Fitting woodburner/multifuel in concrete chimney

Find a good chimney sweep and ask them. Ours proved to be a mine of information about what smoke would attack what kind of chimney.

Unfortunately the answer can often be 'yes, get a liner just in case' it seems.

Good idea! I didn't want to ask a fitter in case he tried to pull the wool over my eyes.

short answer yes for optimum performance the size of flue will be determined by the woodburner, if the chimney was designed for an open fire the chimney is likely to be larger than this. thats not to say it would not perform adequately. Ive not come across a solid concrete chimney before, has it not got clay liners in it? anyway play safe and install a flexible stainless steel liner (in a single length). If you have enough room get an insulated liner, otherwise insulate in situ

Do you mean aside from the legal requirements?

My view is that if you are burning wood and the stove is closed then yes you should have a liner. OTOH the risks of living dangerously may only be cosmetic. BTW I do not have a lot of faith in a chimney sweep being able to shift tarry deposits.

The reason is if the dew point of the flue gases from logs is higher than the chimney temperature then a tarry condensate can form in the chimney. With an open fire there is normally enough dilution air drawn from the room to keep the rh low and the gas velocity up. With a wood stove on low heat flue gas velocities will be low and the concrete mass takes a while to warm up.

The more efficient your stove is at extracting heat from the wood to the room the colder the flue gas will be. In order to vent the stove at the lowest temperature (say 160C for average logs) you need the chimney to be well insulated with low thermal mass and maintain gas velocity by not changing cross section.

With smokeless coal this is not an issue.

Manufacturers of wood burning devices go to some lengths to avoid a condensing mode so the requirement is quite different from a modern gas boiler.

AJH

Thanks, but why don't I just fit the wood burner and see if every thing works OK? I checked with a local chimney sweep, and he said there should not be any problems with it (providing it's swept and smoke tested).

Is there a legal requirement for woodburners to have a flue inside a chimney?

But if regular sweeping of an ordinary chimney prevents chimney fires, would not more regular sweeping of a stove chimney do the same?

Flue liners are absolutely required with any stove these days. IIRC.

Flexible is only permitted for chimneys pre 1969 vintage I think.

You may need a solid double insulated very expensive stainless steel one. I did :-(

Cost exceeded the stove...

Because its a breach of building control, and may make your house uninsurable if you tell the compoany, uninsured if you don't, and unsaleable.

If the BCO finds out, you can be fined and ordered to remove the stove.

Its not a question of whether it will work, its a question of whether it meets fire safety and building control regulations..and whether you are prepared to face the consequences of breaking them.

Unless the flue is specifically constructed for a wood burner.

AJH's rationale makes complete sense to me. I have set fire to wood burning chimneys (unlined) on 5 occasions. Condensation of tars is a huge issue.

Now a chumney fire is NOT the end of the world. But if it burns your house down and there is fine print in the insurance that says its not their problemn if you have breached rules and done a cowboy installation......

Its not that easy to sweep a stoved chimney - getting the brush up from the stove is a difficult thing.

They made me use a double skinned insulated heremetically sealed flue. Doesn't need sweeping, and,if it does catch fire, there won't be much of a problem :D

Cost about 700 quid IIRC.

Well our chimnay sweep had no issues with doing it, just part of a normal day's work.

I think they *do* need sweeping, maybe not as often as a brick chimney would but we've certainly been advised to have ours checked/swept annually.

Whoa! Liner or no liner, the right way to vary the output of a wood stove is by the amount of wood being burned, not by restricting it's supply of air. (When all the wood has burned to embers is the only time the supply of air may be restricted.)

Also adding the wood bit by bit and using well seasoned (ie fairly dry) wood is a great help.

Think of what is needed for a smoke free bonfire, after all a stove is a bit like a bonfire in a box.

The EPA stoves in the US use an 'afterburner' to burn flue gases completely:

cheers, Pete.

That may be the right way, but most wood burners work on air restriction.

If yuu have nothing better to do..

OTOH loading it all up and cooking it as in a charcoal burner on low heat, bolisd off te steam firts, then the lighter tarry fractions, then teh tars, l;evaing nicce charcoal later on :-)

I don';t think you can get away from te fact that most wood - even well seasoned wood - has a lot of tarry stuff in iyt as it burns..

...and that is how you do it in a commercial professional setup.

Sadly, its a buit pricey for domestic use.

^^^ _don't_

..and it stops you spending a few seconds now and then adding wood.

Any neighbours downwind will thank you, not! and you can look forward to a chimney fire more often.

Also heat is lost evaporating water and then tar from the wood, though a little is recovered when it condenses in the chimney...

..which will burn completely given heat and air to create flames, more heat and not smoke.

They are becoming the norm in the US.

Here, we make do with nannying legislation requiring expensive flues, so 'darwin at work' types can safely burn wood in the most inefficient polluting way.

cheers, Pete.