# Furnace takes forever to heat house



## kkollins (Nov 17, 2011)

I have a well insulated home built in 2000. My gas furnace is properly sized and the filter is changed every 6 months. At night I drop the temperature on my digital thermostat to 61 degrees, in the morning I have it set to 69. It takes over 3 hours to get the house up to that temperature. The reason, the furnace will kick on and run for approximately 15 or 20 minutes then shut off. The temp goes up a degree or 2. Then it's off for approximately 15 20 minutes and does it again and then will turn back on and run again for 15 or 30 minutes. It keep doing this until it gets to the desired temp. FYI...once it get there, it will hold the temp no problem.

Someone said it's because it's a hi efficiency furnace that it will only take the temp up a few degrees at a time? That doesn't sound right to me. Any ideas on if this is normal and if not what would be causing it?


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## Doc Holliday (Mar 12, 2011)

Hi efficency furnaces first run blower speed in low for dehumidification purposes. There are switches on the control board which you can adjust how long the low speed is timed for, anywhere from approximately one or two minutes to over 7 minutes. Sounds like yours is set for either near or full maximum low speed run time.


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## harleyrider (Feb 20, 2007)

many things could be the culprit, a couple real good possibility's are the furnace is cycling off on the high limit and/or the flame signal to the control board is low. one other real possibility is that the condensate is draining slow, when was the last time the unit was properly serviced?


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## biggles (Jan 1, 2008)

is that 69F a "wake up" time setting?if your not set at the time you wake(feet hit the floor) up the stat will tweek the temperature so your at 69F at your chosen time other then waking up in the morning


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## kkollins (Nov 17, 2011)

The unit was serviced last year when I had a bird get into my exhaust and die. It's a "wake" time....I want it at 69 degrees by 6:30am. So I originally had it wet to "wake" at 6am thinking 30 minutes would be enough to raise it 8 degrees. However, I now have moved it back to 5am and it still doesn't hit 69 degrees until 8:30ish. This morning I went down and manually flipped the on off switch on the furnace and did notice that it ran continually for maybe 30 minutes until it hit the 69 degree mark...I think it was at 65 when I flipped it, so it ran it up 4 degrees. So "manually" flipping the switch on the furnace forced it to start and then it stayed on.


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## REP (Jul 24, 2011)

It sounds like a thermostat problem.
Differant thermostats by differant makers react in differant ways.It depends on the intelligence that is built in to it.
I suggest you get your owners manual out and study it.The answer should be in there somewhere.
Also in some select furnaces there are differant programs that "learn" to operate in a certain way.
It could be under the right combination that you stst and furnace are trying to learn a pattern for you.
Ahhhh I long for the days of a good old T87 off and on control.LOL


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## sammy37 (Dec 9, 2008)

It may be a high limit issue but hard to tell, may also be a bad thermostat.
If you are only changing your filters every 6 months, then that might explain a high limit issue. You should change your filter once a month.


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## biggles (Jan 1, 2008)

sounds like the stat is having a problem anticipating the temperature called for at the time selected waking up what is the stat model number if yuo have wake/leave/return/sleep modes what are the other temps during the day and night.if you do a leave temp when the house is empty...how's it walking in from work...might be a sub menu for the recovery..the one thing with any heating cycle the fan is controlled thru the furnace delay or heat fan limit to run it.the stat doesn't control the fan in the heating modes...


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## Technow (Nov 12, 2010)

What furnace do you have?
What thermostat do you have?
Are the temps in your area the extreme (coldest) or some other?


If the furnace is shutting off before setpoint of thermostat there is a problem.


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## biggles (Jan 1, 2008)

pull the stat and jump R to W and tell us if you get solid heating cycle...run...do not :no: reset the power... down on the furnace


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## harleyrider (Feb 20, 2007)

kkollins said:


> The unit was serviced last year when I had a bird get into my exhaust and die. It's a "wake" time....I want it at 69 degrees by 6:30am. So I originally had it wet to "wake" at 6am thinking 30 minutes would be enough to raise it 8 degrees. However, I now have moved it back to 5am and it still doesn't hit 69 degrees until 8:30ish. This morning I went down and manually flipped the on off switch on the furnace and did notice that it ran continually for maybe 30 minutes until it hit the 69 degree mark...I think it was at 65 when I flipped it, so it ran it up 4 degrees. So "manually" flipping the switch on the furnace forced it to start and then it stayed on.


 This statement tells me clearly that its not a t-stat issue, reseting the power clears the memory on most main boards, thus clearing any faults. The furnace will run 1 cycle, learn a fault and then error out again. I am thinking its a dirty flame sensor, but of course with out being there to measure the signal its just an educated guess.


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## HVACDave (Oct 16, 2007)

Could be a flame sensor, but then you would typically only get the burners on for a few seconds at a time, and occassionally get a full cycle. It could be any of the ussual suspects, plugging condensate line, restriced vent line, dirty pressure switch connection to vent box, tripping on high limit due to dirty filter/AC coil etc. 

The OP should check to see if during this 4 hours of run time there is warm air moving through the heating registers consistently, or if all they know is that the fan seems to be on forever and never checked the temps of the discharge air.


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## harleyrider (Feb 20, 2007)

HVACDave said:


> Could be a flame sensor, but then you would typically only get the burners on for a few seconds at a time, and occassionally get a full cycle. It could be any of the ussual suspects, plugging condensate line, restriced vent line, dirty pressure switch connection to vent box, tripping on high limit due to dirty filter/AC coil etc.
> 
> The OP should check to see if during this 4 hours of run time there is warm air moving through the heating registers consistently, or if all they know is that the fan seems to be on forever and never checked the temps of the discharge air.


I agree 100%


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## kkollins (Nov 17, 2011)

Thanks guys...got it fixed...it was the simplest of them all...dirty filter. Replaced that and it fired right up and heated up the house in about 30 minutes. I apparently fell victim to marketing. On the filter it says "Lasts 6 months" HAHAHA...it was SOOOO dirty....I'll be changing it monthly from now on.! Thanks again!


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## biggles (Jan 1, 2008)

so it was going off on HI limit with that blocked filter...trick of the trade if you hold it up to the light can't see light thru it change it....check those squirrel fins of dirt and dust if its bad move onto the A coil if you have cooling......they all catch dirt/dust once it gets past the filter......:whistling2:


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## harleyrider (Feb 20, 2007)

kkollins said:


> Thanks guys...got it fixed...it was the simplest of them all...dirty filter. Replaced that and it fired right up and heated up the house in about 30 minutes. I apparently fell victim to marketing. On the filter it says "Lasts 6 months" HAHAHA...it was SOOOO dirty....I'll be changing it monthly from now on.! Thanks again!


check post #3 

and a side note.....any 1 inch thick filter, reguardless of what the package says......should be replaced every 30 days.


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