When it comes to buying and installing an air conditioning system it is essential that you get the sizing right, air conditioning is expensive so it is imperative that you get it right and do not make an expensive mistake. There are many ways in which a room accumulates heat and all of these have to be taken into account when it comes down to determining the size of the unit you need.
First of all heat is of course generated by the amount of occupants in the room or house, however many other factors have to be taken into consideration including computers, TVs, the lighting in the home, air that enters through open doors and windows, internal heating and the sun beating down on the house. It is the heat load which must be calculated in order to find the right sizing for air conditioning.
Calculating Heat Load
There are many different ways in which you can calculate the heat load in your home or room, one of the quickest ways which will give a quick estimate when it comes to sizing based on 4 people in the home and average heating is to measure in feet the length, width and height of the room and multiply this by 4.
However a far more accurate method although more complicated method of making this calculation is to take many other factors into account. Factors you should consider include
• The heat which is generated by all lighting
• Where the windows are located in the house, the size of them and whether they are shaded
• How many occupants are in the house and consider if this would change in the future
• The size of the area which you want cooling
• All electrical equipment and any you might purchase in the future
This method is more complicated because you will have to make a calculation from each individual item and then add them together. While this is time consuming it is a very accurate method of getting estimation for the sizing of the air conditioning you need.
Steps for a More Accurate Method of Air Conditioner Sizing

• Measure in feet the area which you wish to cool, take measurements for the length and width then multiply this by 31.25
• Next calculate the windows, if they are not shaded then multiply the end result by 1.4. If your window is facing to the North then measure the sq feet and multiply this by 164. If the window faces South then measure the sq feet and multiply by 868.
• Next calculate the heat by the people living in the accommodation, to do this you have to multiply the total amount of people by 600
• For appliances you have to add the wattage of every appliance together then multiply the total wattage by 3.4
• Find the total amount of watts for all the lighting in your home and then multiply this by 4.25
• Finally once you have noted down all of the above factors add them together to determine the total amount of heat load in your home.
Once you have an estimate then all you need to do is to divide the total heat load you just figured by the cooling capacity of the air conditioner making sure you are looking at the BTU of the unit, following these steps you will be able to find the correct sizing and know how many units you need. While the above can sound a little complicated and time consuming, it is actually going through this process due to the expense of installing air conditioning.