Twin wall flue through polystyrene ICF detail

[Kernow]

Does anyone have any details showing how they have taken a twin wall wood burner flue through a polystyrene ICF wall?

 

Originally the flue exited through the roof, but now we are thinking about exiting it through the wall and up externally. 
 

Would a simple 45degree sleeve cast into the wall work?

 

Thanks

[Joe]

Hi, I need to install a stove and flue in a new ICF build also but I have yet to find a stove company that has any experience of this, do you have a contact?

 

Many thanks,

[Temp]

Many years ago (13) I found this company very helpful when I needed special register plates for a woodburner. When I visited them there were signs up about Hetas training courses they were either running or organising. They seem to know their stuff. Perhaps give them a try..

 

https://www.specflue.com/

 

https://www.specflue.com/product-info

 

 

 

 

 

Edited May 6, 2021 by Temp

[Bitpipe]

Have you run the heat loss calcs on a ICF build to understand how useable your wood burner will be?

 

We rejected even a small ethanol burner as the 3kw output would have lead to gross overheating of our house - given our high levels of insulation & airtightness.

 

Also the govt direction of travel seems to be against wood burning due to the particulates  - I see wet wood and coal outlawed this week. Makes you wonder how long before any kind of domestic wood burning is restricted.

 

 

[FM2015]

On 02/05/2021 at 20:42, Kernow said:

Does anyone have any details showing how they have taken a twin wall wood burner flue through a polystyrene ICF wall?

 

Originally the flue exited through the roof, but now we are thinking about exiting it through the wall and up externally. 
 

Would a simple 45degree sleeve cast into the wall work?

 

Thanks

Currently got just this issue on one of our builds.  Are you planning on twin walling everything from "pot" to stove?

 

If yes, hetas are apparently happy with 50mm of clearance to anything combustible....this also include plasterboard....the paper is flammable.

 

Sleeve needs to be a maximum of 45 from vertical.  If you are pre pour, a sleeve with at least 50mm larger diameter than twinwall is ideal.

 

We have had differing views of what protection the EPS needs behind and around the actual stove.  Current job has a 4kw stove in a room with no fireplace, it's just in the corner.  If you have a fireplace, it's a bit easier to make tidy.  Ours is a nightmare.

 

Remember, no void space is of paramount importance.  So, either agree a build up directly onto EPS or take the EPS off back to the concrete.  Speak with hetas as they offer good advice and give you something to approach the installer with.

Dom

[Kernow]

On 06/05/2021 at 14:42, Bitpipe said:

Have you run the heat loss calcs on a ICF build to understand how useable your wood burner will be?

 

We rejected even a small ethanol burner as the 3kw output would have lead to gross overheating of our house - given our high levels of insulation & airtightness.

 

Also the govt direction of travel seems to be against wood burning due to the particulates  - I see wet wood and coal outlawed this week. Makes you wonder how long before any kind of domestic wood burning is restricted.

 

 

We have an unlimited supply of free wood, so it’s a logical solution for us. My understanding is that it is wet wood that has been banned, nothing wrong with properly seasoned wood. 
 

The heat issue was considered, but it is something that was always going to be included, even if it’s only used occasionally

[Kernow]

On 06/05/2021 at 14:56, FM2015 said:

Currently got just this issue on one of our builds.  Are you planning on twin walling everything from "pot" to stove?

 

If yes, hetas are apparently happy with 50mm of clearance to anything combustible....this also include plasterboard....the paper is flammable.

 

Sleeve needs to be a maximum of 45 from vertical.  If you are pre pour, a sleeve with at least 50mm larger diameter than twinwall is ideal.

 

We have had differing views of what protection the EPS needs behind and around the actual stove.  Current job has a 4kw stove in a room with no fireplace, it's just in the corner.  If you have a fireplace, it's a bit easier to make tidy.  Ours is a nightmare.

 

Remember, no void space is of paramount importance.  So, either agree a build up directly onto EPS or take the EPS off back to the concrete.  Speak with hetas as they offer good advice and give you something to approach the installer with.

Dom

 

Yes we were thinking twin wall straight up through. 
 

In the end we have ended up going out through the roof, due to a few factors. Mainly position of the flue on the exterior. 
 

One of the biggest challenges we considered was how to accurately position the sleeve pre pour having not chosen a specific stove yet. 

[Russell griffiths]

The easiest way to run it through the icf, is to not be over critical with location, if you think you need a 150mm hole running up at an angle then make a 450mm square void in the icf. 

 

I would cast in a 450mm square of eps into the core of the icf, then you can cut your hole wherever you want just by chewing out a bit more eps, no concrete bashing to do. 

 

So big hole, centre flue, repair around it. 

[FM2015]

4 hours ago, Russell griffiths said:

The easiest way to run it through the icf, is to not be over critical with location, if you think you need a 150mm hole running up at an angle then make a 450mm square void in the icf. 

 

I would cast in a 450mm square of eps into the core of the icf, then you can cut your hole wherever you want just by chewing out a bit more eps, no concrete bashing to do. 

 

So big hole, centre flue, repair around it. 

Good idea, a box would also work.  We had to be super specific to tie in to an isokern pumice DM system and followed the plans only to find that architect and hetas don't agree.  Our 4kw stove "needs" twin wall through the wall.  Installer not happy with a sleeve, of say, size above single wall flue. So our hole is closer to 600 high.  At what point does it become a window needing specific reinforcement?  

 

Personally, it's an area of regs that suffers from only affecting a very small number of builds.  Not enough examples to create a single accepted method.

 

Interestingly, a number of ICFs get their firerating when fixing plasterboard directly to EPS.  If you batten it off, you can't get the fire rating.  The void acts as a chimney.....then Grenfell happened.  So hidden voids should be designed out of internal surfaces.  Hetas recommend a board product for behind stoves that needs standing off the background.  Contradictory? Confused?  The manufacturers should be working harder in these areas.

[Kernow]

23 hours ago, Russell griffiths said:

The easiest way to run it through the icf, is to not be over critical with location, if you think you need a 150mm hole running up at an angle then make a 450mm square void in the icf. 

 

I would cast in a 450mm square of eps into the core of the icf, then you can cut your hole wherever you want just by chewing out a bit more eps, no concrete bashing to do. 

 

So big hole, centre flue, repair around it. 

This is a good idea, definitely would take the guess work out of it