# Is 190 degrees to hot of a surface temp for drywall



## lopiliberty (Apr 24, 2012)

Had the liberty cruising yesterday at 750 and flue temp of 400 and got out my new toy(IR Thermometer) and took the surface temp of the drywall right behind the stove pipe and the hottest place I could find was 190.  Stove is 11 inches from the wall, but the stove pipe is only 15 inches instead of 18 (single wall pipe by the way).  Been this way ever since the house was built 18 years ago and so far so good. Probably going to put heat sheild on it over the summer.  Just wanted to know if anyone thinks that is too hot for drywall.


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## pen (Apr 24, 2012)

That is about the maximum temp you'd want to see. However, since the stove is not installed to spec, that is an unacceptable situation.

I agree with adding a non-combustible heat shield w/ non-combustible 1 inch spacers which will allow air to circulate all around.

pen


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## lopiliberty (Apr 24, 2012)

yeah not sure why they didn't install the pipe 18 inches from the wall or why is was never caught.  Just to be clear it is 18 inches from the wall to back of the pipe and not the center of the pipe correct?


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## pen (Apr 24, 2012)

This manual http://www.lopistoves.com/TravisDocs/100-01164.pdf on page 8 says 18 1/4 inches, and on page 9 the pic shows it from the back of the pipe.  From what it looks in the pic, the back edge of the stove should be 15 inches from the wall for that to be the case.

Wonder if the installer misread where the 15 inches should be measured from.

pen


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## pen (Apr 24, 2012)

Also, depending on your setup if you wanted it looks like it would be acceptable for you to switch out the single wall for

AMERI-TEC model DCC with model HS chimney
DURAVENT model DVL with DURATEC or DURA-PLUS chimney
I.C.C. Excel (2100-2 Can.) (103-HT USA) chimney with HP connector
METALFAB model DW connector with TG chimney
SECURITY model DP connector with SECURITY model ASHT or S2100 chimney

and keep the stove in its current location.  Not sure if the a heat shield would serve as an eyesore or not.  The double wall pipe would be more attractive


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## lopiliberty (Apr 24, 2012)

The real question is WHO did the install of the dutchwest 18 years ago?


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## pen (Apr 24, 2012)

lopiliberty said:


> The real question is WHO did the install of the dutchwest 18 years ago?


 
That's what I said when I found my old fisher had this behind it. Just a little shy of the required clearances


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## BrotherBart (Apr 24, 2012)

The reference temp for the UL test is 190 degrees above the ambient temp. Ambient temp being the temp in the room. The drywall ain't gonna combust at that temp but the studs behind it are a pyrolysis fire just waiting to happen over time.


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## pen (Apr 24, 2012)

hmm, I was thinking 110 above ambient.

Regardless, it's installed less than the required distances

pen


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## lopiliberty (Apr 24, 2012)

No eyesore for me, could really care less.  Was going to go with double wall pipe but didn't.  Tried to save $$$.  Never thought but the old dutchwest could have had different code requirements and the stove pipe with the old stove didn't run anywhere even close to that temp.


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## BrotherBart (Apr 24, 2012)

pen said:


> hmm, I was thinking 110 above ambient.


 
Memory could be wrong. After a few years of blasting off Google on these questions ya start to go with what your old dead brain cells remember. 

Edit to add:

https://www.hearth.com/econtent/index.php/articles/stove_wall_clear


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## pen (Apr 24, 2012)

BrotherBart said:


> Memory could be wrong. After a few years of blasting off Google on these questions ya start to go with what your old dead brain cells remember.


 
I hear that.  I keep finding conflicting stuff, a page on hearth.com says 115 over ambient, but I found this also.  Not sure exactly what the wording means, but this is what it says:



> UL-127 Temperature limits on combustible surfaces are:
> 90F over ambient room temperature for unexposed (ie., in contact and covered) surfaces and 117F over ambient room temperatures for surface exposed to ambient air.


 
I don't understand what "in contact and covered" would mean.


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## BrotherBart (Apr 24, 2012)

My addled brain mixed up 90 over with 190 over. The 90 is a better reference. Best gauge is that if you can't hold your hand on it, it's too hot.


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## pen (Apr 24, 2012)

BrotherBart said:


> My addled brain mixed up 90 over with 190 over. The 90 is a better reference. Best gauge is that if you can't hold your hand on it, it's too hot.


 
I'll drink to that


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## webbie (Apr 25, 2012)

That's going to be too hot to touch, but still could be within safe range.

110 or 115 over ambient - and in a hot stove room, ambient is 80 = 190 or so. So that's the max.

Another way to think of this is that the hot water heat often goes through pipes and other stuff that is 190 degrees - and these often touch wood and combustibles. 

Still another way is boiler water - at 212 - would not be able to start a fire (even metal dipped in it)...but it would be way too hot for you to touch.

Personally, I don't like to run up against the 190-200 mark because it usually hurts the building materials themselves - that is, paint and wood. If it's a short time situation, that's another thing. The max temps do not take into account destroying your nice wood molding - just whether or not it will actually burn.


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## begreen (Apr 25, 2012)

That is too hot for my comfort. For peace of mind I would move the stove out the required 3" to meet spec. Overtime wood pyrolyzes and it's ignition temperature drops. You could be ok, but why take chances?


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## Backwoods Savage (Apr 25, 2012)

Should a fire ever happen, it is good to have things installed to code or better lest the insurance company fail to pay because it was not up to code. That should be enough of a motivator to get it right!


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## Mr_D (Jan 26, 2014)

lopiliberty said:


> Had the liberty cruising yesterday at 750 and flue temp of 400 and got out my new toy(IR Thermometer) and took the surface temp of the drywall right behind the stove pipe and the hottest place I could find was 190.  Stove is 11 inches from the wall, but the stove pipe is only 15 inches instead of 18 (single wall pipe by the way).  Been this way ever since the house was built 18 years ago and so far so good. Probably going to put heat sheild on it over the summer.  Just wanted to know if anyone thinks that is too hot for drywall.



Yes, 190°F is too hot for drywall.  

Due to having heat issues on my own fireplace I talked to Doug at the USG Drywall technical department.
He said as per the spec sheets on their web site the max continuous temperature exposure is 125°F max. for all USG drywall products including type X and type C drywall.  

I find it hard to belive that no one seems aware of this and installers all over the country routinely install drywall in area's that are too hot for it.  It won't burst into flame but it won't retain it's fire rating either after extended exposure to elevated temperatures.


PDF specs.
http://www.usg.com/content/dam/USG/...s-regular-firecode-cores-submittal-WB1473.pdf

The USG rep indicated that "temperatures over 125°F are not an appropriate use of this product" and such exposure will degrade the fire rating due to calcination (removal of water) of the gypsum.

Calcination renders drywall unable to properly withstand a fire event because the embedded water is already consumed ahead of time.  Calcination occurs as the embodied water of the gypsum material is driven off rendering the board mechanically and thermally unstable.  Strength decreases linearly with elevated temperatures and completed calcination is observed with temperatures as low as 125C.

see link
MECHANICAL PROPERTIES OF GYPSUM BOARDAT ELEVATED TEMPERATURES
http://www.fpl.fs.fed.us/documnts/pdf2003/crame03a.pdf

That document has a lot of detail such as:
Chemically combined water is expelled by the gypsum board between 100°C and 125°C, reducing the gypsum to plaster of paris with a loss of it's fire rating and structural strength.

Calcination is mostly complete after the gypsum board reaches a temperature of 125°C.  The initial high water content provides 90% of the fire-resistance of the panel.

Gypsum board contains approximately 21% water by weight and as calcination occurs the mass of the board is reduced.  
Structural Bending strength of drywall is reduced linearly starting at 100C to near zero percent remaining at 400°C temp exposure for 1 hour.

After 60 minutes of exposure at 200°C, the loss in modulus of elasticity in the gypsum matrix is essential complete (lost) with adhesion to the reinforcing glass fibers the only remaining component contributing to it's strength at that point.


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## tcassavaugh (Jan 26, 2014)

i'd find a sleeve or a couple of 45's and move it out, depending on how the install is. you'll sleep better at night, knowing its right.


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## NVHunter (Jan 26, 2014)

Would Durock Next Gen be a more suitable product to put behind a stove? The clearances would still be met. Or is there no difference?


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## Mr_D (Jan 27, 2014)

NVHunter said:


> Would Durock Next Gen be a more suitable product to put behind a stove? The clearances would still be met. Or is there no difference?


Good idea.    Yes, Durock can handle higher temps and is rated as a Noncombustible Material but there are some limitations.  The manufacturer rep at USG said Durock is rated up to 200°F when installed in a wall system.  That's not nearly what I expected considering it's a cement board product but apparently the limitation is because it has a fairly low R-value of *.*39 in 1/2" panels and *.*49 in 5/8" thickness.  The low R-value doesn't offer much thermal protection for whatever framing, insulation, or materials is behind it.  So the material it's protecting can get too hot in situations that have nearby heat sources.  Because of the low R-value it's supposed to be installed with a suitable backer board of some type.

On the plus side Durock won't burn in a fire situation but it also doesn't have the built-in protection and cooling effect (due to the embedded molecular water in gypsum) that Drywall has.   I didn't find a reference to a Durock max temperature limit of 200°F in any of the USG PDF docs I read but I presume the rep knows their own products.

There are many other insulation products that can handle far higher temperatures of 1000 - 2000°F or higher and some are structurally very strong, water resistant, rodent proof and posses other useful traits but selecting which one is optimal and practical is a long process.  Few people seem familiar with most of them and could say for sure which is the right one for the job.   For example there is:


High temp Ceramic boards and panels
Rock wool panels and batts

Fiberglass reinforced polymer panels
Foamglas from Pittsburgh Corning that comes in many shapes and sizes.
IIG Thermo-12 gold panels are strong and rated for 1200°F and looks promising.   

Any of these products will take more research to determine what is the optimal product for residential wood stove applications.   
I'm hoping the experts will chime in as I have a similar issue to figure out as well.  My RSF Focus 320 wood fireplace can heat up the insulated chase walls to 210°F in 1 -2 hours at which point I shut it down as I know that's already too hot and it was still going up.  I ran some detailed experiments on that but I'll publish that info over on the thread I started for that a while back .


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## NVHunter (Jan 27, 2014)

What thread did you start regarding a chase?  My install has to have a chase due to HOA requirements and I've been wondering how to keep the chase from getting too hot. 210 in the chase is high it seems. 

How do you keep the chase cooler to avoid too high of temps?


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## Mr_D (Jan 27, 2014)

NVHunter.. the thread with my chase project and issue is at 
https://www.hearth.com/talk/threads...d-fireplace-gets-too-hot.119667/#post-1601795

Until we figure out the best solution, I keep the chase cooler using automatic digital temperature controllers.
One turns the internal (optional) blower on high anytime the flue gets up to 550F.  Another turns on the basement heat dump blower at 600F or above if further cooling is needed.  Both fans allow good fire temps but don't allow it to overfire either by drawing off excess heat back into the room.  The fans do a good job of cooling down the firebox and flue by 100F or more as needed and this cools the chase by about 50F.  

The fans on auto sound like a quiet furnace going on and off at regular intervals to keep the chase cool and it heats the room more as needed.
I set the temperature span to 20F so they don't cycle off/on too often.  Everything is adjustable.

It's actually a really nice feature having adjustable, automatic, thermostatically controlled fans vs open loop temp with no control.  
You set the temperature you want to burn at and it holds it pretty tight into that range such as 525 - 575F as long as you add wood sometimes. 

It maintains a good temperature for clean burns, limits the max temp, and extends the burn time by turning the fans down as the firebox cools.  The original factory bimetallic air damper still works as intended too but that can only adjust the air flow and not very much apparently.  The fans are more effective.

After the chase design is adjusted I shouldn't need the extra temp controls.  We'll see.


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