Is my mantle getting too hot?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

ash bucket

New Member
Jul 6, 2009
57
central KY
I have a Fisher wood burning insert in my living room (it was already there when I bought the house). After the stove has been up to temp for a while I can put my hand on the bottom side of the mantle and it is almost to the point of being too hot to touch for very long. This worries me as I like to load up the stove and let it burn overnight while we sleep in the opposite end of the house. The mantle is custom made out of some old lumber. Not sure what kind of wood it is or how old it is. It is unfinished, rough looking, just the way I like it. I haven't measured it yet but the bottom of the mantle sets at least 24" above the top plate of the insert. The insert sets out of the fireplace opening roughly 10". Is there any possibility that it could get too hot and catch fire?
 

gzecc

Minister of Fire
Sep 24, 2008
4,829
NNJ
If its too hot to touch, something has to move. What are the specs for combustibles for that stove?
 

ash bucket

New Member
Jul 6, 2009
57
central KY
Not too hot to touch but much more and it would be. I was kinda hoping somebody could tell me what the specs are on it. I have found absolutely no info on Fisher stoves as I'm sure many people here know. I can't even find any pictures of my stove on the internet much less what the name of it is. All I know is it says Fisher in the bottom right corner of the right door. It has two glass doors.
 

jharkin

Minister of Fire
Oct 21, 2009
3,890
Holliston, MA USA
I looked it up and the auto ignition temperate for hardwood is approximately 570 F. Doubt your mantle is that hot if you can touch it :)


But as has been mentioned your best bet is to look up the clearances and adjust if necessary with heat shields/etc. Gives you a margin of safety in case of accidental overfire and covers your rear for insurance and code purposes.
 

ash bucket

New Member
Jul 6, 2009
57
central KY
Thought about a heat shield but I think it would be pretty unsightly. Maybe something I could install during the winter when I'm using the stove and take down during the off season. I wouldn't mind as much what it looked like so long as I could sleep better at night. Anybody have such a thing or know how I could make one?
 

savageactor7

Minister of Fire
Jan 25, 2008
3,751
CNY
Yes it's too hot...ya have to do something asap. When you play with fire you have to be right all the time...fire only has to be right once.
 
I've just been looking in to this kind of thing as it was pointed out to me on this thread that storing my logs close to the stove is potentially risky.

Please set me straight if I've got this wrong - If over time (whilst the heat is on) the wood does not char, blacken, then it will be OK. This can happen at temperatures as low as 80 o Celsius. If it does blacken it will be giving off combustable vapours that could ignite with a flame or spark. However in practice these small amounts of gasses would be blown away quickly. I would say, if you can at all times hold your hand on it, it will be OK.

Something else to look, I have a vauge recollection, could be borax as a fire retardent.

Andy
 

ash bucket

New Member
Jul 6, 2009
57
central KY
If I installed a heat shield, how much of a gap would I need between it and the bottom of the mantle. Would an inch suffice, or maybe a couple inches? I'm guessing the more the better.
 

ash bucket

New Member
Jul 6, 2009
57
central KY
I keep an eye on the underside of the mantle often and I see no sign of discoloring. Since this still does not ease my mind, I'm going to have to do something about this especially since savageactor7 put it the way he did. Just not worth the risk.
 
Before you do, just so you can get an idea of the real risk, try an experiment.

Hang some paper down from mantle, see how close to the stove top it needs to be before it chars and then ignites.
Of course don't leave it un-watched and have a bucket of water ready.

Have fun - and let us know how close you can get it.

If you have a straight up flue pipe the distance from this to inside of the mantle will be more important. UK regs state 18" for a 6" pipe.
 

begreen

Mooderator
Staff member
Nov 18, 2005
89,475
South Puget Sound, WA
jharkin said:
I looked it up and the auto ignition temperate for hardwood is approximately 570 F. Doubt your mantle is that hot if you can touch it :)

But as has been mentioned your best bet is to look up the clearances and adjust if necessary with heat shields/etc. Gives you a margin of safety in case of accidental overfire and covers your rear for insurance and code purposes.

As sustained heat breaks down the molecular bonds in the wood, pyrolysis can reduce the ignition point considerably.

ash bucket said:
I keep an eye on the underside of the mantle often and I see no sign of discoloring. Since this still does not ease my mind, I'm going to have to do something about this especially since savageactor7 put it the way he did. Just not worth the risk.

For peace of mind, hang a simple heat shield that is about 8" wider than the stove on the underside of the mantle. Attach using 1" non combustible spacers.
 

ash bucket

New Member
Jul 6, 2009
57
central KY
I'll have to do the experiment sometime when the wife isn't around because I don't even wanna hear what she would say about me playing like that. And the chances of me having a good fire going and her not being around are not good. Nice thought though.

About the flue pipe...is this something to worry about even though my flue pipe is in a masonry chimney?
 
ash bucket said:
About the flue pipe...is this something to worry about even though my flue pipe is in a masonry chimney?

Dont worry about that, the minium distance I quoted is air gap distance

I have the same problem wife problem with experiments as well, be sneaky hang bread up and pretend it's a new way of toasting. :cheese:
 

Bootlegger

New Member
When I replaced my old Fisher I installed a heat shield on our cherry mantle. In the pics below you'll notice that the cherry was charred from years of using the Fisher. The heat shield actually looks ok, not too obvious. And yes, you can take it down in the summer.

4127711227_9b545da0b4.jpg


4192884482_d5303f5b1c.jpg
 

ash bucket

New Member
Jul 6, 2009
57
central KY
Wow, that's crazy how charred your mantle is. Mine doesn't look like that yet. Although over years I'd say it would. I know for a fact that the previous owner of my house did not use my insert as much as I do now.
 

ash bucket

New Member
Jul 6, 2009
57
central KY
So I just found a heat shield for mantels on sale at northern tool for 24.99. Measuring tonight to see if it will fit and will be ordering if so! If not I will be making a custom one out of sheet metal from here at work. Thanks for all your replies. I will still be taking pictures tonight and posting them tomorrow just because I want to and to see what you guys think so check back in. Thanks again! Love this site!!!
 

heffergm

Member
Nov 24, 2009
162
South Shore, MA
You should contact the company to ask about clearances if they're still in business.

I had to remove my pine mantel. It had been there when I was a kid and my dad was burnig coal in a VC resolute, but when I put the new stove in it didn't meet the spec, which was something like 40". Not worth the risk for me. Code was different back in the 70s when the old stove went in. It didn't even have a liner, just a shorty pipe venting to the clay flue. Burned that thing for 10 years!
 

Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
BeGreen said:
As sustained heat breaks down the molecular bonds in the wood, pyrolysis can reduce the ignition point considerably.

Yes, and when it gets to the charcoal stage, it can auto-ignite at about 300ºF. That's pretty high still, but seeing that cherry mantle charred that bad, I'll certainly make sure that a heat shield is the first thing I install if I go ahead next year with that F 100 Nordic QT I've been eyeballing for my fireplace.

Interestingly, I use a pure charcoal block (made in my stove and cut into a block on my band saw) to silver solder on. I use an oxy-acetylene torch that is at about 5500ºF, and yet the charcoal never starts on fire. That's because the charcoal needs oxygen as well as heat to burn and the torch uses up all the oxygen. Pretty weird to see a red-hot block of charcoal sitting there on a fire brick when I know if I toss it into the stove it will disappear in no time.
 

Bootlegger

New Member
ash bucket said:
Wow, that's crazy how charred your mantle is. Mine doesn't look like that yet. Although over years I'd say it would. I know for a fact that the previous owner of my house did not use my insert as much as I do now.

I didn't even know it until I replaced the stove and I took that picture with a flash.
 

Cluttermagnet

Minister of Fire
Jun 23, 2008
937
Mid Atlantic
A mere 1 inch will do ya. That is an oft-quoted separation between various types of heat shields and combustibles such as walls, mantles, etc. Typically wood stove manufacturers specify that 1 inch separation. Amazingly, the heat shield usually allows you to decrease to 1/2 or even 1/3 of minimum separation without the shields.

I have a mantle heat shield, it works great! Does a fantastic job keeping it from getting warm. My mantle used to get pretty hot to the touch if the stove was really cranking (not all that often)- but not so hot I couldn't keep my hand on the underside constantly.
 

Cluttermagnet

Minister of Fire
Jun 23, 2008
937
Mid Atlantic
Bootlegger said:
Your mantle shield looks really good! This is the first photo I've seen of it. I did see the charred mantle in an earlier thread.
 

Cluttermagnet

Minister of Fire
Jun 23, 2008
937
Mid Atlantic
ash bucket said:
So I just found a heat shield for mantels on sale at northern tool for 24.99. Measuring tonight to see if it will fit and will be ordering if so! If not I will be making a custom one out of sheet metal from here at work. Thanks for all your replies. I will still be taking pictures tonight and posting them tomorrow just because I want to and to see what you guys think so check back in. Thanks again! Love this site!!!
Good deal. That should do ya. Make sure it contacts the wall or bricks that the mantle is hung on- no gap for stove heat to sneak behind. You'll be fine. 25 bucks sounds like a pretty good price for one.
 
Status
Not open for further replies.