thinking of fitting a multifuel stove

sm_jamieson · 2013-04-13T18:18:33+00:00

I am thinking of fitting a multi-fuel stove, probably around 8kW. At the moment a standard open fire place exists. It has an "ash box" beneat h the grate with vents in it that are supplied with air from the underfloor void by a tube under the hearth. The fireplace and flue depth is 9 inches and the back of the flue is only a half brick thick, but is made of blue en gineering bricks and does not seem damp at all. The flue is open - no liner of any sort. The rest of the wall is solid 9" brick. The fireplace is on an exterior wal l. Fire surround with be traditional wooden painted white. I will have a carbon monoxide detector for obvious reasons. I have some questions. Hopefully this does not seem too lazy - perhaps a se ction could be added to the wiki eventually ... 1. Assuming a non-balanced flue stove, where is the air drawn in ? Can the inlet be connected to a duct so that it takes air from below the floor (whi ch has air bricks !) thus avoiding need for an exterior vent in the actual room ? 2. Is a flue liner required ? Is so what type of liner (rigid / double wall / insulated etc) ? What size ? (for say, 8 kW stove) 3. The chimney breast is not very deep and build partly into the wall (rear of flue only half brick. Is it OK for the stove to stick out proud of the non-combustible fireplace opening (possibly further than the fire surround also) ? How high above the stop of the stove must a painted timber fire sur round and mantel be ? 4. Do you need to fill around the liner in the flue with insulating materia l (presumably held in with a register plate) ? 5. The half brick back to the recess will need to be insulated in some way. Is celotex covered with some type of cement fire board be OK for regs ? 6. I will have to widen the fireplace from the 16" fire box. How much wider than the stove does the opening need to be ? 7. Is it safe to operate the stove with the doors open for short periods of time ? Thanks, Simon.

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Tim Watts 13 years ago

On Sunday 14 April 2013 01:08 The Natural Philosopher wrote in uk.d-i-y:

Unless the old chimney is dripping with tar I fail to see why?

Sure, the liner radiates a lot of heat[1], but I would be very impressed if that managed to cause hot jets of gas to blast through gaps in the mortar and still be hot enough to cause combustion.

[1] Which I regard as a good thing - it puts heat into the core of a huge lump of masonry right in the centre of my house which gives some background heat to other parts and acts as a buffer.

Mine is a single skin SS liner installed in a brick flue by a HETAS installer, with no vermiculite. Obviously his judgement was based on seeing the chimney.

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David.WE.Roberts 13 years ago

As far as I know there isn't any requirement for open fires.

Sensible to get it swept.

If it hasn't been used for 40 years then also sensible to have a smoke test to confirm no leaks - at my MILs the smoke bomb showed smoke coming out in between the bricks of the chimney.

I hadn't considered fitting a liner for an open fire - not sure how you would terminate it above the fireplace.

My thought would be to have the chimney checked by a sweep. If it appears sound then you are good to go. If it appears unsound and needs a liner then I would fit some kind of stove; not much extra cost after the liner and a much more efficient source of heat.

Cheers

Dave R

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Tim Lamb 13 years ago

In message , Tim Watts writes

I don't think you are allowed to use single skin for an enclosed woodburner. The insulated twin wall is sectional and costs several arms and legs. SS twin wall is little thicker than single but the inner scroll is lapped so that condensate can't penetrate. There is a little arrow to show which way is *up*.

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Tim Watts 13 years ago

On Sunday 14 April 2013 19:39 Tim Lamb wrote in uk.d-i-y:

If it was double, it didn;t look like it. How thick is double skin? Less than a cm?

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The Natural Philosopher 13 years ago

more like 4-6cm

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polygonum 13 years ago

Someone I know had a stove installed and the idiots who did it managed to do so with the arrows the wrong way up! What realistic difference is it likely to make? (Only for interest - not currently in contact with the person.)

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Tim Watts 13 years ago

On Sunday 14 April 2013 22:05 The Natural Philosopher wrote in uk.d-i-y:

Mine is single skin which is what I thought.

Before anyone argues, I trust the installer.

- Tim Watts Personal Blog:

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Tim Lamb 13 years ago

In message , Tim Watts writes

Yes. 5mm at a guess.

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Tim Lamb 13 years ago

I have a *left-over* length if anyone wants to experiment:-)

I think the idea is than any liquid tars condensing in the flue will trickle back down to the fire rather than finding their way through the liner and into the flue proper.

I guess condensing tars will depend on fuel, combustion temp. length of flue etc.

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Dave Liquorice 13 years ago

The sectional, mineral wool insulated. liner has 4 to 6 cm wall thickness.

The flexable twin wall liner is less than a cm thick, maybe less than 5 mm.

The flexable twin wall stuff does look like single wall at a casual glance.

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Dave Liquorice 13 years ago

As above the over lap of the strip making up the liner is such that when fitted the right way up any condensate flows down the inside of the liner. Fit it the wrong way up any condesate may flow out of the liner:

| Top | | Top | | | | | \ / || || \ / V || || || || / \ || || / \ | | | | | | | |

The join between the strips is not that simple, they interlock, but there is still a risk that the condensate will seep out.

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Tim Watts 13 years ago

On Monday 15 April 2013 08:28 Tim Lamb wrote in uk.d-i-y:

That's plausible then. I didn;t ask...

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thinking of fitting a multifuel stove

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