AC Cooling Load Calculator (BTU) — Free Manual J Lite
How many BTUs do I need for my room size?
A quick starting point is 20–25 BTU/hr per square foot of conditioned space, so a 400 sq ft room lands around 8,000–10,000 BTU/hr. Sun exposure, ceiling height, insulation, and the number of occupants all shift that up or down. Enter your room details into the calculator for a Manual J-style estimate — an oversized unit short-cycles and will not dehumidify.
Run the numbers for your project
Use the AC Cooling Load Calculator (BTU) — Free Manual J Lite to get an exact answer for your inputs.
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