Block off plate DIY

[Tsiskwa]

Firstly, thank you to those here who were helpful when we were looking at options for our fireplace. We ended up going with the VC Montpelier. We have been very happy with it so far, but I am now trying to maximize our heat output.

Unfortunately, our installer basically refused to do a block off plate, despite multiple inquiries on our part, and made it out to be prohibitively expensive. From what I’ve read here, I can’t see how or why that would be the case.

But in any case, I think it is a project I can at least attempt myself. I have attached a picture looking up the chimney (taken from the kitchen side of the previously double sided fireplace, which is still accessible without removing the stove). I have a few questions.

The things I have read here recommend Roxul insulation, and I picked some up today, but it says on the packaging that it needs 55cm of clearance to things like ducts and chimneys, etc...? Their website doesn't seem to reflect this, and in answer to a FAQ about stoves and ovens says "ROCKWOOL products have a high melting point of 2150°F and can operate at high temperatures. We do not currently have tested assemblies for these applications. The recommended commercial or industrial ROCKWOOL product will depend on the temperature and usage of the stove/oven. Please contact your local representative to find specific products."

Any recommendations on what type of material to use for the plate itself? Does it have to be steel? What gauge? Is aluminum an option? (I assume easier to cut to fit).

How tight should the plate be around the liner? Do I need to allow “wiggle room” for if the insert needs to be removed, etc?

Thank you, all!

 

[begreen]

Hopefully that is 55mm and not 55cm. If it is 55mm that is ~2.1" which is the mfg. instructions for a lot of chimney pipe. It is non-combustible and considered safe for packing around the liner. Don't pack it so tight as to greatly compress the batt or it will reduce the insulation efficiency. The plate is usually made from 26 ga steel but it could be made of aluminum. Maybe go up a size to 24 ga. in that case.

 

[Tsiskwa]

Gah! You are probably correct that it is mm, not cm. 26 ga seems thin enough that I should be able to work with it without much trouble. Should the opening fit tight around the stove liner, or does it need to have leeway? Thank you!

 

[begreen]

There needs to be a little gap around the liner so that it passes easily. Make the hole 6 1/4" for a 6" liner.
This wiki article may be helpful.

Make a damper sealing block-off plate

How to make a block-off plate A block-off plate is particularly helpful with inserts installed in fireplace on exterior walls with exterior chimneys. Without one, the flue liner (which should be insulated) and the stove will try to heat the mass of masonry that is exposed to the outdoors...

www.hearth.com

 

[maddog1016]

I used 23ga galvanized sheet metal. Just another option for you.. I never worked with sheet metal before, and it turned out great. Watch a few YouTube videos on sheet metal work without a sheet metal brake, and you'll be able to make a nice clean block off plate. Since your liner is installed and attached your best bet is making a 2 piece block off plate unless you plan on disconnecting it from the stove, but that seems like way more work than just planning for a 2 piece.

 

[Tsiskwa]

Yes, that’s the plan is for 2 pieces. I did the Roxul tonight. A couple smaller bits broke off and fell on the stove. I assume this is ok given their temp rating...? Also, would anyone mind looking at the attached picture before I proceed or light another fire? Just want to confirm I understood what to do correctly. Thanks!

 

[begreen]

That looks right.

 

[maddog1016]

Yes, that’s the plan is for 2 pieces. I did the Roxul tonight. A couple smaller bits broke off and fell on the stove. I assume this is ok given their temp rating...? Also, would anyone mind looking at the attached picture before I proceed or light another fire? Just want to confirm I understood what to do correctly. Thanks!

Few pieces on the stove top isn't a big deal; remove them for cleanliness if you desire. What you did looks good . Some people get away with stuffing with rockwool and don't even install a plate.. The plate is obviously preferred though to keep things in place.

Chances are you have quite a few batts left; if you have an exterior chimney it may be beneficial to insulate around the insert before installing the faceplate to keep the cold brick from absorbing more of the heat. Just don't block any of the air intakes or the insert jacket space.