BTU Calculator
A BTU figure says how much heating or cooling a room is likely to need. This uses a common rule of thumb based only on floor area. It is a starting point, not a full heat-load calculation.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The rule of thumb is about 20 BTU per hour for each square foot of floor, for an ordinary room with 8-foot ceilings. The same figure is about 63 watts per square metre.
A ton of cooling is 12,000 BTU per hour, so divide the total by 12,000 to get tons. Sunny rooms, many windows, high ceilings and hot climates usually need more than the rule gives.
Worked example
A room of 300 ft² needs about 6,000 BTU/h of cooling, or 0.5 tons.
Questions
Is this the final size?
No. It is a rough starting figure. A professional load calculation takes insulation, windows and climate into account.
What about several rooms?
Add up the rooms you want to cool. Rooms on one system can behave differently, so ask for a whole-house figure if that is your case.
Does this work for heating?
The same rule is often used as a rough guide for heating too. Heaters are rated in their own way, so check the rating on the unit itself.
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