Airco AH-90MD runs a lot

[cboey]

Hi, I have an Airco AH-90MD. It seems to cut in and out more often than it needs to. In the mornings, it might run for 5 mins, cut out for 3-4 mins and then run again.

House is bilevel around 1050 sq ft on the main floor. I'm wondering if it's undersized for the sq footage of the house or what else might be the problem?

[John Kogel]

Your best bet is to have it serviced if that has not been done. The furnace might be cutting out for reasons other than temperature.

Is there any soot around the front where the burners would be, or around the vent?

[cboey]

Ok. No there's no soot at all.

Also, what is normal running time for furnace to get house to temp from 19 degrees overnight to 21 degrees? If it takes half an hour, is that a long time?

[inspector57]

Time is all relative and no general rule of thumb should be used.

Have the unit serviced and determine if it is cycling on the thermostat or other safety switch.

For a properly functioning system, in general "on" time for any heat source is determined both by capacity of the furnace as well as the "load" of the house in which it is installed.

The "off" time is determined solely by the effective insulation of the structure in relation to the temperature difference between indoor and outdoor temperatures.

So run time is determined by the furnace and

off time is determined by the house.

A properly sized system will run almost continuously at design temperature, which is generally the historically coldest temperature for your location.

[cboey]

Yes, that makes sense. Thanks!

[Jim Katen]

Crank the thermostat up to 27 or 28.

If it continues to short cycle (run for 5 minutes, turn off for 3-4 minutes, and run for 5 minutes again), then it's probably shutting down in response to the high temperature limit switch. In that case, before doing anything else, try changing or cleaning your filter.