Furnace Short-Cycling

You're purchasing a home in Sunny Phoenix, Arizona and your home inspector says your furnace is short cycling. What!? Homes have furnaces in Phoenix!?

On a recent home inspection in Queen Creek, AZ (home of the Friday Night Feastival, a gourmet food truck extravaganza!) the furnace was short cycling. In other words, the furnace flame would only stay on for a few minutes and then go out. After a few more minutes the flame would re-ignite, and the process would repeat. In most climates this would be an obvious issue that doesn't take a home inspector to find, but here in the Valley of the Sun, the furnace may actually warm the home enough so that the occupants are comfortable and aren't aware that anything is wrong. 

So what is happening? In a nutshell, the furnace is trying to work but can't. There is some condition causing the furnace to detect a safety problem and so it shuts down and tries again. Poor air flow is a common reason for this, so check your air filters if this is happening to you. When the furnace is tested during a home inspection from Smart Start Home Inspections, we start the furnace by setting the thermostat to 90 degrees and listening for the air handler to come on. About ten minutes later, we will measure the temperature at one of the air registers. We expect to see some amount of heating at this point. Something above 90 degrees would be normal. The temperature is checked again in five minute intervals and expected to have increased from the previous reading each time. Normally, the temperature will climb continuously to about 120 - 140 degrees, but if the furnace is short cycling, the temperature will not increase and will most likely decrease compared to the previous reading. The short-cycling will be confirmed when we inspect the furnace itself and view the flames shutting down and re-igniting in a cycle. This is furnace short cycling, and should be further evaluated and repaired by a qualified HVAC contractor.

​Happy Inspecting!      

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