What burned my floor?

[Spencerwest]

Well we are currently redoing the rock around our stove which is a Whitfield advantage 2 insert. When I pulled the fake hearth stones up i saw this large burn spot underneath them right in the center. There is a mortar joint right in the center as well We bought this house a few years ago and it has always had the pellet stove. I can't imagine the pellet stove is putting out this much heat below it? It sits on a 5" pedestal on 1.5" fake hearth stones. The burn spot is directly beneath the burn pot area of the pellet stove.

Is it more likely that a log rolled out on the previous owner prior to the pellet stove and somehow an ember got through the mortar? More than anything I want to make sure it's safe to put the Whitfield back in. Thanks!

 

[begreen]

Maybe at some point in the past there was a wood stove there with inadequate hearth protection? Stone is not a good insulator, more of a conductor. Was there cementboard between the stone and the plywood? There should be.

 

[johneh]

We will never know how or why it burnt !!
What you need to know is how to protect it
so you do not have it happen again!!

 

[Spencerwest]

Exactly!! I'm concerned about putting it back the way it was. So what do I need to put between the subfloor and the pellet stove?

There was no cement board before so I assume that would be one thing I need to add. Is that enough of a fireproof insulator or does there need to be something else to prevent excess heat from transferring to the subfloor?

Interesting that stone is a conductor and not an insulator which now makes sense since you mentioned it. What is the correct way?

I know it's annoying to have a new guy ask a question that's been answered, so while I'm searching if you can point me to an article or post that'd be great, thanks!

 

[johneh]

See page 11 of this manual

https://woodburningdocuments.com/wp-content/uploads/2017/08/WhitfieldAdvantageII-T.pdf

Cement board is perfect Does not conduct heat cover it with stone, brick
or slate to make a hearth pad.
Others may chime in with other suitable material

 

[Spencerwest]

Thanks! I had literally just downloaded that after reading an article on here about hearths. It seems that is all I need and with several inches of air clearance, I should be safe. That is what they had before minus the board but according to the manual the stone is all that is necassary. So I would assume the burn happened prior to the pellet stove. Either way I will certainly install the cement board with rock on top and feel confident in that. Unless others have more to say, thank you very much for your help!

Ps. I think I will start a thread about cleaning the stove up while it is out. It hasn't seen any good maintenance in a long time. Here is a preview.