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.