800–1,000 square feet. It does not add hidden adjustment factors. A contractor must calculate the house load with Manual J, then use Manual S and manufacturer performance data to select equipment.

What this cannot tell you

Floor area cannot account for New Orleans humidity, windows, shade, air leakage, insulation, occupants, ventilation, or ducts.
Nominal tons are not the same as sensible and latent capacity at local design conditions.
The broad result is a comparison screen—not a recommendation, bid specification, permit calculation, or replacement size.