Q. Our buyers hired a home inspector. When he was here, the outside temperature was 105 degrees. After he tested the heating and air conditioning system, the outside condenser stopped working, and that night our house got up to 91 degrees. Our HVAC contractor found a blown fuse in the condenser, and he said the inspector might not have followed "standard power cycle procedures." Because of this, we question the inspector's report on our system. His report says, "The furnace data plate indicates a temperature rise of 45-75 degrees. When tested, the rise was approximately 35.9 degrees. This is not within the manufacturer's recommendations. Routine maintenance by a qualified HVAC contractor is advised." Is this finding reliable, and can temperature rise be reliably measured when the summer temperature is over 100 degrees?
A. Testing the temperature rise in a forced air heating system is highly unusual for a home inspector because it exceeds the standards of practice of the profession. Home inspection addresses the safety and functional performance of a heating system, not its technical accuracy. A heating system that emits air 35 degrees warmer than the ambient temperature will effectively heat a home in a normal and reasonable amount of time. One question that arises is whether the home inspector's measurement of temperature rise is accurate.
Temperature rise in a forced air heating system is the difference between the ambient temperature in the house and the temperature of the air as it leaves the heat exchanger inside the furnace. In order to read the output temperature at the heat exchanger, specialized testing equipment is needed. The inspector in your home may have had such equipment or he may have measured the output temperature at one of the registers in the house. At those locations, the temperature rise would not be as great, and the measurement would be invalid.
Your contractor also suggested that the condenser fuse may have blown because the inspector might not have used "standard power system procedures." This procedure is simply to allow a few minutes after the heating system has turned off before turning the air conditioning system on. Switching immediately from one function to the other is called "short cycling." Actually, the inspector may not have caused the fuse to blow because most thermostats have timed lockouts that prevent short cycling. The fuse may have blown because the system was having to work continuously on a very hot day. Fortunately, you have already complied with the inspector's recommendation to have routine maintenance by a qualified HVAC contractor.
Q. I read one of your archive articles about ventless gas-log fireplaces and have just one question. Are they safe or not?
A. Ventless gas-log fireplaces are safe in nearly every case. My issue with ventless fireplaces is not the likelihood of failure. It's the manufacturers' claim that these fixtures are fail-safe. In my opinion, nothing man-made is fail-safe. Instances of failure with ventless gas fireplaces are very rare, but they do exist. If you purchase one, just be sure to install a carbon monoxide detector nearby.
• Email questions to Barry Stone through his website, housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.
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