# Temperature of vent pipe before it exits through the thimble



## northernweather (Oct 29, 2012)

I have a temp of approx 80c on the outer lining of my exhaust just before it enters the thimble. What are the temps others are experiencing? I contacted selkirk a few minutes ago and they had no clue what is acceptable for their type L vents.


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## mepellet (Oct 29, 2012)

Depends on what the outdoor temp is.  Mine is usually pretty cold right at the thimble.  Always colder than room temp at least.....


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## Harvey Schneider (Oct 29, 2012)

I measured 120F (49C) on my Duravent with my 25-PDVC running at a setting of 5 for 1/2 hour. The front of the stove was at 375F (190C) at the time so I assume the exhaust gases were at least that hot.


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## SmokeyTheBear (Oct 29, 2012)

Here is something from a pellet stove technical manual which should give you some idea about the variability depending upon firing rate and fuel, please note that the low firing rate range includes temperatures below what I would want to be running at.  The exterior vent temperatures will vary accordingly.


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## slls (Oct 29, 2012)

My pipe to wall is 12 inches, I can hold my hand on the center and leave it there on med heat.


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## northernweather (Oct 29, 2012)

I am not sure what the difference is here then. Is everyone else running insulated vent pipe? My selkirk pellet stove vent pipe is not insulated, only double walled with an airspace between tubes. I am using my mag thermometer from my woodstove pipes to "guesstimate" the temp. Not an exact temp but i was just looking for a ballpark figure. I just realized on the thread title i wrote before it exits. I am looking for normal temps inside the house, just as in enters the thimble. Sorry if I confused anyone, do it to myself constantly!


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## SmokeyTheBear (Oct 29, 2012)

That air gap is in fact insulation as it creates a dead air space between the pipes.

The temperature on the outside should vary along its length as it leaves the stove. 

The test that is performed is for the temperature the combustible material sees at the minimum clearance to the vent and not what the vent itself is.  The clearance distance depends upon the venting, some venting is only tested to 3" and some to 1".


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## northernweather (Oct 29, 2012)

Thanks Smokey, I am not overly concerned about the temp. I can hold my hand 1/4 inch away from pipe and not feel any heat radiating, but it is too hot to keep my hand on it where it goes thru the thimble. Outside of thimble is also wrapped in insulation. (not inside between thimble and vent pipe) I got a little unnerved because im used to my selkirk for woodstove that I could lick if I felt so inclined. Thanks to all for their tips, info and sharing of knowledge. I will get the hang of this yet!


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## Heatsource (Oct 30, 2012)

L vent is rated for 450*f (inner liner) continuous iirc


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## subsailor (Oct 30, 2012)

A1Stoves.com said:


> L vent is rated for 450*f (inner liner) continuous iirc


 
Hey Dave,

If you're a Harman dealer, at least spell it right in your sig!


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## Ironhorse74 (Oct 30, 2012)

If my memory serves me right Type L is rated for 570 degrees continuous. B-vent for gas appliances is rated at 450 degrees continuous.

But I am old.... and it has been a lot of years since I had to pass a mechanical license

Brad


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## northernweather (Oct 30, 2012)

Thanks again folks. I realize that the air gap does insulate to some degree, but i was wondering what surface temps that everyone experience on entry to the thimble. Here's hoping all is well with the folks hunkering down through the storm.


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## jjs777_fzr (Oct 31, 2012)

Harvey Schneider said:


> I measured 120F (49C) on my Duravent with my 25-PDVC running at a setting of 5 for 1/2 hour. The front of the stove was at 375F (190C) at the time so I assume the exhaust gases were at least that hot.


 
I'm running a 25-PDVC at heat/blower setting 1/1 using Simpson Duravent.  It goes up about 5 feet then 90 to the outside thru thimble.
To measure I'm using the Centech IR gun (for accuracy I've tested on a pot of boiling water - and it is dead on).
Using ACP pellets I was measuring about 120-130F consistently at the top elbow before it exits thru thimble.
I emptied the hopper and filled with Dry Creek pellets.
Temps were consistently 151-155F.

Note - ACP pellets as tested by JT versus DryCreek are notably one of the lower performing pellets that I've seen tested - but I'm cost conscious and if it burns I use it.  20 degrees or 1 shovel more ash doesnt mean that much to me - but I was impressed at JT's testing and it chimes nicely with the differences I saw at the stack.  What does all this mean ?  I dunno but I find myself shooting the IR gun at everything and I like it.


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## tjnamtiw (Oct 31, 2012)

jjs777_fzr said:


> I'm running a 25-PDVC at heat/blower setting 1/1 using Simpson Duravent. It goes up about 5 feet then 90 to the outside thru thimble.
> To measure I'm using the Centech IR gun (for accuracy I've tested on a pot of boiling water - and it is dead on).
> Using ACP pellets I was measuring about 120-130F consistently at the top elbow before it exits thru thimble.
> I emptied the hopper and filled with Dry Creek pellets.
> ...


Remember that IR guns will give you different readings depending on the surface color and texture of what you are measuring.  A stainless pot versus a black stovepipe.....
It's really hard to tell what the differences in stack temperature mean other than more heat was being lost up the stack with the Dry Creek pellets.  Perhaps they were smaller pellets which means more were being fed into the burn pot, hence more heat was generated overall, with resulting extra heat going up the stack.  Conversely, maybe fewer ACP pellets were being fed resulting in a smaller fire.  There are so many variables and without being able to scientifically weigh both batches, it's just a guessing game.  Some people will swear that a particular brand is better (hotter) when all they really are doing is feeding more pellets because they are cut smaller.  For me a good versus bad pellet is how much ash I get and are the pellets too darn long to even feed.


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