Combo Furnace, chimney not heating up enough


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Old 01-07-07, 07:00 PM
R
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Combo Furnace, chimney not heating up enough

I have a oil/wood combination furnace and having a hard time getting the chimney up to proper temp. when burning wood. The furnace is a 1979 NewMac CL-170G oil/wood combination, similar to: http://www.newmacfurnaces.com/showroom/cl86g.html only alot older.

It heats up the house really well, but the flue thermostat only gets to 200 when I'm really trying to get the fire burning, even with the bottom cleanout door open to get a really good draft. And normal operating is at about 100-150. I can get the house really cooking at 80-85 deg. and the flue temp still sits at 150 deg. I know normal temp to prevent creosote deposits is 300 - 600, and the manufacture recommends heating up the chimney to 600 once a day and then burning at 300-500.

I had it up to 500 once when I first used the furnace, but that was with some really old/seasoned wood that the previous owner left in the cellar. But the house got up to 89 deg also. I am using seasoned wood. I just checked and cleaned the chimney and flue pipe and it did have some buildup of creosote.

Any Ideas on how to get the flue gases hotter?
 
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Old 01-07-07, 07:32 PM
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Off the cuff I am unsure what your problem is but can you answer these questions:
Where did you measure the temperature?
Is there a chance your temperature measurements are in Celcius?
Could your thermometer be way out of whack? Think about it. If the temperature were ever around 100 degF you would be able to lay your hand on the flue pipe almost indefinately and 150 deg is around the temp of hot tap water.
Some creosote build-up is almost unavoidable on this type of furnace especially if you have a temperature operated damper.
Was the build-up quite excessive?
 
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Old 01-07-07, 07:54 PM
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Thanks for the quick response:

1) Temp has been measured on flue pipe at both, at furnace and chimney. Both are same (approx.) temp.
5) Nope definitely F
2) Didn't think about thermometer being messed up, is new, but that doesn't mean much. Just checked and its sitting at 100, could lay my hand on the pipe but only for a second.
3) Don't know if it matters, but the forced draft fan is missing on front. I don't see that as a problem because it would only run when the house is calling for heat, which its always warm enough that it doesn't.
4) There was only a thin layer of creosote, no thick build-ups.

Thanks again, and I'll get another thermometer to check. The manufacture recommends a probe style, couldn't find any locally so I just got one of the magnetic types. Are they really that better, think its worth ordering online?
 

Last edited by rjels; 01-07-07 at 07:55 PM. Reason: add 5)
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Old 01-07-07, 08:19 PM
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There really isn't a lot that you can do.
The flue temperature is quite dependant on the firing rate of the stove.
If it happens to be oversized for the space then you have few options.
Your situation is similar to mine.
I have a wood/electric combination and find that once the house comes up to temperature the automatic damper chokes off the fire.
I have had very good success with creosote removing chemicals.
It is a powder you throw on a fire and it causes the creosote to not stick.
At the end of the first season I used the chemical the cleanout had a good pile at the bottom and I didn't need to brush it.
 
 

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