Determining the proper size heating and cooling equipment for your home is of the utmost importance and should be done only by a qualified heating and cooling contractor. Properly sized equipment will operate more efficiently, dehumidify better in the summer, humidify better in the winter, last longer and provide you with a more comfortable indoor environment to live in. To determine what size furnace and air-conditioner you need for your house we must first determine the heating and cooling loads on the house.
The first step in determining the load on the house is to measure the total wall area, ceiling area, floor area and glass area along with the direction each wall faces. The next step is to determine as accurately as possible the insulation value of the walls, ceiling, floors and windows. Once this information is known it is necessary to do a load calculation on the structure. We use a computer to enter the information about the house into the industry standard Manual J load calculation software and the calculations are done automatically. The information generated will tell us the heating and cooling load on the house in Btu’s/Hour as well as the heating and cooling airflow needed in Cubic Feet Per Minute (CFM) to allow the system to operate at rated efficiency. Although we prefer to use a computer for reasons of accuracy and speed a manual form can be completed to provide the needed information but takes quit a long time.
Once we know the heating and cooling loads on your house along with the airflow needed we simply pick a furnace and air-conditioner that will satisfy these requirements.
If the heating/cooling contractor giving you an estimate can’t tell you what the heating and cooling loads on the house are (in Btu’s/Hour), what the airflow requirements are (in Cfm) along with how the information was calculated it means they just guessed. Realizing the importance of installing the proper size heating and cooling equipment I’m sure you don’t want someone who is just guessing installing your new, and expensive, home comfort system. Don’t let someone tell you they know what size furnace and air- conditioner you need because they have been doing this for years. Most contractors who guess end up installing equipment that is too large for your house.