What is BTU

The British thermal unit (BTU or Btu) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. In science, the joule, the SI unit of energy, has largely replaced the BTU.

The BTU is most often used as a measure of power (as BTU/h or BTUH) in the power, steam generation, heating, and air conditioning industries, and also as a measure of agricultural energy production (BTU/kg). It is still used in metric English-speaking countries, and remains the standard unit of classification for air conditioning units manufactured and sold in many non-English-speaking metric countries. – Wikipedia

How do you calculate the BTU size?

Here follows as a guide only.  For a precise heat load calculation, contact Crystal Air. For offices, homes and your average area requiring air conditioning always keep the following factors in mind:

Size of the area (m)

If the height of the ceiling is over 3m, then add on the increased percentage of the area, or use the Heat Load Calculation Sheet.

Exposure to direct sunlight

Is there excessive heat gain from large or many windows or a non-insulated roof etc?

Curtains and blinds

Eg – If the area is an office with blinds or glazed windows, the heat gain is reduced.

Type of building construction

A brick construction will generally be cooler than a timber or metal one!

Number of people in the area and level of activity

An office with two people can be considered a ‘standard’ heat load.  However, an office of the same size with eight people is not.  A person seated at an office desk gives off less heat than someone who is more active e.g. in a reception area or a restaurant eating and drinking.

Extraction and intake of air

If air is added to an area (eg via an open window), this air will be warmer than the air in the given area and will need to pass through the refrigeration cycle to lower its temperature, causing the air conditioner to work ‘harder’.  Thus the capacity is affected.

Electrical equipment in use

An empty office in a building with no people in it might not generate much of a heat load but, in a computer room, the heat generated by the equipment will increase the heat load, affecting the capacity.  An excessive number of lights will have a similar effect.  Should the area being calculated be considered a ‘standard’ heat load, then the following average heat load calculation could be used:

20m² × 600 = 12000btu air con needed for area

How to calculate aircon size

The basic rule of thumb is to measure the length and breadth of the room and determine the area, then to times that with 600btu per square meter.

Eg: 5m × 4m = 20m²
20m² × 600 = 12000btu air con needed for area