Q. Late last summer, our air conditioner was not doing a good job of cooling, but we decided to save through the winter and have a new air conditioner installed this spring. I have received several estimates on what we need to do to upgrade. We have a 1980s two-story home with an unfinished basement. One contractor wants to replace the air conditioner only. Some want to replace the furnace and air conditioner, and one wants to replace everything including most of the ducts. What should we consider in making a decision?
A. The easiest and most economical choice would be to replace the air conditioner only, but that may not be in your best interests in the long run.
If your plans include remaining in the home for five years or longer, you really should consider a total upgrade. Your question concerning an air conditioner leads me to believe the home is heated by natural gas and not an electric furnace, so my answer will be concentrated on a gas-forced air-heating system.
There are so many variables with each home that the first thing you should do is have an energy audit performed. An audit will determine such things as: Do you have the required insulation? Is the home substantially airtight? An auditor may test to see if a home has a large amount of leakage of the conditioned air to the outside air or if the ducts have air leakage inside the home.
It's critical for the house and the HVAC system to work together, and you can't depend on the HVAC system alone. There is a guide to DIY energy audits at energy.gov/energysaver/articles/do-it-yourself-home-energy-audits. But for such a large investment, you should use the services of a professional, certified by BPI (Building Performance Institute Inc., at www.bpi.org) or RESNET (Residential Energy Services Network, at www.resnet.us).
With a total upgrade, the contractor will determine if the existing ductwork is sized properly for the furnace fan, and where the furnace is located in the home.
As I have stressed in past articles, when a furnace is located in a basement, it is difficult to cool the second-floor rooms, because the colder air is dense and does not rise as easily as warm air. With a new high-efficiency furnace, the furnace can be relocated to anywhere inside the home or attic to better cool the second-floor rooms. You should choose an HVAC (heating, venting and air-conditioning) contractor who uses the HVAC manuals designated for the sizing, placement and installation of the ductwork and for the proper sizing of the heating and cooling equipment.
One home I recently inspected had a 4-ton air conditioner for a 1,900-square-foot ranch-style home. In my opinion, the air conditioner was oversized and would quickly cool the home, but would do little to remove moisture from the home's air. A damp home is a breeding ground for mold and mildew.
I also found that the inside coil, which is part of the cooling system and located in the furnace cabinet, was not designed for a 4-ton system. All components of the HVAC system need to be matched to work efficiently, quietly and provide the most comfort for the homeowners.
If possible, all the ductwork should be located inside the home and not in an attic, attached garage or crawl space, and all of the ducts must be sealed airtight at all joints and seams.
Even though this has been a code requirement dating back to the 1980s, few contractors in my area bothered with sealing the ducts then, but the "times they are a-changin' " -- and the new codes are being rigidly enforced. If advised by the energy auditor, a total upgrade would be an economically wise choice.
Ÿ Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at d.Barnett@insightbb.com.
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