The right way to chose the proper size of an AC for your property

Comfort has become the root all needs. One such comfort that has become a necessity in today’s time is an Air Conditioner. The three basic functions of an air conditioner are lowering air temperature, removing air moisture and filtering the air. Along with these three basic functions, some ACs also offer functions like dehumidifier, reverse cycle for heating, odour remover,  sleep timer etc.

Air conditioners come in different types. Split ACs are made up of two units; an internal unit and an external unit. These are highly efficient and save space. Reverse system ACs provide cooling and heating function and thus can be used as space heaters during winters. Inverter ACs varies the temperature of the air they produce. These are cheap, quieter and achieve the desired room temperature more quickly. Multi-system ACs have multiple indoor units and a single outdoor condenser unit.

For efficient working, choosing a correctly sized air conditioner is very significant. A wrong choice in sizing can cause unnecessary problems; since the life of an AC is 10 to 15 years, you do not want to be stuck with a wrong one. If the chosen AC is larger in size than required, the AC will cool the room quickly without completely removing humidity leaving the room damp and clammy.  If the chosen Ac is smaller in size than required, it will not cool the room efficiently.

Energy Efficiency Ratio (EER) and Energy Star

Energy Efficiency Ratio or EER is the ratio of cooling capacity of the unit in BTUs (British Thermal Units) and the power input in watts that is taken by the unit. EER of the unit and its efficiency are directly proportional. The higher the EER, the higher is the efficiency of the unit. An air conditioner should possess an EER not lesser than 11. An increase of 1.0 on EER scale represents an increase of 10% on energy efficiency.

Having an Energy Star means that the product fulfils all the energy efficiency guidelines imposed by the Environmental Protection Agency and the Department of Energy. Energy Star qualified air conditioners use 15% lesser energy compared to the conventional air conditioners. They have timers for better temperature control and thus use the minimum amount of energy required to cool the room.

Cooling capacity and BTUs

BTUs approximately tells you how quickly and efficiently the unit will cool your home. Air conditioners are available in sizes ranging from 5000 BTUs (0.5 ton) to 36,000 BTUs (3 tons). The size of the conditioner is decided according to the per-square-feet area of the room to be cooled. Considering factors such as ceiling height, room insulation, sun exposure, location and your area’s climate is crucial too. Follow the table below to calculate BTUs required for your room.


Area to be Cooled
(Square Feet)


Capacity Needed

(BTUs per Hour)


100 to 150




150 to 250




250 to 300




300 to 350




350 to 400




400 to 450




450 to 550




  • If the room is heavily shaded, reduce the capacity by 10%
  • For rooms with excessive sunlight, increase the capacity by 10%
  • If installing the unit in the kitchen, add 4000 BTUs to the capacity mentioned in above table
  • If the number of people occupying the room are more than two, add 600 BTUs person.