Defaults reflect this space type. Same engine as the main calculator.
| Cooling load | — |
An attic room doesn't sit under a roof — it sits inside one. Heat soaks through the slope on both sides, knee-walls hide unconditioned cavities, and the ridge can run 60–70°C in summer sun. Our standard +12% top-floor factor is the floor here; poorly insulated conversions run 25–40% above an equivalent mid-floor room.
Every unit of roof insulation pays twice: smaller AC purchase, lower running cost forever. For converted attics that can't be re-insulated, bias toward the larger borderline size — the one space where our usual 'take the smaller unit' advice reverses — and place the indoor head low on a gable wall, since heat stratifies brutally under a sloped ceiling.
A typical attic room / loft conversion (~200 sq ft) needs about 6,667 BTU/hr — a 1.5 ton unit in moderate US conditions, or 2.5 ton in hot Indian conditions (24,699 BTU/hr).
A typical Indian attic room / loft conversion of ~200 sq ft carries roughly 24,699 BTU/hr in hot conditions — a 2.5 ton. Adjust with the calculator above for your exact room and city.
Plan 15–40% above an equivalent mid-floor room depending on roof insulation — the calculator's top-floor factor covers the typical case, and poor insulation should be selected for most conversions.
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Go deeper: Top-floor heat guide · all guides.