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Old 11-25-2008, 11:03 AM   #1
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expanding foam flamability


I have a house with an addition where the contractor went through the existing foundation to run a heat duct from the furnace. There is additional space surrounding the duct allowing hot and cold air to transfer from the basement to the crawl space. I was thinking about sealing it using an expanding foam but am not sure if there is fire safety issues putting the foam against a heat duct?

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Old 11-25-2008, 11:49 AM   #2
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expanding foam flamability


the ducts heat is not hot enough to ignite the foam, I would not worry about it. BOB.

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Old 11-25-2008, 11:50 AM   #3
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Most expanding foams are not rated to be exposed. The heat generated by the duct will never be enough to cause a fire problem, but the material itself can be very combustible. Look for a low expansion foam with a UL class A rating. Do NOT use a high expansion foam like Great Stuff. First, it won't have the class "A" rasting and second it will develop enough pressure to crush the duct. There are some companies like DAP that make a low ex fire proofing foam that may work, but be prepared to pay. Some fiberglass insulation tucked in the opening may do just as well.
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Old 11-25-2008, 10:31 PM   #4
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expanding foam flamability


You can find this at Home Creepo. http://greatstuff.dow.com/greatstuff.../fireblock.htm
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Old 11-26-2008, 11:53 AM   #5
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expanding foam flamability


Thanks James Con, I guess I'll have to modify my stements above. I was not aware that Great Stuff made a fire proofing foam. They also claim that their Great Stuff Crack and Crevice filler has a UL classification, but do not say what that is. If it is not class "A" rated for exposure, then stay away from it or cover it. There are a ton of UL ratings meaning a lot of different things.
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Old 12-01-2008, 11:20 PM   #6
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expanding foam flamability


Can the 'Great Stuff Fireblock' be used to cover a hot pipe going up through an uninsulated wall so that insulation can be blown in to fill the rest of the space? It's an exaust pipe for a hot water heater. It's hot to the touch before it goes up through the basement ceiling, it continues up through a wall cavity and goes through the attic and out through the roof. I don't know if the pipe is hot to the touch inside the wall cavity. In the attic, the pipe is just barely warm. The problem is that the wall cavity it goes through is uninsulated and very warm (probably over 80 F) because I think it is heated from the exaust pipe. The other problem is: as I'm standing in the attic, I can see down into the entire wall (10' long x 9" wide) because there is no drywall creating a 'ceiling' over that space. The heated air in that space is pouring up into and heating the attic. I covered the opening with OSB (for now) and the R-19 insulation that was already covering it. When I checked it yesterday, the OSB and R-19 are still letting a lot of the warm air flow up. I'm having cellulose blown-in within the next month and the guy who will possibly be doing the work said he can fill that wall with the the cellulose. I'm not sure he is taking the temperature of the pipe into consideration. Or, I can remove the OSB, so is there some kind of an insulation wrap or sleeve I could put around the pipe and slide it down the pipe into the wall cavity so I can have the insulation blown down around it into the wall cavity? I'm sorry if this isn't making much sense, but I would be thankful for any advice.
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Old 12-02-2008, 05:50 AM   #7
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expanding foam flamability


I would definitely advise against putting the insulation in the hot water exhaust pipe chase. being its a single wall pipe. if it was a triple wall than that's different. I would get a piece of wonder board and cut the dia. of the pipe in that then rip it in half then install it to cover the hole. where it comes up from the ceiling. Bob
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Old 12-02-2008, 08:22 AM   #8
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expanding foam flamability


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Originally Posted by gma2rjc View Post
Can the 'Great Stuff Fireblock' be used to cover a hot pipe going up through an uninsulated wall so that insulation can be blown in to fill the rest of the space? It's an exaust pipe for a hot water heater.
Heck no! Type B gas appliance vents require a minimum 1" clear space all the way around them to prevent combustible materials (like foam) from igniting. Having a flue like that in a wall is inherently dangerous. Code requires a metal insulation shield to surround the flue and prevent insulation from getting within 1" of the vent pipe.
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Old 12-02-2008, 08:28 AM   #9
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expanding foam flamability


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Originally Posted by buletbob View Post
I would definitely advise against putting the insulation in the hot water exhaust pipe chase. being its a single wall pipe. if it was a triple wall than that's different. I would get a piece of wonder board and cut the dia. of the pipe in that then rip it in half then install it to cover the hole. where it comes up from the ceiling. Bob
Hopefully it isn't a single wall pipe where it penetrates the wall or the ceiling. That would be illegal and HIGHLY UNSAFE. It has to transition to double wall before penetrating anything, and the clearance still must be maintained.
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Old 12-02-2008, 08:55 AM   #10
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expanding foam flamability


Thanks for letting me know that. It's easy to see why housefires start. If the insulation guy had filled that wall with insulation, there probably would have been a problem.

Where the pipe leaves the top of the water heater, it is (I'm guessing) 4" wide and just before it goes through the ceiling, it gets wider. Where it widens, I can put my hand on it, but for no longer than a couple seconds.

Again guys, thank you so much for your advice. Have a wonderful day.

Barb
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Old 12-02-2008, 07:19 PM   #11
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expanding foam flamability


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Hopefully it isn't a single wall pipe where it penetrates the wall or the ceiling. That would be illegal and HIGHLY UNSAFE. It has to transition to double wall before penetrating anything, and the clearance still must be maintained.
Yes that's what I was envisioning, A Single wall pipe! But then the poster said the pipe got larger as it went up the through the floor. So now 'm thinking double wall.
you want to keep the heat from escaping form the chase into the Attic , you could cover the top of the case hole with some sheet metal. nailed to the top of the ceiling beams with the pipe centered in the sheet.
What I would do, if the chase uses the backside of a room wall, they I would cut an AC grill in the wall just above the baseboard so to make use, of some of that heat that's coming off that pipe.
And install a carbon monoxide detector in the are of that room to make sure that pipe is correctly installed. and no gas is being expelled into the room.

Last edited by buletbob; 12-02-2008 at 07:27 PM.
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Old 12-03-2008, 10:48 AM   #12
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expanding foam flamability


Quote:
What I would do, if the chase uses the backside of a room wall, they I would cut an AC grill in the wall just above the baseboard so to make use, of some of that heat that's coming off that pipe.
And install a carbon monoxide detector in the are of that room to make sure that pipe is correctly installed. and no gas is being expelled into the room.
Thanks for the idea. I could put that grill in a hallway (near an existing CO2 monitor) or in a bathroom. Since hot air rises, would I put that high or low on the wall?

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