Existing chimney flue vesrus recommend flue liner

[wetdrip]

Existing chimney flue versus recommended flue liners
How do I know if the draw on my existing chimney flue is good enough for a multifuel woodburning stove, so that I do not need to install a flue liner.

Let's say the smoke test has been performed and no leakages have been detected.
Let's say my existing 1930's chimney flue is 11" across.
Most of the companies selling woodburners recommend you have them install their, or a flue liner; these being roughly 5" - 7" inches in diameter, opposed to the pre existing 11" chimney flue.

They state it's a lot do with the temperature of the flue the smoke's escaping up, and a cold chimney flue will slow or stop hot air (smoke) rising.I'm kind of doubting a lot of what's said, and see it as a means to extract cash from my wallet.
Any thoughts?

 

[Reg Man]

Stove manufacturers would not specify flue lining unless it was necessary.

 

[Kemble]

If it was in my house... I'd definitely fit a liner and backfill with vermiculite... it's a no-brainer !

 

[Mugwuffin]

Talk to some HETAS registered installers they can give you the correct advice, I may be wrong but think fitting a new log burner to an unlined chimney is now against building regs

 

[AWheating]

they can be fitted without but there can be problems.
one major problem that can come from not using a liner is alot of condensation. Ive seen black/sooted condensation leech through plasterwork. Its best to line and back fill as suggested above to avoid any such issues and get a good flue performance.

 

[johnnyplumb]

I don't deal with solid fuel only gas but I would imagine these multifuel stoves have increased in efficiency from the stoves of old.
increased efficiency is good, but it can cause other problems, ie it can effect the flues ability to clear poc, mainly due to density differences between hot gases and the colder surrounding areas.
this is probably why manufacturers recommend a liner.

 

[lame plumber]

massive soot build up and fire risk seems to be one reason use use a liner from seeing the result of not using one

 

[MarkOil]

I've heard before that you shouldn't use vermiculite as it can absorb moisture and then cause dampness in walls, or is that just for oil boilers? are wood burners different?

 

[Best]

I've heard before that you shouldn't use vermiculite as it can absorb moisture and then cause dampness in walls, or is that just for oil boilers? are wood burners different?

Vermiculite will absorb & retain massive amounts of water & I assume Perlite insulation less so.
All you can do is water proof chimneys outside as much as possible & probably use Perlite.
Oil or solid fuel into chimneys will make little difference if damp getting through, although solid fuel chimneys can be hotter & constantly hot while fire lit.
What concerns me is if a liner ever gets a hole eventually, then dry filled insulation will pour into liner/boiler like salt.

 

[Best]

Back to the original post,
An old chimney of, what you say is perhaps 11" across which is usually not round like a liner but square. Have you ever considered the hugh volume difference of a chimney of that construction compared to, say a 8"internal clay liner? And also then the volume difference between a standard 8" clay liner & a 6" or 5" stainless steel liner, whatever the MIs of the stove needs? Any boiler solid fuel or oil will condense a lot worse in a larger flue & soak into the fabric of the building. Everything will congeal inside also. A round liner will be much easier to clean by a chimney sweep & if it is a proper stainless steel liner it will be the minimum & therefore correct size for the stove & will heat up as much as possible, letting the flue draw well & removing water into atmosphere. Any water running down inside a metal liner will evaporate.

 

[Worcester]

Multifuel stoves have a very high flue temperature, and it is almost certain that your existing chimney will not be suitable without a flue liner.
It is also almost certain that there will be some porosity in the brickwork that wouldn't be detected by a smoke bomb test, and that would mean flue gases escaping into upper rooms. Also there is no way of knowing what the internal condition of the existing chimney is - loose bricks, voids, sharp bends / angles, rapid changes in size etc etc

I doubt any Hetas or Bpec (yes there are alternatives to Hetas ) engineer would allow you to install it without a liner - we certainly wouldn't it's too risky. As I doubt the current chimney would meet the current requirements:
Temperature Class : 400°C
Soot fire resistance tested to 1000°C
Moisture resistance
Internal surfaces to to smooth and gas tight
Thermal insulation to prevent flue gasses cooling.
etc, etc

To name just a few

So in simple answer, no it's not just a method of extracting extra dosh, it's to make sure you don't get poisoned with CO ....

NOTE More people are poisoned from incorrectly installed multi-fuel burners each year than from faulty gas appliances ....

Don't risk your or your family's lives for the sake of a couple of quid.

 

[wetdrip]

Many thanks to all.

 

[Worcester]

Don't forget you must also have the flue swept at least twice a year, usually once at the start and once at the end of the heating season (October and April), else your household insurance could be invalid....

Before you look to shortcut, just remember - in Autsria it's a requirement 6 x a year

 

[wetdrip]

Don't forget you must also have the flue swept at least twice a year, usually once at the start and once at the end of the heating season (October and April), else your household insurance could be invalid....

Before you look to shortcut, just remember - in Autsria it's a requirement 6 x a year

Do you mean the stainless steel flue liner would have to be swept?

 

[Worcester]

Do you mean the stainless steel flue liner would have to be swept?

Yep, the BPEC/HETAS guidelines I've got says they MUST be swept twice a year, hence you should allow access to the flue for inspection and maintenance. - Usually a removable panel/plate/hatch See Building Regs Approved Document J Pages 11 and 26