Why not use a small block-off plate on the damper opening?

Hello,

I'm about to install a direct vent gas insert into my existing masonry fireplace. I'll be doing a full reline for intake and exhaust. I've spoken to a lot of people about using a block-off plate, but everyone keeps saying no block-off plate is needed for a gas insert. Well after reading these forums, I am convinced I should use a block-off plate for efficiency, or at least some sort of insulation.

That said, why put the block-off plate a couple inches above the insert? Can I just remove the damper and then make a smaller block-off plate to cover the damper opening (since that opening is much smaller)? Then I can just lay some insulation on top of the plate and the old damper opening. I understand the damper is a little higher up, so the insert will be heating more air, but is it really going to make much difference?

Also, if the chimney is capped, will it make much of a difference if I don't use a block-off plate and just cram some insulation around the damper opening?

Thanks all, this forum has been so helpful!

Thanks, that makes sense. The plate seems like it would be the most effective, but time consuming to install. While I have everything open I want to make sure I do it right vice pulling everything out later on.

Thanks again!

You mean ceramic wool maybe with attached foil, like this?

http://www.efireplacestore.com/cpf-19124.html?productid=cpf-19124&channelid=FROOG

haha, very cool, thanks... I'll grab some mineral wool!

The install manuals for the gas inserts we install state to stuff the damper area with unfaced fiberglass insulation. Works good.

Our building inspector rejects anything with unfaced fiberglass insulation stuffed in like that - even though it doesn't burn (actually, it can, but at really high temps) it can melt down under the correct circumstances (or so he says.)

Our inspector is also the fire marshall - he sees a lot of the things that go wrong, and has seen some crazy stuff.

This stuff http://anvilfire.com/sales/pages/kaowool.htm is good though, and relatively cheap, and you can cut it to exact shape and fit it in the damper area. I used it on my wood stove install as a damper block off - works great!

whoah, that stuff looks pretty cool (2300F!) , thanks!

stuff the throat with Ceramic wool, much easier than a custom block-off plate!

stuff the top of the chimney around the vent and intake too

The guy that installed my DV gas stove put a block off plate just below the smoke shelf in my fireplace. He said that he liked to install them because it kept warm air from filling up the chimney and gave the install a cleaner look. He also said that I could pack the spaces not covered by the block off plate with insulation. I guess the whole thing could be insulation if thats the way you want to go.