Wood stove liner and cowl

[JohnBishop]

Hi All,

   I want to re-commission my chimney for the wood stove and I also plan some roof repairs so I wanted to do this all at once.

I don't have the wood stove yet but the roofer told me I need to know the specification up front so they can install the correct liner for the wood stove.

This is going to be an average size wood stove outside the chimney, not a built-in one.

 

I reckon a flexible liner is enough but I have seen they install like ceramic or some other liners.

What would you suggest in this matter?

[Gus Potter]

Generally a single skin liner will be ok in an old brick flue that is not totally wrecked. Go for a good quality one.

 

Make sure you install the liner the right way up, see manufacturer's instructions at all times.

 

Have a look at the flue exit height. If you live in a town then other things may have been built round about later (taller buildings within say 200m distance, if near the Shard say in London then the vortices will extend much further) that will cause down drafts, if in the country you may have large trees that were not there when the house was built.

 

For the cowl have a look at an "OH" cowl.. more expensive but they do work and are great for counteracting down drafts and promoting a more stable draw in the flue.

 

If the flue is going to be long then to keep a good draw at low burn rates you can often put a single skin liner in an old brick chimney and pour in vermiculite. It keeps the flue warm so you don't cool the gases on their way up the flue. Important when you are just letting the thing tick over. Just make sure you have another baffle or rockwool above the register plate so when you service the stove the vermiculite does not all fall out. Again, ask your stove installer and find out what you think you will mostly burn in the stove and how you will be using it.. full blast occasionally or for mostly regular background heat.. big difference so choice range of stove performance is important.

 

Best thing to do is to take advice from a registered stove installer then feed back the info to the roofer.

 

 

Edited July 23, 2022 by Gus Potter

[Temp]

If the stove is going outside the chimney then some planning needed for the bottom end.

 

Typically would be a register/adaptor plate then cast iron pipe to the stove. The register plate may need a door in it for sweeping if not one in the cast iron pipe or it can't be swept through the stove.

 

Bends would normally be 45 degree max.

 

Should really be installed by a Hetas registered installer unless Building Control already involved.

 

Builder shouldn't really have to ask you for the spec as he should know.

 

[saveasteading]

Other than the smallest ones, new stoves in Scotland now must have a fresh air feed. At first I resisted but can now see the reasons.

ie I was going to put a closable grille nearby, for use only when needed. But of course this is subject to user knowledge, and ability.

A few stoves now have a dedicated air inlet at the back, but they are much more expensive. This is what we have shown on our Building Warrant application, so must shop around or hope that prices drop as it becomes standard.

 

 

11 hours ago, Temp said:

Builder shouldn't really have to ask you for the spec as he should know.

I didn't know until recently, and don't expect most builders to know either.

[Temp]

Deleted as posted to wrong thread.

Edited July 23, 2022 by Temp

[JohnBishop]

Thank you gents. That was very informative.

[JohnBishop]

On 23/07/2022 at 01:50, Gus Potter said:

Generally a single skin liner will be ok in an old brick flue that is not totally wrecked. Go for a good quality one.

 

Make sure you install the liner the right way up, see manufacturer's instructions at all times.

 

Have a look at the flue exit height. If you live in a town then other things may have been built round about later (taller buildings within say 200m distance, if near the Shard say in London then the vortices will extend much further) that will cause down drafts, if in the country you may have large trees that were not there when the house was built.

 

For the cowl have a look at an "OH" cowl.. more expensive but they do work and are great for counteracting down drafts and promoting a more stable draw in the flue.

 

If the flue is going to be long then to keep a good draw at low burn rates you can often put a single skin liner in an old brick chimney and pour in vermiculite. It keeps the flue warm so you don't cool the gases on their way up the flue. Important when you are just letting the thing tick over. Just make sure you have another baffle or rockwool above the register plate so when you service the stove the vermiculite does not all fall out. Again, ask your stove installer and find out what you think you will mostly burn in the stove and how you will be using it.. full blast occasionally or for mostly regular background heat.. big difference so choice range of stove performance is important.

 

Best thing to do is to take advice from a registered stove installer then feed back the info to the roofer.

 

 

I live in the countryside but you are right after all those years since the building was erected the trees are taller. The closest tree is about 2-3m higher than the nearby buildings. The closest tree is about ~16m away from the chimney.

This OH cowl is very clever. I have not seen these in the area.
I found one in here https://www.chimneycowlproducts.co.uk/acatalog/Stainless-Steel-Traditional-OH-Cowl-221.html

The also sell as a flexible flue fixing kit for extra £40.

I reckon the liner is going to be about 8m long.

In terms of the use the plan is to use it occasionally not as a regular background heat. For the fuel I only considered wood.
Yes I reach out to Hetas registered installers.

Edited July 24, 2022 by JohnBishop

[JohnBishop]

On 23/07/2022 at 14:59, saveasteading said:

Other than the smallest ones, new stoves in Scotland now must have a fresh air feed. At first I resisted but can now see the reasons.

ie I was going to put a closable grille nearby, for use only when needed. But of course this is subject to user knowledge, and ability.

A few stoves now have a dedicated air inlet at the back, but they are much more expensive. This is what we have shown on our Building Warrant application, so must shop around or hope that prices drop as it becomes standard.

 

 

I didn't know until recently, and don't expect most builders to know either.

Do you mean the DEFRA approved stoves that have this secondary combustion so there is less residue in the flue liner and it basically burns more efficiently?

[JohnBishop]

On 23/07/2022 at 01:50, Gus Potter said:

Generally a single skin liner will be ok in an old brick flue that is not totally wrecked. Go for a good quality one.

 

Make sure you install the liner the right way up, see manufacturer's instructions at all times.

 

Have a look at the flue exit height. If you live in a town then other things may have been built round about later (taller buildings within say 200m distance, if near the Shard say in London then the vortices will extend much further) that will cause down drafts, if in the country you may have large trees that were not there when the house was built.

 

For the cowl have a look at an "OH" cowl.. more expensive but they do work and are great for counteracting down drafts and promoting a more stable draw in the flue.

 

If the flue is going to be long then to keep a good draw at low burn rates you can often put a single skin liner in an old brick chimney and pour in vermiculite. It keeps the flue warm so you don't cool the gases on their way up the flue. Important when you are just letting the thing tick over. Just make sure you have another baffle or rockwool above the register plate so when you service the stove the vermiculite does not all fall out. Again, ask your stove installer and find out what you think you will mostly burn in the stove and how you will be using it.. full blast occasionally or for mostly regular background heat.. big difference so choice range of stove performance is important.

 

Best thing to do is to take advice from a registered stove installer then feed back the info to the roofer.

 

 

This vermiculite is a really good idea. I can see on the Internet they talk about insulation of the chimney so there is no/less condensation. Thanks.
Will contact local Hepas installers.

[saveasteading]

6 hours ago, JohnBishop said:

Do you mean the DEFRA approved stoves that have this secondary combustion

No. That is a very good thing and gets you a lot more heat as well as reducing ash.

 

I meant a specific air feed from outside to the back of, or even connected to, the stove. Search for 'wood burner external air feed'

 

[JohnBishop]

55 minutes ago, saveasteading said:

No. That is a very good thing and gets you a lot more heat as well as reducing ash.

 

I meant a specific air feed from outside to the back of, or even connected to, the stove. Search for 'wood burner external air feed'

 

Right, so in my case the chimney is in central location of the semi-detached house. It use to be another chimney on the other side but it was taken down.

I have seen someone talking about taking air from an air duct that runs in the floor but this would require me to demolish some of the concrete floor.

The neighbour has a hole in the wall for the fresh air for his gas heater so I reckon no other option was available for him.

 

This fresh air duct is an awesome idea and prevents the warm air in the room from being sucked into the chimney. I definitely ask the installers if this option is possible in my setting.

[saveasteading]

Is it a groundbearing floor or suspended? Pipe along the skirting? Doesn't have to be round.

60mm dia for a 5kW burner if I recall  and prorata mm2 for smaller or bigger.

[Roundtuit]

There are flue systems that can also supply an external air feed, but I expect they're expensive.   Anyone heard of running two flue pipes up the chimney to use one for an air feed?  You'd have to get some separation at the top end obviously.

 

[JohnBishop]

On 23/07/2022 at 01:50, Gus Potter said:

Generally a single skin liner will be ok in an old brick flue that is not totally wrecked. Go for a good quality one.

 

Make sure you install the liner the right way up, see manufacturer's instructions at all times.

 

Have a look at the flue exit height. If you live in a town then other things may have been built round about later (taller buildings within say 200m distance, if near the Shard say in London then the vortices will extend much further) that will cause down drafts, if in the country you may have large trees that were not there when the house was built.

 

For the cowl have a look at an "OH" cowl.. more expensive but they do work and are great for counteracting down drafts and promoting a more stable draw in the flue.

 

If the flue is going to be long then to keep a good draw at low burn rates you can often put a single skin liner in an old brick chimney and pour in vermiculite. It keeps the flue warm so you don't cool the gases on their way up the flue. Important when you are just letting the thing tick over. Just make sure you have another baffle or rockwool above the register plate so when you service the stove the vermiculite does not all fall out. Again, ask your stove installer and find out what you think you will mostly burn in the stove and how you will be using it.. full blast occasionally or for mostly regular background heat.. big difference so choice range of stove performance is important.

 

Best thing to do is to take advice from a registered stove installer then feed back the info to the roofer.

 

 

Speaking about vermiculite. One of many HETAS installers I have contacted has come back to me and said that they don't pour vermiculite because it's not recommended and leads flue to rot. 😀

[Gus Potter]

47 minutes ago, JohnBishop said:

Speaking about vermiculite. One of many HETAS installers I have contacted has come back to me and said that they don't pour vermiculite because it's not recommended and leads flue to rot. 😀

That's interesting. Did they explain why it leads "flue rot" and who does not recommend it?

 

Is it because often the flues are in bad condition and they end up getting the blame or is there a fundamental reason not to insulate using vermiculite? After all it is common to line a flue if it is a bit "leaky".. in less than perfect condition.

 

If you can find out as would like to know, Ta.

 

 

 

 

 

[JohnBishop]

Apparently vermiculate holds water. That was their explanation I have not fact checked it.

[Gus Potter]

Like your train of thought @JohnBishop

 

On the face of it you can use vermiculite for plant pots, good for retaining water apparently. I'll defer to others on BH but I don't think it is hydroscopic.. has been use a lot in the past for house insulation.

 

So yes it will hold water if it gets in. I suppose you need to make sure your chimney is in good order, capping, flashings, pointing render and so on. In some ways it may be good that it can hold the water, if not.. it's going to run out the bottom and onto the top of your stove or appear somewhere in the chimney breast above the stove as a big damp patch.

 

If you have your stove on regularly it should drive off any moisture, even if just on a slow burn.

 

The question is what else can you use to insulate a single skin liner that will get round all the contortions in a flue also given that a single skin liner when installed does not centre it's self in the flue.

 

Folk these days want to have a stove that will just tick over but still draw.. thus you need to keep the flue pipe warm.

 

 

 

 

 

 

 

 

 

 

 

 

[Simplysimon]

1 hour ago, Gus Potter said:

If you have your stove on regularly it should drive off any moisture, even if just on a slow burn.

aye, fine if he lives in se england, however, if he lives up here it rains in the 'summer' and may not dry out. just read, i think @Radianpost about his grass, we don't have that issue here, a dry day is still almost a novelty 😂

[Gus Potter]

3 minutes ago, Simplysimon said:

a dry day is still almost a novelty

Simon.. yes that is the joy of Scotland.. you get four seasons in one day.. the sheep are white.. lovely to look at as they get washed nearly every day.. our central heating kicked in this morning in part of the house.. summer in East Kilbride.

[Simplysimon]

7 minutes ago, Gus Potter said:

our central heating kicked in this morning in part of the house.. summer in East Kilbride.

yup, ours has been doing the same. EK is frightening as to how big it's got

[Gus Potter]

6 minutes ago, Simplysimon said:

yup, ours has been doing the same. EK is frightening as to how big it's got

Moved to EK about ten years ago as wife's family live here. One day I left the house I had bought and got lost in EK (called the roundabout city..) and it took me about two hours to find my way back.

 

 

[Simplysimon]

18 minutes ago, Gus Potter said:

Moved to EK about ten years ago as wife's family live here. One day I left the house I had bought and got lost in EK (called the roundabout city..) and it took me about two hours to find my way back.

 

 

ek not as bad as mk for roundabouts. was down there for a couple of courses, wow, and not in a good way

[Gus Potter]

For all.

 

We have a new bit of dual carriageway nearing completion in EK. One of the roundabouts has astro turf in the middle and nearby a big SUDS pond, probably designed by some that have not thought it through. What message does that send to the kids who go by it every day on their way to school? I wonder if when they designed the SUDS pond and the organisms you need to promote for them to work properly they thought about the micro plastics and initial filtration / first steps in the treatment train?

 

Although of SE bent the number of sites I visit where folk are astro turfing thier gardens is noticable. 

 

That said some boy racer has already churned a bit of it up. Well done son!

 

Will take photo and post next time I pass.

 

 

 

Edited August 7, 2022 by Gus Potter

[JohnBishop]

I got an after market 5kW stove Cast Tec Juno 5. I think it's a good choice.

The spec says that "The diameter of the flue should not be less than 150mm and not more than 200mm."

So the 5" liner is going to be used. How can I tell that the liner is of good quality?

 

I am replacing the glass on the stove and there is this thin foam around the glass? It disintegrated. What is it called?

Edited August 8, 2022 by JohnBishop

[markc]

No way to tell if a liner is good quality or not, just buy from a reputable source. It is not in a suppliers best interest to supply crappy materials or items but seconds do get sold on eBay etc.

last time I needed some sealer strip I googled stove door seal and found the stuff I needed