# Insulating around fireplace flue



## Hixheat1

BlueBSH said:


> Well, I have a open hole around the flue where it goes from the 1st floor up to the roof and cold air is just rushing down into the living room and master bedroom on which share the wall that the flue pipe goes down into, the area the flue goes into is a hallow void that is about 1.5" deep, and 12 ft wide that runs up to the attic and unforinuatly isnt sealed up around it up there... how would you go about weatherizing this? Pics attached where you can see the empty space and the pipe going through it... dispide what looks like paper touching it, its about 9 inches from it, its just the angle the picture was taken at.


It needs to be fire stopped code requires a 1 inch clearance from combustibles so use sheet metal and high temp caulking around flue cap rest of area with insulation too prevent drafting


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## BlueBSH

Hixheat1 said:


> It needs to be fire stopped code requires a 1 inch clearance from combustibles so use sheet metal and high temp caulking around flue cap rest of area with insulation too prevent drafting


 
well I know if needs a firespot around it at the joist level, I assume sheet metal with the firestop caul around all the openings that are left, but what do you mean by cap the rest of the area with insulation? how would I prevent the insulation from touching the flue pipe? thanks


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## Hixheat1

BlueBSH said:


> well I know if needs a firespot around it at the joist level, I assume sheet metal with the firestop caul around all the openings that are left, but what do you mean by cap the rest of the area with insulation? how would I prevent the insulation from touching the flue pipe? thanks


I'm going by Picts once you fire stop with metal and caulk that should prevent drafting u need too keep a one inch clearance from flue.


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## Hixheat1

Hixheat1 said:


> I'm going by Picts once you fire stop with metal and caulk that should prevent drafting u need too keep a one inch clearance from flue.


On the vert walls u need to have a vapor barrier we use a foil type barrier or in our industry we sometimes use our r8 insulation or bubble wrap It works well. Along with the insulation that is there. Without the barrier there is no r value and that is why it is cold around the fire place


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## Hohn

Why not something like a Roxul stone wool? It won't burn and is pretty dense to help reduce draftiness..


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## BlueBSH

Hohn said:


> Why not something like a Roxul stone wool? It won't burn and is pretty dense to help reduce draftiness..


no one carries rock wool around here on the shelf, not sure if I can special order a small amount from anyone, will have to check into that...


I do have a roll of that refletex bubble wrap insulation, but is that really the best thing to put an inch form a flue? should I do a sheet metal cover over the joist first to put something to prevent stuff from moving into the flue somehow on accident?


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## Hixheat1

Hohn said:


> Why not something like a Roxul stone wool? It won't burn and is pretty dense to help reduce draftiness..


Once you fire stop the drafting will stop k wool will help insulate around the flue. The vert walls still need a vapor barrier.


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## Termite

You CANNOT insulate up against that flue. No matter what type of insulation. All chimneys require at least 1" clearance, some require 2" or more. A sheet metal pan/collar around the pipe will seal up the draft when properly sealed with the aforementioned caulking. A sheet metal insulation shield....A cylinder of metal around the pipe sitting on top of the metal pan you need....Will keep any added insulation from contacting the flue and will maintain the necessary air space.


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## SteelToes

thekctermite said:


> You CANNOT insulate up against that flue. No matter what type of insulation. All chimneys require at least 1" clearance, some require 2" or more. A sheet metal pan/collar around the pipe will seal up the draft when properly sealed with the aforementioned caulking. A sheet metal insulation shield....A cylinder of metal around the pipe sitting on top of the metal pan you need....Will keep any added insulation from contacting the flue and will maintain the necessary air space.


Correct. Here in Chicago you need to have 1"-2" "cold air clearance" (depends on location); also looking at the picture it is hard to tell if this is a single or b-vent but in any case just like thekctermite said no insulation around the flue pipe only fire stop thimble at the floor perimeter.


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## BlueBSH

SteelToes said:


> Correct. Here in Chicago you need to have 1"-2" "cold air clearance" (depends on location); also looking at the picture it is hard to tell if this is a single or b-vent but in any case just like thekctermite said no insulation around the flue pipe only fire stop thimble at the floor perimeter.


how can you tell if its a B or L vent? I know one here requires 1 inch and the other about 3 inch clearance, not sure how you tell the difference.. Does the fireplace or manual specify what it should be or someway to tell from the cap on the flue or anything?

The fireplace is a Heatilator NA32

Edit: just saw on the tag on the fireplace 2 in min clearance chimney 1/2" firebox... guess that answeres my question, I guess its an L vent?


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## BlueBSH

or is it an L vent? 


> _Framing dimensions of enclosures and at joist or rafter levels shall be a minimum of 6" larger than the outside of the vent for L-Vent and 2” larger for B-Vent._


because the framing around it is not 6" on all sides, its more like 3" inches on 2 of the sides


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## operagost

I'm interested in this topic because I have a similar situation in my attic. My flue appears to be double-walled, as I have a mid-efficiency boiler yet the outside of the pipe is just warm to the touch when the boiler is running. I don't know whether this means I also need to add a collar or if I can just box it in with foam board while keeping a few inches of clearance. It's already boxed in where it passes through the second floor bathroom below, but I wouldn't want to add to a possible existing mistake.


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## SteelToes

BlueBSH said:


> or is it an L vent?
> 
> 
> because the framing around it is not 6" on all sides, its more like 3" inches on 2 of the sides


Type A b vent is intended for a low-heat applications
B vents are not for use with fireplaces and oil-fired equipment
_Type L-Vent is designed for venting approved oil or gas appliances producing draft hood flue gases not exceeding a temperature of 570ºF (299ºC)._
_Type B Gas vent is designed for venting approved gas appliances equipped with draft hoods and other Listed gas appliances specified for use with Type B Gas vent which produce flue gases not exceeding 480°F (249°C). _
_Minimum clearance between the vent and combustible materials is 3 inches for L-Vent and 1 inch for Type B gas vent. L-Vent or B-Vent that extends through any story above that on which the connected appliance is located is to be provided with enclosures having a fire resistance rating equal to or greater than that of the floor or roof assemblies through which they pass._
_Framing dimensions of enclosures and at joist or rafter levels shall be a minimum of 6" larger than the outside of the vent for L-Vent and 2” larger for B-Vent._
_Near the vent base, post a notice of the type of appliance for which the DFS installation to combustibles is installed. If installed at 1” airspace, it is limited to B-Vent (gas) only. If it is installed at 3” airspace, it it may be used with oil (as an LVent) or gas (as a B-Vent)._

for more info refer to this website :

http://www.inspectapedia.com/chimneys/L-Vent_Chimneys.htm​


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## kwerk

There should be a sheild that goes there and keeps the insulation away from the chimney. I would call the manufacturer and ask them about it, they may be able to send you the piece. There should also be a fireblock at each ceiling.

Scroll down to page 11 on here for an example:

http://www.heatilator.com/downloads/installManuals/480-1091.pdf


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## Michael Thomas

What is it venting? If it's a listed vent system, you would use the manufacturer's approved firestop and insulation shield, a typical example:


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## Termite

There's no need to fuss too much about getting an insulation shield from the manufacturer....One can be easily made with a piece of duct metal and a few sheet metal screws or rivets. Wrap the metal LOOSELY around the vent and fasten the ends together to create a circle. Just don't attach to the vent.

If the fireplace is a woodburner I'd say minimum 2" of clearance is a good average. If it is a gas logs unit it'll usually require minimum 1" clearance. When in doubt be safe and get a couple inches of clearance.


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## Michael Thomas

Around hare, if it's listed system, and the manufacturer makes a listed firestop and/or insulation shield, most AHJs want to see the listed components, especially at manufactured fireplaces. 

YMMV.


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## BlueBSH

well after not getting to this project I finally got around to it...

cut out the drywall in the inside the house chase to get full access, which really showed me how tight they built this to the flue..

I could now see the codes on the flue pipe, it is heatalator SL flue pipe (double walled) 8" Inner diamater, and 10" Outter

I ran the fireplace at full heat for a while to see how much the pipe heated up, used an IR camera and it only got to about 80 degrees out the outside, which isn't bad considering the ambient temp was in the mid 70's.

I made a firestop coller out of sheet metal in two pieces and allowed them to overlap by a few inches, sealed it all up with red high tempature caulk (the fireproof kind)

I still have to make an insulation dam, but not sure if I have room or not considering they took the bare minimum clearances and there is no more room to cut or move


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## akm

Similar situation, except will be trying to use oval (4" round equivalent) type-b flue pipe (for gas waterheater) up thru a 1-story (to get from basement to attic) exterior wall (gable-end, between 2x6 studs and insulation).
Should we provide a sheet metal 'chase' at min 1" clear of the flue pipe, in the wall framing, all the way (except at firestops) from basement to attic ?
Keeping it 1" clear (per local code) all the way up seems like a challenge, but I suppose with straps etc it could be done.
Or, is there another 'chase' material that could be used ?
Is there a good source (manual etc) for this type of installation ?
Thanks much for your help.


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## Windows on Wash

Best bet is to use sheetmetal and fireproof sealant to air seal the flue to the attic floor and build up a tall enough wall around it so that it does not get insulation piled up against it.


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