Another safety question - how hot is too hot?

[BobUrban]

OK - I have looked up the chimney and feel I am burning good wood at an adaquate temp to limit creosote and that makes me happy. I am now wondering how hot the back wall can get?

The pics show my hearth I built. I have 1x slats screwed to the wall with 1/2" cement board screwed to them. I mortered 9x4x4 solid brick street pavers to the cement board. You can see my home brew make shift heat test I am using with 3 candles on the hearth and they barely melt at all. Actually the only one that shows any sign of melt is the center one right behind the stove pipe and that is just a little slipperyness inside the glass and not really melting. I was told by my TV people that if a candle does not melt sitting on or near my flat screen it will be ok. I have it hanging on the wall with another candle on top of it.

I just worry about the wall behind the hearth. I hung a meat theromometer probe I use in my smoker in the gap behind the brick hearth in a few locations and the hottest it got was 127 degrees. This is when I am running my stove steady at 350 and I will retest when I am running it hotter. Held directly to the painted drywall behind the stove pipe is only about 100-103 but behind the bricks is where I get concerned.

Anyone know if this is normal - hot - scary? no big deal?

 

[begreen]

You should be just fine Bob. That is a proper wall shield and then some. Too hot is steady heat over about 170F.

 

[soupy1957]

The area behind my wood stove surprised me............I expected extremely hot temps back there and yet, I found it to be quite reasonably moderate. I believe this is due to the design of the new EPA-rated stoves, with regard to how they are constructed. Using an older stove may reveal different results however.

I trust the manufacturers recommendations, the Installers know how, and the Town Inspector's knowledge of Code to put the stove where it should live.

That doesn't mean however, that I avoided any protection back there. When renovations were done, I made sure the Dry Wall behind the stove was the "fire retardant" type (thicker, if nothing else; although I suppose it may be chemically treated in some way, as well), and I had a mason come out and put up a layer of brick on the face of that Dry Wall, to live between the Dry Wall and the wood stove.

I maintain that we have less to worry about behind the stove, than we do elsewhere. No harm in protecting the back wall I suppose....."I" certainly took steps to ensure that......but "my" concern was that if the wood stove or flue should become compromised, there was less potential for fire development (or "it would take longer to develop") on the wall behind the stove, which is the closest object TO the stove.

I don't see any lack of protection behind your stove. If anything, I would be thinking about the stove's integrity itself. Is it older and showing signs of compromise? Should it be replaced? There does seem to be (from your pictures anyway) some evidence of age and overheating on the back of the stove. Maybe it's time for a newer stove??????

-Soupy1957

 

[BobUrban]

Thank you for the replies - that helps my peace of mind. Regarding the stove, yes, it is older and shows a little surface rust. It was siting in a garage for years and actually has very few working hours of use on/in it. The photo is an optical illusion as I have put a level on he back and there is no warpage. Because the stove was given to me and the chimney cost me 3000.00 to have installed I wanted to use it at least one season. I am planning to upgrade to a madern stove before next season and put this one in my garage(detached)

I will finanlize the decision after a year of burning and researching here to make a sound stove choice decision.

Thank you for the help

Bob Urban

 

[webbie]

What BG says!

Furthermore, the air could even be over the 170 - the actual surface of the drywall should be below that.

It would take years of exposure to temps well above 250 to really cause a danger...and actual combustion occurs at over 400-500+

 

[soupy1957]

".........and actual combustion occurs at over 400-500+ ."

I had heard that spontaneous combustion occurs at 750º????

-Soupy1957

 

[webbie]

Depends on how you define combustion. For our purposes, we don't want the wood charing and therefore lowering it's potential combustion point.25

These are C temps....but 120 degrees C is 250F.

For an extra margin of safety, somewhere about the temp of boiling water or of steam pipes in a regular radiation systems should be used as a guide - still 210-240 degrees F.

Of course, we also don't want common building materials and paints to break down...which is an entirely different subject! In general, keeping things below 150 total should take care of that.

 

[BobUrban]

Well I am no where near combustability no matter what it is now that I have this information. I also set a little fan blowing through the back of the stove from right to left. This helps circulate the air and keeps the wall about 100-105 in the dead air space behind the hearth. I am very comfortable with that and it is 75 degrees in here. I have never had my house above 65 unless I had company in the winter. This is just awesome!

 

[soupy1957]

The EcoFan I bought a number of years ago, (manufacturers premise is to blow the heat forward that would normally just rise vertically, which I don't entirely agree with in terms of how the heat radiates entirely), helps to pull the cool air from behind the stove.

-Soupy1957