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Short guide for planning and estimating air conditioning.

BTU: British thermal unit. The quantity of energy required to raise the temperature of one pound of water by one degree Fahrenheit.

The higher the BTU output, the more powerful the heating or cooling system.

When shopping for heating or cooling systems, the BTU numbers should primarily be used as a comparison between systems. Larger and more expensive systems should provide significantly higher BTUs than smaller ones.




The following guide is based on a room with normal insulation and two person occupancy.


Area to Be Cooled
in Square Feet
Approximate Cooling
btu/h Required
100-150 5,000
150-250 6,000
250-300 7,000
300-350 8,000
350-400 9,000
400-450 10,000
450-550 12,000
550-700 14,000
700-1000 18,000
1000-1200 21,000
1200-1400 23,000
1400-1500 24,000
1500-2000 30,000
2000-2500 34,000


Example: 20’ x 30’ office = 600 square feet

5 people will occupy the office

Using the chart, 14,000 but/h are recommended + 500 btu/h for each person over two (3 x 500 = 1,500 btu/h.)

Total needed for 600 square foot office with 5 people:

14,000 + 1,500 = 15,500 btu/h

Note! It is better to supply two units half the size located at either end of the building to provide more even distribution.


The chart is provided for ESTIMATING PURPOSES only.
Requirements vary based on part of the country, heating/cooling loads, etc...
If a more accurate figure is required, please ask a qualified engineer.


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