Rock Wool against a manufactured chimney

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Woooody

Guest
We just installed a manufactured s.s. insulated chimney in our house which has a cathedral roof. I didn't use the manufactured "box" to suspend the chimney from the rafters. It is supported in the basement below on a wall mounted base support inside the building.

My question is about insulating the hole where the chimney exits the cathedral roof\:.

There is the normal galvanized tin fire block and radiation shield installed where the chimney goes through floors and cathedral roof. Everything is fitted according to regulation clearances. Can I install (or is it advisable or legal to install) rock wool directly against the radiation shield and against the chimney itself where it exits the ceiling and roof?

The reason for this is that I want to do a good job of insulating the chimney at the exit hole. I am told unofficially that rock wool insulation will not burn so there is no problem with doing what I propose. I did not buy the factory produced item that is used with cathedral ceilings as the chimney is not suspended from the rafters, as explained above.
 

MEngineer24

Member
Dec 6, 2020
108
WV
What brand of chimney did you install? I know for the one I have the install manual specifically states not to stuff anything between the pipe and roofline. Typically, the roof flashing is ventilated in order to pass heat from the pipe. In my mind, insulating the hole at the roof would prevent that from occurring.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
90,609
South Puget Sound, WA
The brand of pipe is important. Some companies sell insulation for this purpose with their product. When in doubt, call or write to their tech support.
 

xman23

Minister of Fire
Oct 7, 2008
2,352
Lackawaxen PA
I agree with what was said. Of course check the pipe manufacture. The ceiling box creates the clearance from the ceiling and rafters. I guess you could use a pipe ring to cover up the gap. With my insulated double wall I believe it was 2" to anything.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,609
South Puget Sound, WA
This is a common question. Selkirk makes the Selkirk Universal Shielding Insulation (SUSI) for this purpose. Wish other manufacturers did too.
 

CanFireman

Member
Mar 23, 2018
20
Canada
In Canada, you do have options to address this providing you use a product that is designed accordingly.

DuraTech Premium, DuraTech Canada, Secure Temp S2100 and Secure Temp ASHT all feature factory-insulated parts or parts that can be installed with rock wool. These parts are also vapor-barrier friendly.

The “RCS” support can be used in cathedral or vaulted ceilings. Rock wool goes inside the box and is in direct contact with chimney. Box can be filled top to bottom. Need more height? An extension is offered. It can be filled too.

If looking for a shield you can run chimney up through and insulate, have that too. Look for the “pass-through” radiation shield.

ASHT is available in some regions of the US.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
90,609
South Puget Sound, WA
Could be. Not sure. It might be ceramic wool. Regardless of material it is what is tested for their system and approved.
 
W

Woooody

Guest
Forum:

I just learned of an insulation product called Rocksul which is made of Basalt and metal slag. It has many excellent properties, one of which is fire resistance. It will withstand fire and temperatures up to around 2,100 F. (watch their video for exact specs) For one thing, it has application as a fire barrier insulation. there are others too.

If you search Youtube there is a good video explaining it's characteristics and properties.
 

MEngineer24

Member
Dec 6, 2020
108
WV
Forum:

I just learned of an insulation product called Rocksul which is made of Basalt and metal slag. It has many excellent properties, one of which is fire resistance. It will withstand fire and temperatures up to around 2,100 F. (watch their video for exact specs) For one thing, it has application as a fire barrier insulation. there are others too.

If you search Youtube there is a good video explaining it's characteristics and properties.
You should still check with the chimney pipe manufacturer before using it in this application fire proof or not. These manufacturers design these systems to vent/move heat a certain way (sometimes ventilated flashing) and it is intended to operate that way. Stuffing that area may inhibit the design intent of the chimney thus creating problems.
 
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CanFireman

Member
Mar 23, 2018
20
Canada
“Roxul” is rock wool (aka Mineral wool). This product is used within many brands of today’s solid-fuel chimney; however… you cannot just go ahead and stuff this wherever you like.

Open air-space is a requirement for most all chimneys. If you apply insulation within an area that should be open, overheating can occur.

Follow instructions. Do NOT improvise.

While on this topic: Too often, I see spray-foam being used. DO NOT DO THIS! Spray-foam is flammable!!
 
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