Flexi flue liner - Yes or No?

Southern Comfort

I'm going to have a solid fuel stove installed in our holiday home.

The house was built in 1999. We bought it recently and it wasn't used much by the previous owner. The fire wasn't lit there much either. It has an 8 inch (200 mm) clay flue.

I'm putting in a Dimplex Westcott 8 kW stove. The flue pipe is 6 inch (150 mm).

Do I need to put a flexi flue in the chimney? Should I put one in? Some people tell me that there's no need because there's only a 2 inch difference between the flexi and existing one. Others say I should err no the side of caution and put one in.

I honestly don't know what to do so I would appreciate the opinions of those of you who know a bit about about chimneys and solid fuel stoves.

Thanks.

P. S.
Two storey townhouse over a separate ground floor apartment. Chimney shared with the ground floor apartment which has an open fire.

my3cents

Its nothing to do with the diameter of the flue (although that is a consideration), the problem is the amount of heat the flue can absorb.

Traditional open fires wasted 60% of the heat up the chimney that heat warmed up the chimney so that the exhaust gases stayed hot enough for them to exit the chimney. With a stove far less heat goes up the chimney so the chimney stays cold and the tar in the smoke cools and is deposited on the sides of the chimney.

There is an additional issue in that the tar often drops back down the chimney and collects around the adapter used to connect the stove to the chimney and/or at any joints at that back of the stove. This increases the chance of a chimney fire or a blocked chimney while the stove is running.

A liner has far less thermal mass so gets warm enough with the smaller amount sof waste heat to keep the exhaust gases from condensing.

I have a stove connected without a liner and in the winter to keep it safe to use the chimney needs sweeping once a month.

Edit> If you are actually sharing a single chimney all bets are off, you need someone to take a look and confirm exactly what can and can't be done, each stove/fire place has to have its own flue.

crock!

A liner is always a good idea and best practice..if you are thinking of using the 8inch flue then it would be a good idea to have someone sweep it and check the condition of it with a camera inspection before installing stove.

Southern Comfort

my3cents wrote: »

Its nothing to do with the diameter of the flue (although that is a consideration), the problem is the amount of heat the flue can absorb.

Traditional open fires wasted 60% of the heat up the chimney that heat warmed up the chimney so that the exhaust gases stayed hot enough for them to exit the chimney. With a stove far less heat goes up the chimney so the chimney stays cold and the tar in the smoke cools and is deposited on the sides of the chimney.

There is an additional issue in that the tar often drops back down the chimney and collects around the adapter used to connect the stove to the chimney and/or at any joints at that back of the stove. This increases the chance of a chimney fire or a blocked chimney while the stove is running.

A liner has far less thermal mass so gets warm enough with the smaller amount sof waste heat to keep the exhaust gases from condensing.

I have a stove connected without a liner and in the winter to keep it safe to use the chimney needs sweeping once a month.

Edit> If you are actually sharing a single chimney all bets are off, you need someone to take a look and confirm exactly what can and can't be done, each stove/fire place has to have its own flue.

Thanks, My3cents.

I'm sharing a chimney that has 2 separate clay flues and 2 chimney pots. Did you think we shared one clay flue? Is it safer than you thought?

my3cents

Southern Comfort wrote: »

Thanks, My3cents.

I'm sharing a chimney that has 2 separate clay flues and 2 chimney pots. Did you think we shared one clay flue?

Had to be said because I have come across chimneys that are shared where there is one flue shared between two fireplaces.

Southern Comfort

my3cents wrote: »

Its nothing to do with the diameter of the flue (although that is a consideration), the problem is the amount of heat the flue can absorb.

Traditional open fires wasted 60% of the heat up the chimney that heat warmed up the chimney so that the exhaust gases stayed hot enough for them to exit the chimney. With a stove far less heat goes up the chimney so the chimney stays cold and the tar in the smoke cools and is deposited on the sides of the chimney.

There is an additional issue in that the tar often drops back down the chimney and collects around the adapter used to connect the stove to the chimney and/or at any joints at that back of the stove. This increases the chance of a chimney fire or a blocked chimney while the stove is running.

A liner has far less thermal mass so gets warm enough with the smaller amount sof waste heat to keep the exhaust gases from condensing.

I have a stove connected without a liner and in the winter to keep it safe to use the chimney needs sweeping once a month.

Edit> If you are actually sharing a single chimney all bets are off, you need someone to take a look and confirm exactly what can and can't be done, each stove/fire place has to have its own flue.

my3cents wrote: »

Had to be said because I have come across chimneys that are shared where there is one flue shared between two fireplaces.

Thanks again. After reading what Crock and yourself posted, I think it makes sense to do it right and put in the flexi flue.
I presume it should be 6 inch like the stove flue. Does the vermiculite keep the flue warm to prevent the gases from condensing?

I'll need 6m of flue. What's the approximate cost of that? And would it be easy enough for the installer to put in given that the house is relatively new?

my3cents

Southern Comfort wrote: »

Thanks again. After reading what Crock and yourself posted, I think it makes sense to do it right and put in the flexi flue.
I presume it should be 6 inch like the stove flue. Does the vermiculite keep the flue warm to prevent the gases from condensing?

I'll need 6m of flue. What's the approximate cost of that? And would it be easy enough for the installer to put in given that the house is relatively new?

Just do a bit of research and check out the specifications of what you can get hold of. There are two grades of liner 316 and 904 with 904 being the better one but 316 is fine for most uses and if you can vermiculite around the liner that will help out. Everything is now 6 inch and there is hardly any difference in price with the older 5 inch. I think 6 inch is the norm now because you can get away without sweeping it for longer - very Irish.

6m is a fairly standard length so provided you don't need more than 6 m and use 316 grade you can get away with prices like this http://www.greenheat.ie/product/6m-6-inch-flexible-flue-liner-kit/ but 940 will start at around €300 just for the pipe and no other fittings.

The only thing I'd be keen to ensure is that whoever does the instillation does it in a way that leaves it easy to sweep the chimney.

A neighbor is a retired plumber who has installed a lot of stoves locally and the odd one he has done he's left it very difficult to sweep and even with a liner you need to sweep them at least once a year (but twice is better).

Southern Comfort

my3cents wrote: »

Just do a bit of research and check out the specifications of what you can get hold of. There are two grades of liner 316 and 904 with 904 being the better one but 316 is fine for most uses and if you can vermiculite around the liner that will help out. Everything is now 6 inch and there is hardly any difference in price with the older 5 inch. I think 6 inch is the norm now because you can get away without sweeping it for longer - very Irish.

6m is a fairly standard length so provided you don't need more than 6 m and use 316 grade you can get away with prices like this http://www.greenheat.ie/product/6m-6-inch-flexible-flue-liner-kit/ but 940 will start at around €300 just for the pipe and no other fittings.

The only thing I'd be keen to ensure is that whoever does the instillation does it in a way that leaves it easy to sweep the chimney.

A neighbor is a retired plumber who has installed a lot of stoves locally and the odd one he has done he's left it very difficult to sweep and even with a liner you need to sweep them at least once a year (but twice is better).

Thanks again for all that info and for taking time to post it.

Can I ask you a stupid question...... How does one sweep a chimney with a flexi liner in it?

crock!

With the liners.316 is good with sticks and turf and oil.904 is great for all above and plus coal.as for sweeping.if it's flued from the top then put in a cleaning eye.if flued from the back then it's more difficult to sweep with a brush.when you get a sweep then make sure it's someone that does power sweeping.there special rods and methods will do it no problem . Clean it twice a year.remember when fitting you need a vent and no wooden fire surround.you also need a carbon monoxide alarm.600mm of steel before attaching a liner.

Robbie.G

Southern Comfort wrote: »

Thanks again for all that info and for taking time to post it.

Can I ask you a stupid question...... How does one sweep a chimney with a flexi liner in it?

A flexi liner can be swept like any other flue but you must use special nylon brushes as they done scrape and damage flue.
If you fit a stove you must leave sweeping access

my3cents

Sweeping depends If you have a dead straight chimney and can look up it and see straight up to the sky then you can use ordinary drain rods with a suitable brush, but again that is dependent on having good straight line access to the liner from the bottom. If on the other hand you have bends in the stack then you should use much more flexible rods made for the job that won't damage the liner. The right brush is also essential as the over sized brush you use on an 8 inch brick flue can easily get stuck in a liner plus the cap can stop you pulling it back down.

For a liner the brush only just touches each side but its much deeper top to bottom than the traditional sweeps brush.