Air conditioning system capacity is measured in BTUs per hour. It’s sometimes measured in tons, with one ton equaling 12,000 BTUs per hour. An experienced contractor should be hired to calculate the correct size. Square footage plays a part, but factors like insulation, windows, and climate need to be considered too.

Significant advances in energy efficiency have been made with air conditioning technology in recent years. Replacing a unit that is 10 years old or older with a current model can save anywhere from 20 to 40 percent on energy costs. All air conditioning systems are given a BEE rating, BEE stands for Bureau of Energy Efficiency. It ranges from 1 to 5, with higher numbers reflecting superior energy efficiency. Systems with higher BEE ratings cost more, but the extra upfront cost is mitigated by the energy savings going forward.

**Cooling Capacity**

Cooling capacity for a room is defined as the heat load in a room that have to be removed in order to achieve a certain room temperature and humidity. The typical design is set to 24°C temperature and 55% Relative Humidity. Study shows that this combination of temperature and RH is the most conducive for the human body. The unit used to measure heat load is BTU/hr. 1 BTU/hr is the heat energy needed to increase 1 pound of water by 1°F. When choosing an air conditioner, usually a 1 HP (horse power) equipment is able to remove 9,000 BTU/hr of heat. With better technology, some machines are able to remove 10,000 BTU/hr of heat with the same capacity. The higher the listed BTU/hr, the greater the cooling capacity.

**Air Conditioning – Rule Of Thumb**

Calculating the cooling capacity needed for your room is a complicated process as there are many factors to consider. However, there is a simple rule of thumb that you can use to estimate the required cooling capacity for your room. Use this result to compare with the calculation done by the air conditioning contractors for your own checking purposes.

- Find the volume of your room in cubic feet. This is done by measuring the length, width and height of the room in feet and multiply all the three dimensions together as Volume = Width X Length X Height (cubic feet)
- Multiply this volume by 6 as C1 = Volume X 6
- Estimate the number of people (N) that will usually occupy this room. Each person produces about 500 BTU/hr of heat for normal office-related activity. Multiply this two figures together as C2 = N x 500 BTU/hr
- Add C1 and C2 together and you will get a very simplified cooling capacity needed for the room as Estimated Cooling Capacity needed = C1 + C2 (BTU/hr)

**Other Factors**

Other factors that your contractor will consider to determine the sizing of the cooling capacity include the direction of your room. If the room is facing east or west, additional capacity is needed as it will be exposed to the morning and evening sun compared to a room that faces north or south.

If the lighting of the room emits a lot of heat, additional capacity is needed. If electrical appliances that generate heat is used, additional capacity has to be factored in. The type of material of the room and windows are also important consideration.