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wood stove flue too hot? spikchik69 01-14-2007
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Posted by Edwin Pawlowski on January 14, 2007, 10:11 pm



>
> I should have specified the pipe temperatures in my original post. The
> thermometer I use shows the "best combustion" range as 300 - 475 F.
> Over 475 is labeled "too hot". When it gets up around 500, I shut 'er
> down to cool off a little.

Just let it burn down. That is not a big deal. As I said, I'd heat it up
every day to prevent creosote.

>
> The stovepipe is defintely single-walled - I have pulled it out of the
> chimney myself to look at it. It is probably not up to code.

Sure,it is. I've never seen multi-walled pipe in an exposed situation. You
want that heat in the house, not to force it up the chimney and waste it.
If you look at photos from many years ago, the stove would be in the center
of the old general store and a long pipe to the chimney to get the most heat
from it. Steel takes quite a bit of heat.



> And to clarify, it is the brick chimney that I am worried about, not
> the metal pipe. I have inadvertently let the metal pipe get red hot,
> so I'm pretty sure it can handle 500 F. I'm just not sure how hot the
> chimney itself is supposed to get. It is the chimney that gets too hot
> to touch. (I may have mis-used the word "flue" in my original post.)

Now that sounds too hot. I've never had my brick chiney so hot that I could
not lean against it easily. Right at the thimble it may be very hot, but
the mass of the chimney itself will usually absorb and diffuse the heat
safely. This is hte portion that is in touch withthe rest of the house,
like the framing.

> One friend tells me that the clay liner won't stand the heat of a wood
> stove, but another friend tells me that he has run his stove 24/7 for
> the past 3 weeks (he has a clay liner - ie, no metal insert).

Friend no. 1 is an idiot. Clay linings have been fired at much hotter
temperatures than your flue will normally see. What you don't want to do is
heat and cool rapidly, but they are made to take a LOT of heat.
http://www.sandkuhl.com/html/chimney_products.html
Clay Flue Liners

A flue liner moves smoke and gases, created by a fire's combustion
process, safely and efficiently from a home's fireplace. To do this
effectively over the life of a home, the flue liner must be able to
withstand excessive heat, chemical attack, thermal cycling and thermal
gradients. Sandkuhl Clay Works' flue liners easily endure temperatures in
excess of 1500°F. They are unaffected by the acids and other chemicals
created by the combustion process. Exposure to harsh outdoor conditions at
the top of a flue is no problem for Sandkuhl Clay Works' flue liners because
the materials are engineered for less than 2% water absorption. This
prevents spalling due to freeze-thaw cycles. Many materials cannot with
stand temperature differences between inner and outer surfaces (thermal
gradients) without failing. Ceramic flue liners are designed specifically
with this in mind.




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Posted by Harry K on January 14, 2007, 10:26 pm



Edwin Pawlowski wrote:
> >
> > I should have specified the pipe temperatures in my original post. The
> > thermometer I use shows the "best combustion" range as 300 - 475 F.
> > Over 475 is labeled "too hot". When it gets up around 500, I shut 'er
> > down to cool off a little.
>
> Just let it burn down. That is not a big deal. As I said, I'd heat it up
> every day to prevent creosote.
>
> >
> > The stovepipe is defintely single-walled - I have pulled it out of the
> > chimney myself to look at it. It is probably not up to code.
>
> Sure,it is. I've never seen multi-walled pipe in an exposed situation. You
> want that heat in the house, not to force it up the chimney and waste it.
> If you look at photos from many years ago, the stove would be in the center
> of the old general store and a long pipe to the chimney to get the most heat
> from it. Steel takes quite a bit of heat.
>
>
>
> > And to clarify, it is the brick chimney that I am worried about, not
> > the metal pipe. I have inadvertently let the metal pipe get red hot,
> > so I'm pretty sure it can handle 500 F. I'm just not sure how hot the
> > chimney itself is supposed to get. It is the chimney that gets too hot
> > to touch. (I may have mis-used the word "flue" in my original post.)
>
> Now that sounds too hot. I've never had my brick chiney so hot that I could
> not lean against it easily. Right at the thimble it may be very hot, but
> the mass of the chimney itself will usually absorb and diffuse the heat
> safely. This is hte portion that is in touch withthe rest of the house,
> like the framing.
>

Good post but...

A properly constructed masonry chimney will not touch any framing. At
least not in the few constuction manuals I have read. They specified a
2" clearance minimum. I don't know what code calls for.

Harry K


Posted by HeyBub on January 14, 2007, 10:48 pm


spikchik69@hotmail.com wrote:
> I have a wood stove in my basement. I have a thermometer on the pipe
> where it enters the chimney, and I keep it in the safe range.
>
> After about 5 hours of burning, the chimney / flue gets extremely hot
> about 12 inches over where the metal pipe goes in. It gets hot on all
> sides, not just the side where the pipe goes in.
>
> By "hot", I mean I can only hold my hand on it for a fraction of a
> second.
>
> I am pretty sure the chimney doesn't have a metal liner. I had a
> chimney sweep guy clean it out in the fall, and he didn't say anything
> about the liner not being up to the task of handling a wood stove. As
> I understand it, wood allows a lot more heat to go up the chimney than
> an oil furnace.
>
> The previous owner used the stove regularly (I just got the house in
> the summer).
>
> So I guess my question is whether or not it is normal for a chinmey to
> get this hot...?

Isn't it better that the heat goes into the room rather than up the chimney?



Posted by on January 15, 2007, 7:22 pm


Thanks everyone for the good information. I feel a lot better about my
stove now.

One more question...

In googling around the web for information on wood stoves, I read that
wood heat is notorious for sending excessive heat up the chimney.

Is there any sort of device available that you can insert into a
standard 7-inch stove pipe that will allow you to recover more heat
from the escaping exhaust? I would suspect that such an invention
would involve a fan. I can't seem to find anything like that on the
Internet.

Perhaps this has been tried but was found to restrict exhaust flow too
much?

Maybe a simple fan pointing directly at the pipe would be worth while.

Thanks all..
..sd


Posted by Goedjn on January 16, 2007, 1:52 pm


On 15 Jan 2007 16:22:37 -0800, spikchik69@hotmail.com wrote:

>Thanks everyone for the good information. I feel a lot better about my
>stove now.
>
>One more question...
>
>In googling around the web for information on wood stoves, I read that
>wood heat is notorious for sending excessive heat up the chimney.
>
>Is there any sort of device available that you can insert into a
>standard 7-inch stove pipe that will allow you to recover more heat
>from the escaping exhaust? I would suspect that such an invention
>would involve a fan. I can't seem to find anything like that on the
>Internet.


Fire-places are decorations, not heat sources, but a wood stove
should capture anywhere from 50% to 70% of the heat content
of the wood, without even trying. I've seen systems that
CLAIM up to 85%, but I'm not sure I trust that.

The most common way to extract more heat from a woodstove
is to put it as far away from the chimney-stack as possible,
and run pipe overhead between the two.

If you really want to go nuts, you could clamp/glue
an aluminium or steel fin the length of the pipe.
And painting it black might help, if it's not already.

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