Defaults reflect this space type, including its typical equipment/metabolic load of ~500 BTU/hr. Same engine as the main calculator.
| Cooling load | — |
Below-grade walls sit against ~13°C earth — a basement's sensible cooling load is a fraction of the same area upstairs (the calculation below uses shaded exposure and no solar windows for this reason). Contractors who size basements by square footage routinely install double the needed capacity, producing the clammiest rooms in the house.
Basements need moisture removal more than temperature drop. An oversized unit satisfies the thermostat in minutes and leaves the damp — the musty-basement smell is the result. Right answer: the smallest unit that covers the calculated load, run long and low; in many basements a dehumidifier plus modest cooling beats a big AC outright.
A typical basement (~600 sq ft) needs about 12,380 BTU/hr — a 1.5 ton unit in moderate US conditions; hot climates run 15–25% higher.
Plan on roughly 12,380 BTU/hr for a typical ~600 sq ft basement in a moderate climate, with the space-specific factors described on this page already included. Hot climates (Zone 1–2) add 15–25%.
Almost always oversizing: the unit cools the air quickly and shuts off before condensing moisture. A smaller unit running longer cycles — or a dedicated dehumidifier — fixes what more tonnage cannot.
Garage Garage Gym Bedroom Living Room Kitchen Sunroom Attic Room / Loft Conversion Home Office Server Room / IT Closet Retail Shop Restaurant Dining Area Salon / Parlour Gym / Fitness Studio Classroom / Coaching Centre Mobile / Manufactured Home Conservatory Study / Small Room
Go deeper: Humidity guide · all guides.