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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 blower door test is the best way to measure air leakage.

A good estimate will also include an inspection of the size, condition of seals and joints, insulation, as well as the location of the distribution ducts in forced air systems. The placement of supp1y 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.

When the contractors are finished, get a copy of their calculations, assumptions, and the computer printout or finished worksheet. This is your only proof that they did the job right. To summarize, when designing your new heating and air conditioning system, the contractor you choose should do the following:

  • Use a computer program or written calculation procedure to size the system
  • Provide a written contract listing main points of your installation and 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.