Two rooms of identical size can differ by a factor of four in cooling load. A 120 sq ft study carries about 3,800 BTU/hr. A 120 sq ft server room carries nearly 20,000 — because the equipment inside converts essentially all the electricity it draws into heat, and it does so around the clock.
The factors that move the number are occupancy, equipment and appliance heat, glazing, and whether the space sits inside the conditioned envelope. A kitchen adds an appliance allowance. An attic conversion has roof gain on five surfaces instead of one. A garage usually has no insulation at all. A conservatory is mostly glass, which is why it runs at roughly four times a bedroom's rate per square foot.
Each page below applies the factors specific to that space. The loads shown are for the typical area listed — use the calculator on each page for your own dimensions.
| Space | Typical area | Load | Recommended |
|---|---|---|---|
| Bedroom | 140 sq ft | 4,080 BTU/hr | 5,000 BTU window or portable unit |
| Living Room | 250 sq ft | 9,750 BTU/hr | 10,000 BTU window unit or mini-split |
| Kitchen | 120 sq ft | 7,904 BTU/hr | 8,000 BTU window or portable unit |
| Home Office | 120 sq ft | 5,240 BTU/hr | 6,000 BTU window or portable unit |
| Study / Small Room | 90 sq ft | 3,780 BTU/hr | 5,000 BTU window or portable unit |
| Attic Room / Loft Conversion | 200 sq ft | 6,667 BTU/hr | 7,000 BTU window or portable unit |
| Basement | 600 sq ft | 12,380 BTU/hr | 14,000 BTU window unit or mini-split |
| Sunroom | 200 sq ft | 12,857 BTU/hr | 14,000 BTU window unit or mini-split |
| Conservatory | 180 sq ft | 14,732 BTU/hr | 15,000 BTU mini-split |
| Space | Typical area | Load | Recommended |
|---|---|---|---|
| Garage | 440 sq ft | 13,469 BTU/hr | 14,000 BTU window unit or mini-split |
| Garage Gym | 440 sq ft | 14,669 BTU/hr | 15,000 BTU mini-split |
| Mobile / Manufactured Home | 900 sq ft | 32,652 BTU/hr | 3 ton system |
| Space | Typical area | Load | Recommended |
|---|---|---|---|
| Server Room / IT Closet | 120 sq ft | 19,613 BTU/hr | 2 ton system |
| Gym / Fitness Studio | 1,200 sq ft | 49,760 BTU/hr | 5 ton system |
| Classroom / Coaching Centre | 400 sq ft | 29,860 BTU/hr | 2.5 ton system |
| Restaurant Dining Area | 600 sq ft | 33,040 BTU/hr | 3 ton system |
| Retail Shop | 400 sq ft | 16,460 BTU/hr | 18,000 BTU mini-split |
| Salon / Parlour | 300 sq ft | 14,860 BTU/hr | 15,000 BTU mini-split |
If you know the square footage and the space is a conventional room or home, the AC size chart by room size works from area directly. For an existing unit, the model number decoder reads the capacity straight off the data plate.
Because floor area is only one input. Occupancy, appliance and equipment heat, glazing and whether the space sits inside the conditioned envelope all change the load. A 120 sq ft study carries about 3,800 BTU/hr; a 120 sq ft server room carries nearly 20,000.
A typical 140 sq ft bedroom carries about 4,080 BTU/hr, which is a 5,000 BTU window or portable unit in the US, or a 1.5 ton split in hot Indian conditions.
Conservatories and sunrooms, because they are mostly glass, and server rooms, because equipment converts nearly all the power it draws into heat around the clock. Kitchens come next thanks to the appliance allowance.