When it comes to heating, ventilating and air-conditioning equipment, proper sizing is critical to the performance and efficiency of a system.

Although some homeowners feel a bigger system will do a better job, this isn’t always the case. For the system to perform optimally, it must be correctly sized by the contractor to meet the needs of the heating or cooling load.

If a unit is too large, its cycle times will be reduced. This prevents the unit from reaching maximum efficiency and, in turn, causes higher operating costs. It can also keep the unit from running long enough to remove excess humidity from the home, resulting in a decrease in home comfort.

If a house has an existing system that needs to be replaced, don’t assume that the new unit will be the same size and capacity as the old one. Changes in the home, such as additions, renovations and insulation, and changes in heating, ventilating and air-conditioning equipment, or HVAC, equipment, such as efficiency and technology improvements, may require a size different than the original.

Another way a contractor will determine the best-size unit is by conducting heating and cooling load calculations, using either the entire house or room-by-room calculations. The load is the amount of heating or cooling that the unit must supply to maintain a specified temperature.