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wood stove flue too hot?



 
 
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  #1  
Old January 14th 07, 10:30 PM posted to alt.home.repair
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Posts: 3
Default wood stove flue too hot?

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...?

Thanks..

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  #2  
Old January 14th 07, 11:33 PM posted to alt.home.repair
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Posts: 252
Default wood stove flue too hot?

wrote in message
oups.com...

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.


Omissions:
1. Since you have a stovepipe thermometer, we can
advise better if we know what it indicates. Hot to the
touch is not an adequately precise indicator.
2. You should be aware that, in some jurisdictions
(e.g. Ontario, Canada) the fire code is retroactive, i.e.
you may be required to upgrade to comply with the
current code (more probably by your insurance
carrier than by local government.)
3. Modern stove flues ought to be double-walled
(as modern fire codes are likely to specify.) These
are tested by the standards authority to withstand
interior (smoke temperatures) as high as 2000 Fahr.
(Some firemen recommend an intentional chimney
fire every year or so for cleaning purposes: but they
are probably not supposed to say this.) Books
about woodstove efficiency recommend the
temperature inside the smokestack ought to be
above 300 Fahr. -- no problem in a double flue.

You can see for yourself whether the pipe is single-
or double-walled by disassembling the stove pipe.
If uncertain about this, have the chimney sweep
show you how on his next visit.

Do not ask your insurance carrier or agent for
advice about wood stove safety. You are not likely
to get a coherent answer and you may put the
insurer on the road to cancelling your insurance.
But it is in your own interest to find out what your
local fire code specifies and conform to it if you can.

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)


  #3  
Old January 15th 07, 12:49 AM posted to alt.home.repair
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Posts: 5,834
Default wood stove flue too hot?


wrote in message
oups.com...
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.

So I guess my question is whether or not it is normal for a chinmey to
get this hot...?


What do you consider safe range? I usually run my stove so the cast iron
top is at least 400 degrees, and a couple of times a day, run it up to about
700F to keep it clean. The stove pipe is easily 400 at any given time.
That, IMO, is normal. What does your actually read on the thermometer?


  #4  
Old January 15th 07, 01:25 AM posted to alt.home.repair
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Posts: 3
Default wood stove flue too hot?

Thanks for the speedy replies.

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.

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. I am
having a new wood furnace add-on attached to my oil furnace next year,
but would like to get through the winter with this stove. But I don't
want to crack or otherwise ruin my chimney or burn the house down in
the mean time.

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.)
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).

Thanks again, I appreciate the help..
Stephanie D.

  #5  
Old January 15th 07, 02:08 AM posted to alt.home.repair
EXT
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Posts: 1,649
Default wood stove flue too hot?

If you are meaning the brick chimney with a vitrified clay liner is getting
warm on the outside after several hours, I would consider that normal. The
tile liner/brick exterior are masonry units in contact with each other. Heat
will eventually start to transfer, in certain masonry stoves this is
considered a heat sink to hold the heat for future release.

The pipe between the stove and the chimney is normally single wall as it is
supposed to be an additional source of heat. The chimney should be either
masonry with a clay liner, or a masonry with a stainless steel liner, or a
class "A" double wall insulated metal chimney. While masonry chimneys have a
problem, especially if they are on an outside wall, of having a lot of
creosote and moisture until they slowly heat up, they are very durable.
After all the clay liner is kiln baked and heavily glazed with kiln baked
coating. Anything your wood stove will do will be less than it survived
during manufacture.


wrote in message
ps.com...
Thanks for the speedy replies.

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.

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. I am
having a new wood furnace add-on attached to my oil furnace next year,
but would like to get through the winter with this stove. But I don't
want to crack or otherwise ruin my chimney or burn the house down in
the mean time.

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.)
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).

Thanks again, I appreciate the help..
Stephanie D.



  #6  
Old January 15th 07, 04:11 AM posted to alt.home.repair
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Posts: 5,834
Default wood stove flue too hot?


wrote in message

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 1500F. 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.



  #7  
Old January 15th 07, 04:26 AM posted to alt.home.repair
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Posts: 3,053
Default wood stove flue too hot?


Edwin Pawlowski wrote:
wrote in message

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

  #9  
Old January 16th 07, 01:22 AM posted to alt.home.repair
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Posts: 3
Default wood stove flue too hot?

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

 




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