Woodburner - Flue Insulation

[Gabe]

Any views, I am installing a woodburner into our inglenook fireplace, plus one other into a smaller fireplace. I am planning to use double skin/twin walled flexible liners for both. I was also planning to insulate both with Rockwool wrap around insulation and this adds about another 600euros to the job. In other's experience is this a neccessity, only required for the larger inglenook/chimney, or over the top ?

All views welcome.

Gabe

[Llwyncelyn]

Hi Gabe now nothing about the technical side.  However currently in France if you buy a wood burner that meets the criteria of being 'green' and this is installed by an approved dealership then you get 40% allowance of the cost against ones tax.  Just had it and not only does the wood burner work well but the reduction in tax was also helpful

[Deimos]

I believe the tax credit has increased to 50% for installations in 2006. I was expecting 40% but they didn't install mine until first thing Jan this year and then the paperwork came through with 50% on (though obviously I don't get that until next year).

Ian

[Deimos]

I'm sure others have more experience (though I think most people get it done professionally due to the tax credit, 5.5% TVA, etc.).

However, when mine was done they installed small vents top and bottom to ventilate the chimney (i.e. the bits between the flue liner and the chimney walls) - presumably as you might get come condensation or just to stop mould, or whatever. The top vent is just a short bent tube (U facing down so rain does not get in) and the bottom just a grill. I don't know how filling the chimney with rock wool will affect the air movement (nor if the air movement is important).

Also, why are you thinking of adding all the extra rock wool ? To what ends/aims. It will keep the heat in the flue/chimney thus helping the fumes stay hot until they get outside. For me, I am not too concerned about what temperature the fumes are when they come out from the end of the chimney.

Ian

[Bob T]

If the fumes up the liner are allowed too cool before exitiing the chiminey, they will condense on the sides and line it with tar and soot. You would then need to sweep more often. I don't think that there is any need to add more insulation, as long as the liner is within a chiminey and the air up and down the sides of the liner is restricted so that it can heat up.

[Gabe]

As Bob T says, the idea of the insulation is to ensure that the flue stays hot and does not allow condensation and collection of deposits on the liner before it is vented to atmosphere. Often smaller chimneys are back filled with a small bead thing called leca or similar. This is impractical in a large sized inglenook, hence the use of lagging/insulation. Anybody else got any ideas ?

Gabe

[Iain]

From anecdotal evidence, the performance of flues seems to vary a lot between specific locations/installations; I would imagine though that the taller the chimney, the more the requirement for insulation, as the flue will cool more & more as it goes up. Personally I wouldn't use any insulation unless you find the flue starts getting clogged. Just capping the top of the chimney may stop enough heat escaping to prevent build up of soot in the flue.

This is just my personal opinion - I'm certainly no expert.

Iain