# Problems with new furnace..Overheating, having to reset. Furnace too big?



## kennzz05 (Nov 11, 2008)

sounds like its as simple as a bad rollout sw. being over or undersized has no bearing on the rollout. thats there to protect you from carbon monoxide or dirty heatexchanger or any situation where the flames could leave the heat exc.
and based on your story you stated its tripping when the unit isnt running, sounds bad to me

located inside the cabinet on the rating sticker you should see the words heat rise than a temperature value for example:45-75 
this means when the unit is running and up to operating temp, the differance between return air and supply air should be between 45-75 degrees of each other. example:ret/air temp 70. supply air temp125
as long as youre within this range your furnace isnt over/under fired.
make sure you dont take a temp reading where there is any infared heat
for example take your reading several feet away from the furnace


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## Tommy2 (Nov 25, 2008)

kennzz05 said:


> sounds like its as simple as a bad rollout sw. being over or undersized has no bearing on the rollout. thats there to protect you from carbon monoxide or dirty heatexchanger or any situation where the flames could leave the heat exc.


Thanks for the reply. I'll probaly go ahead and buy one. (should be cheap enough) before putting anymore time into it. 

The flames look good..but, its somewhat hard to see all of them clearly through the little eye piece. And I cant imagine how they could not be going into the heat exchangers. Slipping the manifold/orifices in place was pretty much idiot proof. 
Unless the gas press changed after the furnace fired a few times. (it said in the instructions to adjust the press after firing a few times..gas company did it only once) 
But they do this all day everyday..So you'd think they got it right.


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## Tommy2 (Nov 25, 2008)

Just did it again..Furnace was off for five minutes. Then the blower started up. (no call for heat)

So I guess I should replace the roll-out switch.


The temperature coming out of the furnace feels "normally" warm. Basically the same as the old oil unit.
The air duct on top the furnace gets warm, but not to where it would burn you. Pretty much what you would probaly exepct.

Also, the furnace exhaust (and intake) 3" pvc blow/suck fine..Condensate is fine as well.

Oh, and I felt the burner cover where the roll out attatches to. It does not get very warm when furnace is on. About the same warmth of the ducts.


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## pipefitter636 (Nov 1, 2008)

Tommy2 said:


> Some backround first. Cliffnotes on the problem below.
> ..
> 
> I should mention too that I have 2 working carbon monoxide sensors in the house(never went off..incase someone is thinking bad heat exchanger)
> Just because the carbon monoxide detector didn't go off doesn't mean that the heat exchanger isn't bad. A flame rollout is serious and should be checked by a professional. You went this far and saved alot of money,so if you want to be safe and live to tell about it have it checked by a professional. Manual resets are there for a reason(to get your attention that there is a problem)


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## Tommy2 (Nov 25, 2008)

A bad heat exchanger on a brand new furnace? This switch doesnt actually "detect" carbon monoxide, right? Its just senses heat? And the panel its mounted to does not get beyond "warm".

Talked to the supplier I got the furnace from. He told me to notice the code flashing on the control board. It just looked like a continuous flash..But Im running the furnace again to see if it can trip the code again, just to make sure.

Of course, now for the first time its working perfectly and I can't get the roll out to trip again lol. Running fine the past few hours set a few degrees higher than before too.

I pulled out the roll-out and looked it over. Maybe just handling it a bit, knocked something loose in it so its working right.

I cant get over how flimsy these switches are. Im a car guy, and Im just shocked at how flimsy some of this crap is. That switch is a joke. The button is just loose feeling.


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## beenthere (Oct 11, 2008)

Are you sure its not pulling its own exhaust back in.


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## Tommy2 (Nov 25, 2008)

beenthere said:


> Are you sure its not pulling its own exhaust back in.


Hi, No, shouldnt be. The pipes exit the house with the exhaust on top, intake below. The intake has a 90* downward termination, and the exhaust has a 45* horizontal termination.
Not quite cold enough to see the exhaust real well, but I'll check it again when its colder out..Then you can see the warm exhaust much better.


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## hvaclover (Oct 2, 2008)

You didn't change the motor speed correctly which could account for the intermittent tripping.

Nordyne (Tappan)is my line so I can speak with some authority here.

Look in your instructions on how to change motor speeds and take a temperature rise from the supply and return.

Also describe how you ran the PVC with how many elbows per each run.

Post the distance between the out door terminations.

Been there could be right too, it may be recirculating exhaust wind the wind changes.

Get back to us with the info i posted.


Also possible to have a bad LP regulator.


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## Tommy2 (Nov 25, 2008)

hvaclover said:


> You didn't change the motor speed correctly which could account for the intermittent tripping.
> 
> Nordyne (Tappan)is my line so I can speak with some authority here.
> 
> ...


Thanks for your reply.

How do you change motor speeds on these Tappans? Could you please explain it?
In the instructions it says "please refer to your furnace instructions for how to change the blower speed" THOSE ARE THE INSTRUCTIONS! :laughing:
So, I just assumed it amounted to moving the leads over.
There is virtually no information on how to change the motor speed other than the wiring diagram.

What exactly did I do by moving the leads over?

The PVC run is fine. Its about 20ft each pipe 2/3 bends per pipe. Upward slope, etc, etc. By far within spec since I used 3 in pipes.

The distance between outdoor terminations is probaly over a foot. Its possible the winds could effect it some, and the intake could get a slight breath from the exhaust..but would that effect the switch tripping after the furnace is done cycling?

I do not have a thermometer to check vent temperatures. (guess I need to get one) I can only assume that I need a higher than factory fan speed (or atleast it wouldnt hurt anything) when using a fairly large (possibly oversized) furnace.


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## hvaclover (Oct 2, 2008)

Jeeze...


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## Tommy2 (Nov 25, 2008)

hvaclover said:


> Jeeze...


What did I say?

If theres any Nordyne experts - please describe how to change blower speeds properly. Ive been searching the net, and can't seem to find anything.
Can't believe it's such a mystery heh.


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## hvaclover (Oct 2, 2008)

i said "Jeeze" cause i just dawned on me I am under legal obligation to my furnace line not to go beyond what advice I have already given you.
Sorry. 

The directions can be obtained from who ever you bought the furnace from.


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## Tommy2 (Nov 25, 2008)

hvaclover said:


> i said "Jeeze" cause i just dawned on me I am under legal obligation to my furnace line not to go beyond what advice I have already given you.
> Sorry.
> 
> The directions can be obtained from who ever you bought the furnace from.


Well, thats no problem. I just wanted to make sure I didnt offend you somehow! :laughing:
(dont want to upset anyone).

At anyrate..I think I actually might understand it now. The m1, m2 and m3 terminals are "unused". The instructions say this, but I didnt understand why.

To adjust the blower speed, you have to palce a different wire into the "heat" tap. Which makes perfect sense. Looks like black for high, blue for medium high, orange for medium low, and red for low(the current wire). 

So, I should get a good thermometer and set the speed correctly.

The instructions were a joke for this though. Zero direction..


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Well, thats no problem. I just wanted to make sure I didnt offend you somehow! :laughing:
> (dont want to upset anyone).
> 
> At anyrate..I think I actually might understand it now. The m1, m2 and m3 terminals are "unused". The instructions say this, but I didnt understand why.
> ...


:thumbup::thumbup::thumbup::thumbup::thumbup::thumbup:


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## Tommy2 (Nov 25, 2008)

Good good good..I think I'm getting somewhere now. 
Thanks for pointing me in the right direction. 

If the temp rise turns out to be too high..I bet adjusting the speed will take care of it..

I may add another basement duct too...Just for the fun of it. Make sure all warm air is getting expelled.

Edit: looks like the blue wire is actually attached from the factory on this unit (medium high). I kinda doubted it was on a lower setting considering how hard it seems to blow..
So, theres atleast one faster speed I can use if my temp readings indicate too high of a temp rise.


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Good good good..I think I'm getting somewhere now.
> Thanks for pointing me in the right direction.
> 
> If the temp rise turns out to be too high..I bet adjusting the speed will take care of it..
> ...



A jumper comes in the parts bag.Jumper between heat and cool and just use the black wire. It'll operate on high speed in heat and a/c


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## Tommy2 (Nov 25, 2008)

Yep. I actually dont have AC, so that makes it even simpler, heh.
Thanks


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## beenthere (Oct 11, 2008)

What size was your old furnace.


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## Tommy2 (Nov 25, 2008)

I think it was around 75,000 btu...but I was too stupid to know how to read the tag before I bought my new furnace. 
I just asked the counter guy at the furnace supply store what size would be good for 2500 sq ft(just to ballpark it) and he said 100,000 for a high ef.

I think he must have been assuming you need 40 btu for every sq ft. The more research I do, it seems like 30 is a little more accurate. Of course, this is all ball park talk. You have to take into consideration ceiling height, duct work, etc, etc..

Basically..It seems like you'd be better off going a little too small than too big.


I'll also say the furnace hasn't tripped since yesterday..Running plenty too. 
Happy about that..


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## beenthere (Oct 11, 2008)

Lot of houses work out to 22 to 25 BTU per sq ft.

So, yea, you are grossly oversized. 
Most counter guys have no idea how to size a furnace.

You may still be exceeding allowable temp rise.
You might want to add more return and supply to it.


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## hvaclover (Oct 2, 2008)

100k is not "Grossly" over sized Been.


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## beenthere (Oct 11, 2008)

hvaclover said:


> 100k is not "Grossly" over sized Been.


It is if he only needed a 60,000 BTU.


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## hvaclover (Oct 2, 2008)

beenthere said:


> It is if he only needed a 60,000 BTU.


He said his home was drafty.....uhhhh I assumed he meant badly insulated.

With poor insulation I got 111kbtu.

2500x 40/.90


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## Tommy2 (Nov 25, 2008)

Yea..I can't possibly imagine 60,000 being big enough - unless the home was super tight. 
I live in a 35 y/o home with original single pane windows. Insulation isn't bad(not perfect either)..but the windows are terrible. I'll get around to replacing them eventually..

80,000 probaly would have been just fine.

You live and learn. Cant get a new furnace now..Stuck with making this sucker work for now. I can always add ducts if necessary. Not the end of the world.
I'll make sure to get 80,000 next time(if I still live here). By then I should have new windows, etc, etc..


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Yea..I can't possibly imagine 60,000 being big enough - unless the home was super tight.
> I live in a 35 y/o home with original single pane windows. Insulation isn't bad(not perfect either)..but the windows are terrible. I'll get around to replacing them eventually..
> 
> 80,000 probaly would have been just fine.
> ...


Can always resize the orifices.


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## beenthere (Oct 11, 2008)

60,000, was just a number I used for example.

If the old furnace was 75,000BTU, and maintained temp.
Then increasing to a 100,000 is grossly oversized.

On your coldest days, did your old furnace have to run continuous, or did it cycle on and off.


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## Tommy2 (Nov 25, 2008)

beenthere said:


> 60,000, was just a number I used for example.
> 
> If the old furnace was 75,000BTU, and maintained temp.
> Then increasing to a 100,000 is grossly oversized.
> ...


Now that I recall..That old furnace would run pretty much continuously when it was single digits..

So a slight step up may not have hurt anything..But I'm not going to argue that 100,000 is probaly too large for my house. But I dont think Im off by too much.

Furnace still cycling fine today. Hmm. not sure what to think of it :huh:
Intermittent problems are the worst to solve..but, its working at the moment. So no complaints.

I still want to do the temp reading. Ill try to pick up a thermometor this weekend.


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Now that I recall..That old furnace would run pretty much continuously when it was single digits..
> 
> So a slight step up may not have hurt anything..But I'm not going to argue that 100,000 is probaly too large for my house. But I dont think Im off by too much.
> 
> ...



This 75kbtu furnace is the second furnace that's been installed since the house was new?


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## Tommy2 (Nov 25, 2008)

hvaclover said:


> This 75kbtu furnace is the second furnace that's been installed since the house was new?


Probaly. I have no idea on the house's history. Thats the furnace that was there when I moved in 2 years ago. It was from '02. 
I sold it..wanted to get rid of the oil stuff. Have an old oil tank. Hate the sootyness of it.


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Probaly. I have no idea on the house's history. Thats the furnace that was there when I moved in 2 years ago. It was from '02.
> I sold it..wanted to get rid of the oil stuff. Have an old oil tank. Hate the sootyness of it.


I think Beenthere was right about the size then.

Reason i say so is because back in the the 70s it was a common practice to oversize cause energy prices were so much cheaper and a bigger furnance was considered best.

When on the run the numbers at better insulation I come up with an 80kbtu.

i think the guys who did the oil furnace did a manual J calculation.


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## Tommy2 (Nov 25, 2008)

Just thought Id update that the furnace is still working fine.. 

I also did temp readings. I get about a 50* difference (60* cold, 110* )warm.

Still crossing my fingers, but looks like I might be in the clear!


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Just thought Id update that the furnace is still working fine..
> 
> I also did temp readings. I get about a 50* difference (60* cold, 110* )warm.
> 
> Still crossing my fingers, but looks like I might be in the clear!


Thats too dmaned low. Sure you are not tripping on high limit when you took readings?


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## beenthere (Oct 11, 2008)

My guess. Is those readings were taken at teh registers, and not the unit.


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## Tommy2 (Nov 25, 2008)

Right..So, I'm supposed to drill through the duct work on top of the furnace to take a reading?
Ive heard you're supposed to be several feet from the furnace. I was actually at the ducts closest to the furnace. (more or less right on top of it)

The rise range on the furnace is 45* to 75*

With the factory speed at medium high, it might make sense for it to be on the low end. 
I imagine that's good for the life of the heat exchanger atleast.


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## hvaclover (Oct 2, 2008)

I'm gonna bill you Dude...LOL

That model calls for the furnace to be run at least 15 minutes and the supply temp taken three feet from the plenum at the middle of the trunk.
This avoids radiant heat from giving false readings.

The return should be at the flex collar in the middle where it connects the trunk to the cold air drop.-


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## Tommy2 (Nov 25, 2008)

Well..Id have to drill through my sheet metal to do that. I think I'll just pass. Everything is working fine, and the readings I got were pretty close to the furnace - and not near the 75* limit to warrant further investigation. 
(i.e...the closer readings will probaly give it a 60-70* difference..still within the range)

I appreciate the help and will update if anything changes.


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> Well..Id have to drill through my sheet metal to do that. I think I'll just pass. Everything is working fine, and the readings I got were pretty close to the furnace - and not near the 75* limit to warrant further investigation.
> (i.e...the closer readings will probaly give it a 60-70* difference..still within the range)
> 
> I appreciate the help and will update if anything changes.



We drill holes in the metal all the time. No big deal. Just cover it with silicon when you finish.

If we were keeping track you'd owe us into four figures by now:laughing: So how generous HVAC guys are?


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## Tommy2 (Nov 25, 2008)

...Which is exactly why I did it myself :thumbup:
It's amazing how much it costs to have a contractor just walk through your door lol

Thanks again for the advice.


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> ...Which is exactly why I did it myself :thumbup:
> It's amazing how much it costs to have a contractor just walk through your door lol
> 
> Thanks again for the advice.



Oh stop acting like we come in with a ski mask and gun to give an estimate.:laughing:

You were fortunate you could handle the job. Why not post pics of what you did?


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## Tommy2 (Nov 25, 2008)

I have pictures..but no where to upload. Its really nothing special to see anyways. I'm fairly proud of the work, but I'm sure the pros do it better.
Hopefully Ill get a good 10+ years of service out of it. Particularly since Im more or less broke after buying all this stuff.

Filling the propane tank costs me $600  $2.63/gal. That puts me at about $3000 worth of spending in the last 6 weeks after new water heater, furnace, etc..

Ugh. I should have just went with wood or pellet lol


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## hvaclover (Oct 2, 2008)

Tommy2 said:


> I have pictures..but no where to upload. Its really nothing special to see anyways. I'm fairly proud of the work, but I'm sure the pros do it better.
> Hopefully Ill get a good 10+ years of service out of it. Particularly since Im more or less broke after buying all this stuff.
> 
> Filling the propane tank costs me $600  $2.63/gal. That puts me at about $3000 worth of spending in the last 6 weeks after new water heater, furnace, etc..
> ...


Don't forget to register the the furnace or you won't get the ten year warranty.
Have to do it on line or mail it in.


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