Class a chimney question...

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breckenridge

New Member
Oct 16, 2009
5
colorado mountains
I purchased a home built in 1984 with an existing wood stove and 8 inch class a chimney. I cleaned the chimney and replaced the stove with a new hearthstone shelburne which I have been heating with for three seasons. The original stove was a knockoff of a vermont castings defiant that was leaky, warped, and cracked leading me to suspect overfiring. The drywall and wood frame enclosure on the second floor was built larger than necessary with clearance from chimney to drywall of about 8 inches. For these reasons I decided to remove the enclosure , disassemble and inspect each chimney section, and rebuild the enclosure smaller to allow more space to pass in the room. After inspection all seemed fine with the chimney sections so I reassembled the chimney, and fired the stove up for inspection. I noticed the twist together union portions heated up faster than the rest of the pipe which makes sense. Also, the outside of the chimney pipe eventually got warmer than I expected even though with my hand held 2 inches from the pipe it was a comfortable temp.
The chimney was made by Oliver MacCleod..tested to UL 103 ht in jan of 1984..Projet model hi temp 3103. The original paper stickers are still in place and show no signs of heat.
I tend to be very cautious with fire and electricity , so my questions are..
Is it possible the slip joints getting hot first represents possible insulation settling and a possible hazard?
What should the outside surface temp be of class a chimney pipe at continuous operation?
Should I provide a larger clearance between chimney and drywall than 2 inches or even construct a simple sheet metal heat shield around the chimney for added safety?
Would durarock on the inside of the enclosure instead of drywall add any measure of safety?
Would replacing the entire chimney be a waste of time and $?
Am I concerned for no reason, since it has been used for years without any problems?
I live at 10,000 ft elevation and heat exclusively with wood if it makes a difference.
Thanks !
 
Is it possible the slip joints getting hot first represents possible insulation settling and a possible hazard? My guess is no.

What should the outside surface temp be of class a chimney pipe at continuous operation? Don't know...

Should I provide a larger clearance between chimney and drywall than 2 inches or even construct a simple sheet metal heat shield around the chimney for added safety? Sounds like overkill.

Would durarock on the inside of the enclosure instead of drywall add any measure of safety? Definitely. It couldn't hurt.

Would replacing the entire chimney be a waste of time and $? Probably yes.

Am I concerned for no reason, since it has been used for years without any problems? Probably yes.

I live at 10,000 ft elevation and heat exclusively with wood if it makes a difference. Not that I can see. Now, cake is another matter...

The opinions expressed here are not necessarily those of the management. Stay tuned; they'll chime in any moment now...

Nancy
 
What should the outside surface temp be of class a chimney pipe at continuous operation?
I would love to see any info members have on this one. The answer to that question probably answers most of the rest of the questions.
 
tfdchief said:
What should the outside surface temp be of class a chimney pipe at continuous operation?
I would love to see any info members have on this one. The answer to that question probably answers most of the rest of the questions.
Agreed. Anybody have any info on this? It will answer a ton of the initial questions...

I know that my class A which is outside stays cool to the touch when my flue temps are 400-500 degrees. Then again, when I touch it, the outside temps are usually -XX

Andrew
 
Mine in the attic is hot to the touch with the stove cruising. I will have to shoot it with my IR gun this winter and see what the temperature is.
 

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Breckenridge, I am like you. In our case, we kept access to the stainless when we built. Then we checked the thing under use to make sure I had assembled it correctly. In your case, it might be possible to install a temporary chase or a chase with a way to access the areas you are interested in. Then get an IR thermometer and some black spray paint and put a few spots on the stainless. Take the temps until you are satisfied. Jim
 
hey Jimbo - black spots on the pipe ? Just curious, does the IR therm not take accurate readings from the stainless? I am thinking of getting one for this season but didn't realize that might be the case ....
 
Thanks for the input everybody. I think I will wait till we get a really cold night (any day now at 10,000ft) and really get it cranking to see how it does before enclosing it. I will probably build in a small discreet acess panel for my own peace of mind also.
 
mikeyd said:
hey Jimbo - black spots on the pipe ? Just curious, does the IR therm not take accurate readings from the stainless? I am thinking of getting one for this season but didn't realize that might be the case ....

I think most IR thermometers are calibrated for emissivity coefficients of 0.8 or so. Most materials are in that ball park. Highly polished metals are about 0.1 or less.

Paint is in that 0.8 neighborhood. Polished stainless steel emissivity can be 0.075 or so. Perfect emissivity is 1.0. Other stainless can be up to 0.8, but those surfaces appear cast or sand blasted or weathered. So a paint spot on your stainless will result in a more accurate surface temperature reading if you are using an IR thermometer.

Here is a link with emissivities:

http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html

On that page is a link that has the net radiation heat loss equation.

My IR thermometer showed me I wasn't so smart after all. I found places in my house where heat was lost. The odd outlet here and there. One threshold on a door. And the big one was a zero clearance fireplace that had an air cooled chimney. If there was no fire, the chimney kept working keeping things cool. An energy waste for twenty years.
 
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