Steps a Good Contractor Should Take to Size Your System Many factors affect a home’s heating or cooling requirement, or “load.” A good estimator will measure walls, ceilings, floor space, and windows to determine the room volumes, and will assess the R-value of the home’s insulation, windows, and building materials. A close estimate of the building’s air leakage is also necessary. A good estimate will also include an inspection of the size, condition of seals on joints and insulation, and location of the distribution ducts in forced air systems. The placement of supply and return registers should be appropriate for the system type and size. The orientation of the house also affects heat gain and heat loss through windows. Overhangs can reduce solar gain through windows. Make sure the contractor uses the correct design for the outdoor temperature and humidity in your area. Using a higher summer design temperature results in oversizing air conditioners. A good contractor should:

• Use a computer program or written calculation procedure to size the system

• Provide a written contract listing the main points of your installation that includes the results of the heating and cooling load calculation

• Give you a written warranty on equipment and workmanship

• Allow you to hold the final payment until you are satisfied with the new system.

Even the most energy-efficient heating and cooling system will fail to save you money if it is the wrong size for your home.