Is My Contractor's AC Tonnage Right? How to Check a Quote

Ask for the Manual J

Manual J is the ACCA load calculation most building codes reference. It works room by room from your house's insulation, windows, orientation and local design day. A quote that lists tonnage without one is usually the square-foot rule, or a copy of whatever unit was there before. Ask to see it.

Check the size against the load

ACCA Manual S says a cooling unit should not exceed the calculated load by more than 15%. If the Manual J says 26,000 BTU/hr, a 2.5 ton (30,000) unit is the most it supports; 3 tons is over. Central units come in half-ton steps: 1.5 tons, 2 tons, 2.5 tons, 3 tons, 3.5 tons, 4 tons, 5 tons.

What a typical house needs

For a 2,000 sq ft house with average insulation, the climate-based size across 3,206 cities comes out as:

A quote a full ton above your city's figure deserves a question. A tight, well-insulated house can need less still.

Replacing an old unit

The old unit's size is not evidence. Many were sized by the rule, and the house has probably had new windows, insulation or a new roof since. If the old system short-cycled or left rooms clammy, it was likely too big, and the same size again repeats the problem.

Where to go next

See how far apart the answers run: Bullhead City, AZ, Houston, TX, San Francisco, CA.

Window AC and Mini-Split BTU by Room, Adjusted for Climate · What Central AC Costs to Run, State by State