BTU calculator
Enter the room size, how sunny it is and how many people use it. You get the BTU per hour to cool it by the ENERGY STAR chart and the air conditioner size to buy, or switch to heating for the BTU to heat it in your climate.
Inputs
Result
BTU chart by room size
ENERGY STAR’s room air conditioner sizing: cooling capacity for an average room with two people, and what it works out to per square foot.
| Room area, ft² | BTU/h | BTU per ft² | Watts of cooling |
|---|
How it is worked out
A 15 x 20 ft room is 300 ft²: 7,000 BTU/h by the ENERGY STAR chart. If it is very sunny, 7,700, so an 8,000 BTU/h air conditioner. Add two more people and it is 8,900: a 9,000. As a kitchen, 11,000 to 11,700: a 12,000.
BTU per square foot
Cooling works out to about 33 BTU/h per square foot for a small 150 ft² room, about 22 at 500 ft² and 14 at 2,500 ft², because a large room has less wall and window for its floor area. The "20 BTU per square foot" rule of thumb is close only for mid-sized rooms. For heating, the rule of thumb runs from 30 BTU/h per square foot in the warmest US climate zone to 60 in the coldest.
Bigger is not better
An oversized air conditioner cools the room quickly and shuts off before it has pulled the moisture out, leaving it cold and clammy; it also cycles more and costs more. ENERGY STAR's chart is meant to be followed, then adjusted for sun, people and kitchens.
For a ductless system room by room, use the mini split size calculator; for a whole house, the AC tonnage calculator and the furnace size calculator.
Questions
How many BTU do I need to cool a room?
Use the ENERGY STAR chart: 5,000 BTU/h for 100 to 150 ft², 7,000 for 250 to 300, 10,000 for 400 to 450, 12,000 for 450 to 550 and 18,000 for 700 to 1,000. Add 10% for a very sunny room, 600 per extra person and 4,000 for a kitchen.
What size AC for a 500 square foot room?
12,000 BTU/h by the ENERGY STAR chart for an average room; about 13,200 if it is very sunny, so the next size up.
How many BTU per square foot?
For cooling, about 20 to 33 BTU/h per ft² for typical rooms by the ENERGY STAR chart, less for very large rooms. For heating, 30 to 60 BTU/h per ft² depending on climate zone.
How many BTU to cool 1,000 square feet?
18,000 BTU/h for one open space by the ENERGY STAR chart, 1.5 tons.
How many watts is 10,000 BTU?
10,000 BTU/h of cooling or heat is 2,931 W, or 2.93 kW: divide BTU/h by 3.412. That is the heat moved, not the electricity used; an air conditioner draws a fraction of it.
How many BTU is 1 ton?
12,000 BTU/h. A 24,000 BTU/h unit is 2 tons.
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