Copper sheet for hearth pad and heat shield

[Morso1bo]

Hello,
I am installing a new morso 2b standard in a small cabin and am wondering if I could use a copper sheet to protect the pine floor and wooden walls, if I follow the manufacturers clearances. I usually use stove boards under my stoves but we are always tripping on them. I know I will need an air gap behind the wall heat shield If this would work how thick should the sheets be? Thanks so much for any advice!

 

[EatenByLimestone]

You can, copper is so soft it might not protect the pine much from denting. I have a piece of steel sheet metal under mine. I don’t think it’s dented by the stove. Maybe it is under the legs and I just can’t see it.

 

[Morso1bo]

Thanks so much for your input. I hadn’t thought about all the denting from the stove and dropped logs! Good to know that it would protect the floor. Seems like it just needs ember protection.

 

[EatenByLimestone]

I think that’s all code is worried about. Copper would certainly provide ember protection.

 

[Pinesmoke]

From a perspective of thermal conductivity copper is very high compared to steel. Using it as a heat shield would be stunning in appearance but would move a lot of heat through it to the air gap.

I solder a lot of copper wiring and it crossed my mind how quickly it gets too hot to handle.


https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html

In round numbers it's 5-6 times more conductive than carbon steel.

 

[stoveliker]

I don't think the difference in the quantity of heat moved will be that significant, given that the plates are thin. It'll move quicker (i.e. the temperature gradient across the thickness will have set up more quickly) through copper, but the end result for a stove that burns many hours will be similar I think (given that the pine floor does not move the heat away very quickly, meaning that the temperature at the bottom of the plate will be the same, leading to the same temperature gradient across the plates for both metals) - though I might be wrong in that.

More importantly, infrared radiation is likely to be the majority of the heat load on the plate. IR absorption of copper is far, far less than steel (and that's shiny steel, not stove-paint black, which would. even be worse). In other words, copper reflects more IR than steel.

I don't know how copper would (in humid summers) oxidize? (become greenish)

 

[bigealta]

The copper won't oxide to green unless subjected to certain fluids. I make copper weathervanes and after 20 plus years on the ocean on Block Island, there is no green yet on my weathervanes. The Only green spots that develop are where the flux from soldering was not completely cleaned off. Greening of copper takes forever.

Outdoor copper will brown. If you want it to stay bright copper color spray it with a clear coat.

 

[bigealta]

1/8" 3'x8' is $3,400 at metal depot.

3/16" (a36 steel) 2'x8' is $184.

 

[Morso1bo]

Thanks so much for the input everyone!

 

[EatenByLimestone]

I picked up the steel sheet metal under my stove at a plumbing supply house. I’m not sure what alloy it is. It was 3x5, maybe $30. I doubt it’s double that now.

 

[MongoMongoson]

The proper thickness of a metal wall heat shield is a minimum of 24 gauge. NFPA 211 does not specify a metal. It just says "sheet metal" so you can use whichever metal you prefer.

I thought using copper would be the most attractive, by letting it brown naturally over time. I don't know where to source it, so we ended up with bright galvanized steel. My wife likes the look well enough that when we switched to a modern stove with closer clearances, she wanted to leave the heat shield installed... and that is what we did.

10-series 80/20 aluminum extrusion makes a very convenient non-combusible 1" wall spacer. I was able to source free scrap chunks of 15-series (1.5") 80/20 so I used that instead.

If you Google NFPA 211 you can find an older PDF posted which describes the requirements in detail.

 

[Morso1bo]

Thanks so much for your reply. I think the price of copper is going to make the decision easy for me! Sheet metal is looking pretty good to me.

 

[Morso1bo]

I found this used heat shield online and am wondering if it would be adequate protection. I will attach pictures of stove in general position with dimensions. Also picture of heat shield which is 32”x32”. Thanks again for all the help!

 

[stoveliker]

That depends on the material (I think it's fine) and on the size (what does your manual say?).

 

[Morso1bo]

The stove manual only mentions distance to combustibles. Here are stove dimensions.

 

[stoveliker]

Page 12 tells you how large it should be.

 

[Morso1bo]

The stove is almost 24” long not including ash lip.

 

[stoveliker]

The pad should at minimum be 40" long (front to back, with 16" in front). and 25" wide (6" in each side).

I note that the table says 6" to the sides, the text says 8" to the side. The latter is in the table only for Canada. So it's not clear to me what the US should be. Better safe than sorry, I'd say.

 

[stoveliker]

 

[stoveliker]

So, what you found at 32"x32" is too small in length, even if it would suffice in width.

 

[Morso1bo]

Thanks! Should the wall protection Mach the floor protection length?

 

[stoveliker]

If you adhere to the clearances to combustibles as listed on page 11 - as you should- then there is no need for wall protection.

 

[stoveliker]

Note that in some cases one can decrease the side and back clearances by adding a vented shielding.
But I believe that should be mentioned in the manual as allowed.
It is not as far as I can see. Hence you can't decrease clearances by adding a shield.

You can still add a shield if you wish for additional safety and/or aesthetics, but the original clearances should be adhered to as on page 11.

 

[Morso1bo]

Thanks for your input. I want the installation to be safe for sure.