Cooling BTU Estimate: A Screening Guide

Area starts the estimate; ceiling, sun, and occupants adjust it.

The tool begins with 20 BTU per square foot, scales for ceiling height relative to eight feet, adjusts the envelope load for shade or strong sun, and adds 600 BTU for each occupant above two. It displays a ±10% range to show uncertainty.

Windows, insulation, leakage, climate, ducts, and internal gains matter.

Two rooms with the same floor area can have very different loads. Central systems also depend on duct condition, ventilation, latent moisture load, and room-by-room distribution.

Oversizing can shorten cycles and weaken moisture removal.

DOE guidance notes that oversized room air conditioners can use more energy and remove humidity poorly because of excessive on-off cycling. Choose within manufacturer sizing guidance and avoid rounding far upward “just in case.”

A licensed designer should verify a permanent system.

Use this tool to frame questions and compare room units. For central equipment replacement or major alterations, request a documented Manual J load calculation and confirm local permit and code requirements.

An original illustrative comparison, not a measured household result.

Illustrative room: 12 feet by 15 feet gives 180 square feet. Enter the dimensions and actual conditions in the cooling tool rather than treating the number as an equipment specification. Cooling output in BTU per hour is not the same quantity as electrical input in watts. Neither number alone tells you the cost for a month.

Use the evidence to set the next step.

No. A room screening tool does not model the full building envelope, distribution system, climate, or installation. Use the estimate to frame questions about a room unit; whole-home selection requires an appropriate load assessment.