Installing an air conditioner can make a big difference in how comfortable a home is during the hot and humid dog-days of summer. You need to make sure that you get the right size air conditioner for the size of your house, or it will run continuously without really cooling the house. Here is how you can calculate the size air conditioner unit you will need.
Measure each of your south side windows and figure the square footage of each (width times height). Add the square footage up and multiply it by 871 BTUs. Do the same for the north-facing windows and multiply the square footage by 166. Add these two figures together and write it down.
Walk around and look at your lights. Write down the number of watts per light and multiply it by 4.25 BTUs. For instance, a 100 watt bulb would generate 425 BTUs. If you have 10 lights, you would have 4,250 BTUs of energy being given off. Add all the amounts together and write the sum down.