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    wluo6129's Avatar
    wluo6129 Posts: 27, Reputation: 1
    New Member
    		  
    #1

    Dec 22, 2007, 08:15 AM
    Frequent activated furnace
    Dear experts:

    Recently I installed a new gas furnace (carrier 2 stage furnance). However, the furnace kick on and off frequently, i.e. short cycle. It turns on for 5 minutes and then turn off. After 10-15 minutes, it turns on again, and repeat the cycle. Is it normal? If not, how to solve this? It seems to me cost much more than my old 17-years old furnace.

    Thank you!
    acetc's Avatar
    acetc Posts: 1,004, Reputation: 79
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    #2

    Dec 22, 2007, 09:12 AM
    The heat anticipator in the thermostat may need to be adjusted, This applies to manual type thermostats, under the thermostat cover is an arrow pointing to a numbered bar , move it to a higher number and see if that helps.This new furnace may pull a higher amp draw through the thermostat then the old one. Good luck, Mike
    tsa7man's Avatar
    tsa7man Posts: 154, Reputation: 9
    Junior Member
    		  
    #3

    Dec 23, 2007, 12:40 PM
    If your furnace was set up properly by the install tech. with a two stage t-stat, it will operate as you indicated. It will run just long enough to satisfy the thermostat on low fire. If you need heat after a set time frame ( say 12-14 min's) where the thermostat is still calling for heat ( like in REAL cold weather) the furnace will kick into HIGH fire and give you the max Btu/hr that the furnace output is rated for to now heat your home. But, another issue could be that the furnace size is way over the correct BTU/hr capacity to heat your home,compared to your heat loss of the structure... then an oversized unit will short cycle like you stated.
    wluo6129's Avatar
    wluo6129 Posts: 27, Reputation: 1
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    #4

    Dec 26, 2007, 05:12 PM
    Thank you, Acetc and Tsa7man.

    My t-stat is digital 1-stage. It seems that there is nothing I can do to change the short cycle problem. The other question is that with this short cycle, will it increase my gas bill? Or it does not matter?

    Thank you! Really appreciate your answer!
    AC Doc's Avatar
    AC Doc Posts: 12, Reputation: 1
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    #5

    Dec 26, 2007, 05:27 PM
    The unit may be controlling the delay of the second stage by a time setting on the contol board. You may be able to set the aggressive setting on the thermostat to have it over shoot your setting to keep it off longer. You may also want to check behind the thermostat to make shure they sealed the wall to keep the air inside the wall from affecting the sensor.
    wluo6129's Avatar
    wluo6129 Posts: 27, Reputation: 1
    New Member
    		  
    #6

    Dec 27, 2007, 05:42 PM
    Hi, All:

    First, thank you for the answers you provided. They are really helpful.

    I tried to change the deadband setting in the t-stat from 1F to 2F. It did increase the cycle time, though I am not sure does it really save money. Hopefully this will work and save me some money.

    Again. Thank you for the help. Really appreciate it!
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
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    #7

    Dec 27, 2007, 07:24 PM
    Do you have a supply duct close by the thermostat that would be throwing the temp off on the t-stat. with a two stage gas valve it should not short cycle at all. They should have installed a two stage thermostat, but it will work with out it, by setting up the board correctly. It works off run time not temp before switching to high fire. It may be set up for just high fire.
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