Furnace cycle times

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  #1  
Old 10-14-05, 10:31 AM
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Furnace cycle times

As we enter into another heating season I am reminded of an annoyance I've had with my 2 year old house. I have a 90+ Bryant propane forced air furnace and Honeywell programmable thermostat. Since its been installed I have noticed cycle times where the furnace will run for 3-4 minutes at a time, shut down for about 10-15 mintues, and then fire back up. This seems awfully inefficient. The house is well insulated, Anderson double pane windows, and tight.

I think the reason it is running like this is that it is trying to keep the house exactly at the temperature that is set. I thought normally there is a range (say + or - 2 degrees) that thermostats control. There is no adjustment for this on the thermostat. Is this normal? If not what should I do? Thanks for the help.
 
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Old 10-14-05, 11:31 AM
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This is a common complaint for the Honeywells. The thermostat should have adjustments (internal screws or dip switches) for the type of system you are running. See the manual, or go to Honeywell's website if you don't have the manual. My CT 3300 stat cycled way too frequently with the "correct" system setting, sometimes ending the call for heat even before the burners had heated the plenum enough to turn on the blower fan, particularly in milder weather. Although I have an 80% forced air, I reset the system type to hot water, which reduced the cycle rate from ca. 6 times per hour to ca. 3 times per hour. Although there is a bit more temp variation in the house, the longer cycle times result in higher efficiency and less wear on the equipment.
 
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Old 10-14-05, 11:43 AM
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Wink

You dont say what tstat you have there. But you have to push up the anticipator on it if you have one. On some tstats you have to check and see if its set for gas oil or electric heat.

ED
 
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Old 10-17-05, 05:20 AM
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Thanks for the responses. The model I have is a T8002. After doing more research I have been able to find the installation manual on the web. In it they suggest 3 cycles per hour for a 90+ gas furnace. I have the option of choosing 1,3,4,5,6,9,or 12 cycles per hour. Does the 3 cycles sound right? Thanks again.
 
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Old 10-17-05, 07:03 AM
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Yep, 3 is what you want.. That's what I got ours at. Was it set at 6?
 
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Old 10-17-05, 01:27 PM
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My honeywell was set on 6 an it was a 1 deg rise, set it on 3 and went up 2 deg.
 
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Old 10-18-05, 09:35 AM
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It was set at 6 which is probably a factory setting as my heating contractor had no clue on how to adjust it. Thanks for all the help.
 
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Old 11-15-05, 07:59 AM
kitten
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I have the same problem with my Honeywell CT3500 thermostat. And the installation manual doesn't say how to change the cycle rate. Can anyone help me? Thanks.
 
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Old 11-15-05, 08:26 AM
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Look to make sure heat anticipator setting is not set below .4 (point 4). (You could temporarily bump it up to say .6, to see if that affects it)

Make sure you don't have heat blowing on the thermostat like from some nearby heat register whose air current takes it to the thermostat and keeps tripping it out.

Check to see if furnace is high limiting. IF you have a Honeywell fan switch, it's easy to see if you take the cover off that is held on by one screw ontop, and see that the dial does not spin over to by the high limit setting (the last pointer setting on the dial. (The first setting is the fan 'off", the 2nd pointer setting is the fan 'on', and the 3rd pointer setting is the high limit of the furnace where the furnace flame gets intentionaly put out, but the blower wil continue to run to help cool down the overheated heat exchanger. Note that the settings on the dial wil turn with the dial (never try to turn that dial!) and then these are read by observing where these settings are in relation to the stamped line that is on the stationary plate of the switch.
 
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Old 11-15-05, 09:53 AM
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Originally Posted by Bonehead
Look to make sure heat anticipator setting is not set below .4 (point 4). (You could temporarily bump it up to say .6, to see if that affects it)
Electronic tstats don't have heat anticipators.

Nor do any of the 90+ furnaces still use a fan limit control.

It is all solid state timers now.
 
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Old 11-15-05, 02:28 PM
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Originally Posted by kitten
I have the same problem with my Honeywell CT3500 thermostat. And the installation manual doesn't say how to change the cycle rate. Can anyone help me? Thanks.

http://www.golennox.com/support/Hone...500_CT3595.pdf

Go to system set up in the manual, and set it up to your system..

I'd suggest 3 for newer system.
 
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Old 11-17-05, 07:05 AM
kitten
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I have the user manual. So I should set the System Type(Feature number 4) to 3, right? There are four options for this setting:

1 = Gravity or steam system.
3 = Hot water, high efficiency furnace (90% or better), or single stage heat pump.
6 = Gas or oil forced air furnace (preset).
9 = Electric furnace.

Is there any negative effect on the furnace when it is set to 3? The user manual doesn't give the details about what these options mean. What happens if I set it to 1? Longer cycle time?

Thanks for your help.
 
  #13  
Old 11-17-05, 07:45 AM
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No negative effect -- the only thing these settings affect is how frequently the furnace will cycle. 3 is probably right. If you set it to 1, you are likely to find that the furnace doesn't cycle enough (long run time, with long off time in between), resulting in unacceptably wide temperature swings in the house.
 
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