The Block-off plate from hell

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mstoelton

Feeling the Heat
Dec 16, 2013
486
SE michigan
So I began the weekend by picking up the material for my block-off plate from the local steel fab company. I have used them for several projects, always got top-notch service. I had sent them a drawing with measurements. I didn't measure the material since they always had been spot-on. That was my first mistake.

My second mistake was accepting the material when they told me they used 18 gauge steel instead of the 20 gauge they usually provide.

So I went home and proceeded to make the block-off plate presuming the material was cut to the correct dimensions - it wasn't. It was ~3 inches too long on the long side and correct on the short side. I found this out when I tried to dry fit the plate. I also found that the plate was about 1/2 inch wider that I specified.

So after a whole bunch of cussin' and such. I proceeded to trim the 18 gauge plate to the correct size. 18 gauge is a good bit thicker than 22 gauge (what I requested). It is much harder to bend, unbend, cut to size with tin snips, and re-bend. I also had to break out some of the smoke shelf in order to get the 6 inch stainless flue to come down the chimney in an acceptable location. I rented a small demo hammer from HD to do the breaking.

Long story short, I got the block-off plate installed with the 6" flue through it Saturday night at about 11:30 and called it a night.

Sunday mid-day we started the install for Clyde #2. That part went ahead fairly smoothly. We were able to lift up the flue, slide the Clydesdale into place and drop the flue into the top with little difficulty. I then finished out the surround and went up on the roof to add rauxal bats around the top of the chimney and finish out the top plate installation.

I let the furnace cement dry on the appliance connector and had a fire break-in fire going by about 8:00 last night.

I understand why many installers are unwilling to install a block-off plate. I spent more than a day getting mine installed on Clyde #2.
 
sounds like it was not fun at all....glad all got hooked up ok and is working. guess if there is a "next time" you'll measure before you take it out the door.
 
I know this won't help you since your installation is finished, but it could help someone reading this post who is contemplating a similar block off plate installation. When I did mine I made a full scale mock up with cardboard before attacking my sheet metal. The inside of most masonry fireplaces aren't built to close tolerances and it's difficult to just make a few measurements that will produce an accurate trapezoid (the shape of most block off plates). Once the cardboard template is trimmed to the exact size you can lay it out on the sheet metal and draw the correct shape with a magic marker. By cutting the finished block off plate about an inch long on all four sides you snip the corners and start bending the lip all around. Then when you put it into the fireplace if it's tight you can just extend your corner snips and bend the long sides a bit more. If it's short on any side you have the extra inch of metal you can use when you re-bend that side to make a better fit. The flanges all around also give you material to use to fasten the block off plate to your masonry work. I drilled holes in a few places and used screws to fasten it to my bricks.
 
I would not use heavier than 24 gauge for a blockoff plate. 26ga would suffice. 18 ga must have been a nightmare.
 
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