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Insulation in furnance/hot water tank room - options?

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Deal Addict
Nov 2, 2011
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Insulation in furnance/hot water tank room - options?

I am finishing my basement which was completely gutted, the exterior wall framing is done, and recently had it all spray foamed.
For the furnace/hot water tank area, I was advised they wouldn't do it in there because of a fire hazard.

My issue is, the area the hot water tank and furnace are in is quite limited for space, so the spray foam was really the only option to insulate the walls. It is a small house, and the furnace and hot water tank are located in one corner of the basement side by side. I could possibly cut and slide some rigid foam board insulation in there, but it would still be tight. There would not be enough room behind the water heater for example, to then install studs for drywall, etc. over top of the foam board.

It just seems weird to insulate and finish the majority of the basement, to then leave the furnace area exposed with concrete block walls.

Anyone have a small furnace room and what did you do to insulate it, if anything? Or if space is an issue is it normal to just leave this area exposed?
13 replies
Jr. Member
May 12, 2021
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Yeah you should insulate as you may have condensation issues. Foam board glued the wall and drywall glued over it, foam should covered with a firebreak material, no need for studs. Make sure you observe the HWT and furnace clearances.

My neighbor did not and when the reliance tech came to replace his HWT they redtagged his equipment due to insufficient clearances.
zzzz24 wrote: I am finishing my basement which was completely gutted, the exterior wall framing is done, and recently had it all spray foamed.
For the furnace/hot water tank area, I was advised they wouldn't do it in there because of a fire hazard.

My issue is, the area the hot water tank and furnace are in is quite limited for space, so the spray foam was really the only option to insulate the walls. It is a small house, and the furnace and hot water tank are located in one corner of the basement side by side. I could possibly cut and slide some rigid foam board insulation in there, but it would still be tight. There would not be enough room behind the water heater for example, to then install studs for drywall, etc. over top of the foam board.

It just seems weird to insulate and finish the majority of the basement, to then leave the furnace area exposed with concrete block walls.

Anyone have a small furnace room and what did you do to insulate it, if anything? Or if space is an issue is it normal to just leave this area exposed?
Deal Addict
Nov 2, 2011
3055 posts
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2000teamti wrote: Yeah you should insulate as you may have condensation issues. Foam board glued the wall and drywall glued over it, foam should covered with a firebreak material, no need for studs. Make sure you observe the HWT and furnace clearances.

My neighbor did not and when the reliance tech came to replace his HWT they redtagged his equipment due to insufficient clearances.
My hot water tank is probably too close to the wall as it is, Wouldn’t be enough room to do foam board and drywall on top of the wall behind it.
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Mar 13, 2004
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Many people do not finish the furnace room, its usually closed off anyways so you wont see it. If you want to put some sort of insulation on the wall (assuming its an exterior wall then you can do so. For interior walls & ceilings you could add some sound proof Roxul to help with the sound a bit but other then that I would not put drywall or anything as there is no much point.
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Feb 11, 2007
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Get Rockwool boards. Fireproof and could easily be removed.
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engineered wrote: Get Rockwool boards. Fireproof and could easily be removed.
Thanks I was not aware of this type of product and I also wanted info like Op asked. Just have to read and how easy is to install for me and other required procedures. I am using as storage but furnace and w/h have good space.
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Nov 2, 2011
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sickcars wrote: Many people do not finish the furnace room, its usually closed off anyways so you wont see it. If you want to put some sort of insulation on the wall (assuming its an exterior wall then you can do so. For interior walls & ceilings you could add some sound proof Roxul to help with the sound a bit but other then that I would not put drywall or anything as there is no much point.
Yeah I get that, it just seems odd that everyone finishes 90% of the basement putting all this effort in for insulation, but then leaving another area kind of exposed.
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Nov 2, 2011
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engineered wrote: Get Rockwool boards. Fireproof and could easily be removed.
Interesting, didn’t know they had fireproof stuff. This doesn’t look very rigid though like the xps boards, more like cutting bread in the reviews. How would I get it to stay on the walls without them sitting in the cavity of studs? It seems like it’s not rigid enough on its own?
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zzzz24 wrote: Interesting, didn’t know they had fireproof stuff. This doesn’t look very rigid though like the xps boards, more like cutting bread in the reviews. How would I get it to stay on the walls without them sitting in the cavity of studs? It seems like it’s not rigid enough on its own?
here is some info from the pdf guide I am reading now.

https://images.homedepot.ca/s7viewers/h ... 737930.pdf
https://www.homedepot.ca/product/rockwo ... 1000737930
"Laws for thee but not for me!" I will keep on jet-setting around the world. Spend as much as I can and enjoy vacations Free at Friends estate. Do as I do not as I say. I used to pay for my vacation until I met my hero.
Jr. Member
May 12, 2021
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Your HWT will eventually need to be replaced, when it does you can move it off the wall and complete it to your satisfaction.
zzzz24 wrote: My hot water tank is probably too close to the wall as it is, Wouldn’t be enough room to do foam board and drywall on top of the wall behind it.
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Feb 11, 2007
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zzzz24 wrote: Interesting, didn’t know they had fireproof stuff. This doesn’t look very rigid though like the xps boards, more like cutting bread in the reviews. How would I get it to stay on the walls without them sitting in the cavity of studs? It seems like it’s not rigid enough on its own?
You can go for the comfort board if you need something more rigid. Just glue or strap them to the wall.
https://www.homedepot.ca/product/rockwo ... 1000737930
If the women don't find you handsome, they should at least find you handy.

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