Before buying an air conditioner, one question always comes up: how do you calculate the right BTU rating, and what does it actually mean? The BTU figure tells you how much energy the unit needs to cool or heat a space effectively. Getting it right matters just as much as picking the correct energy class.
BTU for air conditioners: what is it?
BTU stands for British Thermal Unit. It measures the amount of energy required to raise the temperature of 1 pound of water (roughly 450 g) by 1 degree Fahrenheit. In the context of air conditioners, it tells you how much heat the unit can remove from the air in a room per hour. The higher the BTU rating, the more powerful the unit.
How many BTU do you need for your air conditioner?
An undersized unit will struggle to reach the target temperature and waste energy running continuously. An oversized one will short-cycle, regulate humidity poorly, and still cost more to run than necessary.
To find the right BTU rating, you need to factor in:
- the size of the room;
- how much direct sunlight the room and building receive;
- the quality of insulation in walls and ceiling;
- the quality of windows and doors;
- how many hours per day the room is occupied;
- the number of people in the household;
- the typical outdoor temperatures in your area.
BTU calculation: how many watts is one BTU?
In Europe, electricity consumption is usually quoted in kWh. The conversion factor is:
1 kilowatt-hour = 3,412.14 BTU/h
To convert BTU to kWh, divide the BTU figure by 3,412.14.
Example: an air conditioner rated at 9,000 BTU/h works out to:
9,000 BTU/h ÷ 3,412.14 = 2.63 kWh
So a 9,000 BTU unit consumes around 2.63 kW per hour of operation.
How many BTU per square metre do you need?
The BTU rating always has to be read in relation to the room's floor area.
Example: a living room of around 20 m² with 3-metre ceilings, average sun exposure, average insulation, and 3 occupants will need an air conditioner rated at least 8,000 BTU.
As the room size increases, you need progressively more powerful units. The variables above, particularly sun exposure and insulation quality, can shift the figure noticeably in either direction.
Browse our air conditioner range in our online store to find the right unit for your space.