Block off Plate Construction!

[Fivehorizons88]

I’m planning on building a block off plate this fall to install where my damper used to be – I found some great instructions on how to build one on this forum – however, I would like some clarification on two things.


1: what kind of sheet metal should I use? Several people have used different types – is stainless steel my best option?


2: what is used to secure the Rockwool insulation to the topside of the block off plate so it does not move? Should I use a bit of furnace cement to adhere it to the metal plate so it does not shift?


Thank you so much!


Zach

 

[Nick Mystic]

There is no need to use stainless steel. Most people seem to use galvanized steel. You don't need anything too heavy or else it becomes more difficult to work with when you try to bend the outside edges to form a lip for attaching it to the fireplace walls. I don't think you need to secure the insulation since it is fairly stiff and won't move around. I just cut mine to fit and laid it on top of the plate before I raised it up into position. Good luck.

 

[webfish]

https://www.hearth.com/econtent/index.php/articles/making_a_block_off_plate/

 

[Jags]

Sheet aluminum is a very common material to build from.

 

[Fivehorizons88]

Sheet aluminum is a very common material to build from.

and these materials (galvanized metal and aluminum) are safe to use around high temperatures?

thank you!

 

[Owen1508]

Hey Jags/Webfish. question : I'd be weary using galvinized, although it should not heat up that much to give off fumes as a blocking plate. Is this a non issue.

 

[Owen1508]

and these materials (galvanized metal and aluminum) are safe to use around high temperatures?

thank you!

That's what I was thinking ...."Zinc Shakes" At low temps it is safe it just seems risky in my LR

 

[Jags]

Hey Jags/Webfish. question : I'd be weary using galvinized, although it should not heat up that much to give off fumes as a blocking plate. Is this a not issue.

If given the option - I agree, I would stay away from galv. material just as a precaution. The galv should never get to temps that will cause an issue, but why tempt fate. And depending on the method used to cut the material it could be possible for some material to go airborne. This could be mitigated by wearing a mask.

All in all - aluminum will be easier to work and it is readily available.

 

[Fivehorizons88]

If given the option - I agree, I would stay away from galv. material just as a precaution. The galv should never get to temps that will cause an issue, but why tempt fate. And depending on the method used to cut the material it could be possible for some material to go airborne. This could be mitigated by wearing a mask.

All in all - aluminum will be easier to work and it is readily available.

Alright - so it seems that aluminum is the "safest" material?

 

[Jags]

Alright - so it seems that aluminum is the "safest" material?

Yes. Probably overkill, but yes.

 

[begreen]

Here is another article on the topic. At the end are several links to threads of actual installations with pictures.
https://www.hearth.com/talk/wiki/why-damper-seal-is-needed/

 

[Jags]

And to the OP - if you notice, the instructions for building a block off plate DO state that galv metal is just fine to use. So use your best judgement.

 

[bholler]

we always use galvanized it shouldnt get hot enough to be an issue and if it did get that hot i would not use aluminum either it would degrade pretty quick at those temps.

 

[begreen]

I've read that the zinc coating will start to boil creating zinc oxide fumes at a little over 900F. Given the minimal point of contact and the wide heat sink effect of the whole block off plate this doesn't seem to be much of an issue, but I suppose the potential is there with a continually overfired stove or one that someone forgot to close the bypass on. Of course there are other issues with running a stove that way too.

 

[Fivehorizons88]

I've read that the zinc coating will start to boil creating zinc oxide fumes at a little over 900F. Given the minimal point of contact and the wide heat sink effect of the whole block off plate this doesn't seem to be much of an issue, but I suppose the potential is there with a continually overfired stove or one that someone forgot to close the bypass on. Of course there are other issues with running a stove that way too.

What do you mean by someone forgetting to close the bypass on?

thanks!

 

[Fivehorizons88]

I've read that the zinc coating will start to boil creating zinc oxide fumes at a little over 900F. Given the minimal point of contact and the wide heat sink effect of the whole block off plate this doesn't seem to be much of an issue, but I suppose the potential is there with a continually overfired stove or one that someone forgot to close the bypass on. Of course there are other issues with running a stove that way too.

nevermind - I looked it up. My Lopi 1250 actually does not have have a bypass rod.