There are many different types of heat pumps and efficiencies, but there is another important factor if you’re considering a new unit—purchasing a properly-sized unit. Because your heating and cooling system is one of the more costly purchases for your home, it is important to understand how to know your unit is the correct one.
When dealers talk about the size of a heating and cooling unit, the measurement is in tons, where 12,000 BTU/h equals one ton of heating and cooling. There are a few ways a dealer can determine the size unit needed for your home: replacing the old unit with the same size, using a “rule of thumb” or performing a load calculation, which is the best method.
In many cases, when it’s time to replace a unit, dealers will typically put in a system that is the same size as the previous system. But if you have made any kind of energy efficiency improvements to your home, the unit may not be the right size for the current household and could be oversized. When it comes to your home’s heating and cooling system, bigger isn’t always better. Not only would you pay more at the point of sale for the unit, but down the road, you may be paying higher power bills since your system will not be as efficient as it should be. Another method to sizing a unit is to use a “rule of thumb” where the unit is determined mostly by the square footage of a home. This is something that has been done for many years and often leads to the installation of an oversized unit, since using this option does not take into account any aspects of the home, such as insulation levels or types of windows and doors, which should also be considered when determining the size of the unit needed.
The most accurate way to determine the size needed for a home is to do a load calculation. Air Conditioning Contractors of America (ACCA), the governing body for air conditioning contractors, developed a manual for contractors to follow in order to determine the size of a unit— the Manual J. The Manual J load calculation takes several items into account to determine the size of the unit, including the dwelling’s square footage, volume of the home, size and type of windows, doors, walls and floor, the direction the house faces, type and amount of insulation, number of people living within the home, air infiltration, appliances and more to accurately determine the amount of BTU/h needed to properly and efficiently heat and cool the home. Once the BTU/h is determined, ACCA developed additional guidelines for selecting equipment and designing the duct work. There are several programs contractors can use that follow these ACCA-approved principles.
When you receive quotes from contractors, remember to ask how they determine the proper size of the unit. They should do a load calculation, verify the duct is designed correctly and pick the appropriate equipment.
Remember, a properly-sized unit will mean that you are getting the most value from the power you and your family consume.