To determine what size air conditioning unit you need to install in your house you need to contact a HVAC contractor. There are many factors to consider while installing a new cooling system in your house, the main factor being the load calculation. The load calculation should be determined by a mechanical engineer, or your HVAC contractor. A unit with a load lesser than what is required in your house will not provide you the desired comfort, more over the unit will be put to function longer hence will increase your energy bill. Insulating your home is also equally important to attain the maximum efficiency out of your cooling system. You need to insulate each and every part of your house, the walls, doors windows etc for increasing the efficiency of your cooling system. By doing so your air conditioner will run at an optimum amount of time thus will use the least amount of energy.
Installing a bigger sized air conditioner will also increase your energy bill. A bigger unit will force the compressor to work on a shorter cycle as the space will be cooled faster. When the compressor works in short cycles it will consume more energy. Frequent cut off will eventually cause compressor to overwork and later break down. Consulting a technician will help you determine the right load for your home. Many factors are considered while calculating the load of the unit. Do some research and find out ways in which you can make your cooling system function at its optimum efficiency.