Many people think the only thing that matters when buying an air conditioner is how big your house is. There are many other things that need to be figured if you want to have a system that is going to cool your home efficiently and continue to work properly for the life of the system.
It is actually best to find the floor size of each room and space that will be cooled by the unit. Multiply this number by 337 to find out how many BTUs it takes to cool that area.
The size of the north and south facing windows are also important to what size unit you need. Go through the house and figure the house and figure the area of all south facing windows. Multiply the result by 871. Figure the total size for the north facing windows and multiply the result by 166. Add the two end figures together. Save the number.
The number of people living in your home will have an effect on your AC efficiency. Multiply the number of people by 400 and save the result.
Lights give off heat and the heat will need to be overcome by your AC if you want your home cooled. Add together the watts used in all your light bulbs and multiply by 4.25.
Find out the wattage of each appliance in your home and multiply the total by 3.25.
Total BTUs Needed
Add together all the numbers from the steps above and you will have an idea of what BTU rating your system should have to keep your home cool efficiently. Do not go too far over this number as it will be too big and have its own set of problems.
Do not let a salesman tell you what size system you need based on the square footage of your home alone. The other factors that determine the size of your unit are just as, if not more, important. You do not want a unit that is based on house size alone because it will struggle to keep up with the demands you put on it and will end up requiring more servicing and being replaced much sooner than it should.
Once you know how many BTUs your home needs, you can start looking at different brands of air conditioning systems. Talk to your serviceman and find out if any manufacturer is offering an incentive for new purchases. You should also talk to your utility company to find out about help with getting an energy efficient model to replace one that is using too much energy. It may be in your best interest to get one with a higher SEER rating and get more help with the upfront cost. Check with the HVAC company about special financing to avoid paying a high interest rate. Keep in mind that a unit that is the right size will save you money over the years. The money saved will more than pay for the system.