Idea for making custom reflector for fireplace opening behind free-standing woodstove

[sksmass]

I have a Fireview that is free-standing in a room that exhausts through a fireplace behind it. All of the clearances are fine. I'm quite happy with it. However, I notice that the fireplace brick behind the stove gets warm (not hot) after awhile and I can't help but think about how much heat is being transferred to the masonry instead of being transmitted out to the living space of the room.

I like to squeeze every BTU out of my wood. So, I am thinking about designing a bent reflector, that fits the contours of the fireplace box, to reflect the infrared back out into the room. I'm thinking about using "specular aluminum lighting sheet" (that mirror-like sheet metal used as a reflector in some florescent light fixtures). Or. alternatively, I could bend/crease a piece of 1" ductboard (R-value 6.5) to fit the opening. Ductboard is essentially thin fiberglass with a foil skin on it.

Pictures of the fireplace opening and a diagram of the plan attached below:

Two questions for the forum (comment on both!):
1) dumb idea? Like, am I being too compulsive and I should just let it go?
2) which option do you like better, the aluminum sheet idea or the ductboard idea? I KNOW aluminum sheet is non-combustible. I'm not so sure about ductboard. Its MSDS (linked above) says it has a "smoke development index of 50 (whatever that means).

 

[Grisu]

Regarding 1) Where do you think the heat is going after it transferred to the masonry? Is the fireplace at an exterior wall?

 

[begreen]

It's mostly a question of aesthetics. A couple questions about the installation. Is there a block-off plate a the damper level? Is that smokepipe going up the chimney or does it connect to a stainless steel liner right above where we can see in the picture?

 

[sksmass]

Good questions.
It is an internal (central) chimney so, its true, most of the heat does stay in the structure. But it just doesn't seem like usable heat. A lot of it is "spent" heating up internal framing members and drywall in closets.
There IS a steel blockoff plate at the damper level and there IS an insulated liner all the way to the top. Part of this project will be to put a layer of Roxul on top of the block off plate.

 

[begreen]

If it's a full interior chimney the mass of masonry, walls, framing etc. release the heat slowly back into the house as the fire cools down. If the house cools down rapidly as the fire dies down it could be a heat loss issue elsewhere in the house. For the stove setup, it sounds like you have already done some good steps

 

[Grisu]

It is an internal (central) chimney so most of the does stay in the structure. But it just doesn't seem like usable heat. A lot of it is "spent" heating up internal framing members and drywall in closets.

With an internal fireplace I would not worry about it. The heat is not "spent" as in "lost". The masonry etc. will warm up and then slowly release it back into the house again until air and structure have equal temps. With your plan you may feel a bit warmer in the stove room but that heat will have been subtracted from the other adjacent rooms.

The Roxul on the block-off plate makes sense, though.

 

[velvetfoot]

Then too, if you stand at the focal point you might be barbecued.

 

[begreen]

Headlines: Man spontaneously combusts in front of stove

 

[kennyp2339]

Headlines: Man spontaneously combusts in front of stove

That happened to my dad two Christmas's ago, he sat in front of his insert and was telling us a story about growing up and being poor (sharing toys with his brother, like they could get (1) truck and split it in half stuff) and while he was deeply immersed in his story my sister and I started laughing because there was whisps of smoke coming off the back of his sweatshirt. I was really funny and a good memory to have.

 

[branchburner]

I agree with others that with an interior chimney, if heat is not being allowed up the flue, the masonry is simply an extension of all the other mass in your house (walls, floors, furniture, etc.) that absorbs and holds heat, so it is not really "lost". But I see your point that a portion of that heat is not useful (my re-radiated masonry heat keeps a neighboring closet VERY warm).

I did put two metal sheets in my fireplace to reflect heat out, because 1) my stove has a rear burn chamber that throws a lot of heat out of the back, and 2) my stove is recessed part way into the fireplace. Neither of these apply to your setup... your stove appears well out into the room.

For my money, any gain you might realize would be offset by the negative impact of a less appealing appearance, as the existing brick will be more attractive than the shiny reflecting material to most eyes.

One thing essential to my setup is a fan on the floor that blows cool floor air to the back wall of my fireplace. This acts as my "blower" and not only pulls heat off the very hot rear chamber of the stove, but off the fairly warm masonry, as well. For me, this is far more important than re-directing radiant heat, as force-moving the cool floor air feeds and improves the natural convection currents.