This tutorial will ask you questions about your home’s location, windows, ducts, and insulation. Based on your answers, it will generate an air conditioner sizing recommendation (smaller than, larger than, etc.) and a list of your answers that you can use to work with your contractor.

Some contractors will use rules of thumb to size your air conditioner, but rules of thumb can overestimate the size needed. A good contractor will use a design load calculation to size a central air conditioner to your home. The contractor will need to check the following six factors.

• How well your house is insulated? ~ By adding the proper amount of insulation to your walls and ceiling or attic, your house will require less cooling. By insulating before you purchase an air conditioner, you’ll save twice- once when your energy bills drop and again when you need a smaller, less expensive air conditioner.
• How well air leaks are sealed?~ A well-sealed house limits the amount of hot, humid air that gets inside. In many homes the air leaks can add up to as much as an open window. Sealing air leaks and adding insulation can reduce heating and cooling cost by 20%.
• How well your ducts are sealed and insulated? ~ Ducts carry cooled air from your air conditioner to where it is needed. Under-insulated ducts actually heat up, which reduces the amount of cool air that gets to you. Leaky ducts can cause your heating and cooling system to work harder to keep your home at a comfortable temperature.
• The size, type and number of windows and the direction they face ~ The size, type and number of windows are huge factors in determining your cooling needs. Thoughtful landscaping and overhangs can greatly decrease the temperature in your house by affecting the amount of sunshine that comes through your windows.
• Shading provided by overhangs and landscaping ~ Leafy trees can reduce unwanted heat in the summer, but allow the warmth of the sun to come in when they drop their leaves in the winter. Well-positioned overhangs will also block the sun’s heat in the summer, but allow the sun light to come in during the winter to warm your home.
• The size, layout, and orientation of your house ~ The size of a house’s walls and roof and their positions in relation to the sun are important factors in sizing an air conditioner.