I notice today that my new furnace will stop after about half hour and start again in a few minutes. The room temperature is 66 and I set it to 70. It took several stop and start before it reaches 70. What could be the reason, too heavy filter or not enough air coming back? The air filter is Honeywell Allergen Plus Pleated FPR 7 Air Filter.

  • Not likely. Why aren't you asking the installer to troubleshoot? – isherwood Nov 6 '17 at 1:43
  • The air filter is brand new. The unit was installed last year. – Luyin Sun Nov 6 '17 at 1:47
  • Well then... Tell us something about the filters before and after. Help us help you. – isherwood Nov 6 '17 at 1:49
  • @isherwood I am tired of working with them. If I know the cause I may do a better job than them. – Luyin Sun Nov 6 '17 at 1:49
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    The type of furnace is likely to be more instructive than the air filter. – Matthew Wetmore Nov 6 '17 at 3:25

The filter is only one aspect of an over heating furnace. The diagnosis is as simple as taking its temperature. Get a digital meat thermometer. Take the temperature at the inlet and the outlet of the furnace. All furnaces will have their minimum and maximum heat rise listed on the name plate. In leu of that number 50 degrees is a good middle ground. Subtract the inlet temperature from the outlet temperature. If it is within the specified range you are good. If it is really high like above 150 degrees you are likely tripping the high limit and need more air flow. Open all registers, remove the filter and put the fan to high speed. If the heat seems good and you have an analog thermostat it could be the heat anticipator is not set correctly. Analog thermostats have a small wire or coil of wire mounted near the mercury bulb or the bimetallic spring. It heats up a little to shut the heat off about a quarter to a half degree before the set point so it can glide to a stop. If it is set incorrectly it can shut off several degrees early. With the limited information you have provided those two suggestions are most likely but there could be any number of causes.

  • could also be a faulty flame sensor – Richie Frame Nov 9 '17 at 5:52

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