Installing the right size equipment to heat and cool homes is essential to getting the best performance and comfort. A system that is too large will not keep the building comfortable because of frequent 'on/off' cycling. Incorrect sizing can also put stress on system components, shorten the equipment's life, and lead to wasted energy and money. To ensure proper sizing, builders should provide the homeowner a copy of the home's heat gain/loss calculations.
HVAC systems need to be properly sized so the home will be comfortable amid the harshest outdoor conditions. If a unit is oversized, energy costs may increase and the home may experience high temperature swings during milder weather. Oversizing also increases the equipment's initial cost, savings better spent on purchasing more efficient equipment. Determining the proper size for the HVAC system requires estimating heat loss (known as the design heat load) through the roof, walls, windows, basement, and other home components bordering unfavorable outdoor weather conditions. The system size is then matched to the design heat load. For many combustion appliances, the size of the unit selected will be 10 to 30 percent above design heat load. This oversizing allows the unit to recover quickly from night setback.
Tightly sealed ducting is also crucial to ensure high energy efficiency of HVAC equipment.
Residential Policy Options
- Equipment Sizing: Heating and cooling equipment shall be sized in accordance with Section M1401.3 of the International Residential Code.