BTU for Room Cooling Calculator
BTU/hr needed = ft² × climate factor (20-30 BTU/ft² for typical US climates).
Result
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How to use this calculator
- Enter room area.
- Pick climate / sun exposure.
- Add extra occupants beyond 2.
About this calculator
Room AC sizing follows the rule of thumb: 20-30 BTU per ft², adjusted for sun exposure, insulation, and occupants. Window units are typically 5-25k BTU/hr; central AC is sized in tons (1 ton = 12,000 BTU/hr). Oversizing causes short-cycling and poor humidity control; under-sizing means the unit runs constantly.
Frequently asked
How does climate affect this?+
Hotter / sunnier rooms need more cooling per ft². A south-facing room with big windows: 30+ BTU/ft². A shaded interior: 20 BTU/ft².
What if the room is under a hot attic?+
Add 10% to the BTU. Top floors need more cooling than ground floors.
Window AC vs central?+
Window: per-room sizing, simple. Central: whole-house Manual J calculation, ducts matter.
Why not just oversize?+
Oversize ACs cycle on/off too fast — can't remove humidity. Result: cold but clammy.
Climate zone matters?+
For window units, just sun exposure. For central AC, full Manual J — climate zone, infiltration, duct losses.
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