Ok, you've convinced me to add a block off plate.....

.....after the initial posts, the forum convinced me to reverse direction........


I'm having a Regency I3100 installed soon. I have an external chimney that is 32' tall, and the existing masonry flue is 13"x13". The installer is using 6"flex pipe that will be wrapped in a flue blanket. In addition I want to have the installer place some insulation at the top of the flue around the blanket as an air barrier. What type (brand) of insulation should i use. I searched around here but could not see a recommendation for that. Thank you!

TheRambler said:

Typically it will be poured Vermiculite or Rock wool / roxul. You want a non combustible insulation for sure. This is also commonly in conjunction with a top and bottom block off plate.

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Rolux is available at Home Depot according to the Rolux website. That would be great! Thank you TheRambler. I too am in CT.

I don't think I'm going to do the block off plate. Going to put a blanket on the flue and put Rolex at the top to create an air barrier to the outside. I'm okay with losing a bit of heat.....I've run an open fireplace for twenty years so this will be a huge improvement.

.......I think there would only be a difference of a few percent in overall efficiency......what do you think the increase in efficiency would be?

tarzan said:

This is more of a question for the more knowledgable but wouldn't what the Rambler described be the best way?

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Yes, what Rambler described seems best.......I guess that I can install a block off plate after the installer does his thing. The installer is not doing a block off plate.....these guys want to get in and out. Perhaps I'll do it after. I'm just not sure how much of a gain there would be.

Even if I had it ready when they showed up I would not know where to cut the hole......

Grisu said:

There are plenty of people here that report a noticeable difference in heat output once putting a block-off plate in especially with an exterior chimney. Think about it that way: You have 32' of chimney where you send up air that is 100+ F and that is separated from the outside only by one or two layers of brick. That will be a substantial portion of your heat that goes into your yard.

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......so if you were me would you add this after the installer does his thing or try to work it in the day he is here......

Grisu said:

Insulation at the top will hardly be necessary if you have a damper-sealing block-off plate with some Roxul on top of it: https://www.hearth.com/talk/wiki/make-a-damper-sealing-block-off-plate/
Why heat the entire chimney and with it the outside when you can retain the warm air in your house?

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Thank you for the link......

Grisu said:

There are plenty of people here that report a noticeable difference in heat output once putting a block-off plate in especially with an exterior chimney. Think about it that way: You have 32' of chimney where you send up air that is 100+ F and that is separated from the outside only by one or two layers of brick. That will be a substantial portion of your heat that goes into your yard.

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.......so I think I'm going to try and do the block off plate.....first step it's to clean out the fire box.......I'll post progress.....Thanks for the encouragement.......

cableman said:

I just installed a friends and did the block off plate and insulated the sides and back of the fireplace with roxul, it puts out some nice heat right away. If i were you i would make the blockoff plate b4 hand and cut a hole bigger where you think it will sit. You should be able to get the measurments where the outlet on the stove will be. Make a cardboard templet of the top of the stove with the outlet hole.

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Thanks Cableman.....yes I'm going to make the plate, drill the holes, and precut the insulation into approximate chunks.

I know exactly where the hole should be. How much bigger would you cut it? Did you use silicone around the edge of the block off plate?

Ready to start the block off plate. Hope this is worth the extra effort.....