Furnace only runs for 5 minutes


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Old 12-19-15, 07:50 AM
J
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Furnace only runs for 5 minutes

It's 20degF with a 1deg windchill outside. Overnight, stat is set to 65degF and then programmed to reach 69degF by 7am.

To go from 65 to 69, it ran nonstop for a good half hour or so. Now that it's 9am, it runs for 5 minutes, turns off for 10 minutes....and continually repeats.

Is this normal?

This is a 40Kbtu natural gas furnace, sealed combustion, in the basement. No registers in the basement, only on the main floor of this single story house. Basement is 80% insulated on the perimeter, temp in basement is 61degF. Static pressure across the electrostatic filter & furnace (excluding coil) is 0.5inwc. Temp rise measured at access holes close to the furnace was 115-69=46; spec is 35-65.

Doesn't even seem like 5 minutes is enough for it to effectively do anything except warm up the metal duct work. Even though the stat says 69, the air in the house still feels cold.
 
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Old 12-19-15, 08:08 AM
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It sounds like the furnace is operating properly. Two things to consider.

1-Move the stat to a location away from a register might help.
2-Another change is to lower the blower motor speed if the furnace has this feature. This usually involves moving a blower motor lead on a blower motor winding selection terminal (marked Hi. Med. Low).
Hope this helps.
 
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Old 12-19-15, 08:28 AM
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You don't say what type of thermostat you have but there are settings on most if not all heating thermostats that affect running time.
Old mercury and mechanical thermostats have a heat anticipator that you can adjust to set the furnace cycle time.
A heat anticipator will be found under the thermostat cover with an adjustment lever and usually the word "longer", meaning longer run time.

Digital thermostats usually have a dip switch or program where you set the thermostat for the type of furnace you have.
The simple non-programmable Honeywell digital thermostat we own sets the number of cycles per hour when you select the heating type.
It learns the preceding cycles and adjusts itself for the running time.
For our house it makes for very even temperatures.
 
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Old 12-19-15, 09:13 AM
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The temp rise on its lowest speed kind of cuts it close to the max (60F, limit 65F) and there's a weird smell on that fan speed...same smell that we got when the furnace was first put in. It's never hit the high limit (165F)...so I decided to leave it at the second lowest speed.

The stat is in a hallway that doesn't have any dedicated registers, just gets residual airflow.

In the past, I've taken the cover off the (Honeywell digital) stat before, looking for some heat anticipator switches and didn't find any & the owner's manual was just the basic instructions & figured it was hard-set.

Found the installation manual which mentioned a secret program where you gotta hit the up & down arrow for a couple seconds, and learned it is programmed for 5 cycles an hour. Gonna reduce it to 3 which the doc mentioned is recommended for 90% furnaces, of which I have. Let's see if that's all it took...thanks.
 
 

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