Chimney Advice for open fire

[Loki7430]

Good afternoon all;

New to the forum following a recent house move so sorry if this post has been answered elsewhere but I've done a search and found similar answers but not quite what I'm after....

We have a thatched house built in circa 1650, that currently has a disconnected multi fuel stove (so a small liner in the Chimney but not much else now). We want to get it removed and make it suitable for an open fire but have had three different sets of advice (apart from a taller pot that they all agree on to increase the height above the thatch to a min of 1m).

1st (insurance inspector). The existing liner is fine to use as, just need a hood.
2nd. The liner needs to be removed and insulated, and a hood installed before re-installing
3rd. They are both wrong, the liner is too small and needs to be removed completely, an open fire is fine to use without a liner.

So in short - subject to the condition of the chimney being okay once it is inspected following liner removal, is it okay to operate an open fire without a liner? What do I need to do/look at to ensure it is okay. Does anyone know of a reliable source I can look at?

Thanks

Ian

 

[mims&pip]

Bumping this back to the top as it was in danger of vanishing from the first page :wink:

 

[paulc]

You can run an open fire with a chimney liner or without one if you prefer. There are several online resources that will tell you what size the fireplace opening should be in relation to the area of the flue and also the optimum height.

Without a liner, the opening should be no more that eight times the cross sectional area of the flue.

With a liner, it is ten times the CSA - The reason being, a liner offers less resistance to the air flow, so you can get away with a larger fireplace.

If the original chimney is in poor condition, then a liner is worth having - But ideally, you won't want to burn regular house coal as the fumes tend to shorten the lifespan of the liner.

Having recently ripped out an open fire and replaced it with a cassette multifuel stove, I have found it much warmer in that room. Also, flying embers from a spitting fire is no longer a problem, so there is the safety aspect to consider.

Should a liner be insulated - That is open to debate. If the chimney stack is on an external wall, probably. If it is in the middle of the property or runs up a party wall, it doesn't need to be insulated. In the latter case, an uninsulated liner will help to heat the rooms above (if there are any). On the subject of insulating a liner, loose fill insulation such as vermiculite or foamed glass can be problematic if/when the liner needs replacing. It makes a lot of mess when the liner is removed, and if it had been mixed with cement, makes life difficult in removing the liner.

I opted to use a vermiculite/cement mix for insulation around the stove and loose fill part way up the gather. The remainder of the liner is uninsulated the rest of the way. But I have habital rooms upstairs and the chimney stack forms part of the party wall.

 

[MikeG]

I'm not sure that 1m above the ridge line is tall enough for the chimney. Let me put that another way. I am sure that 1m isn't tall enough. It should be 6 feet (1.8m). There is some good advice here:

http://www.chimney-problems.co.uk/thatchedproperties.php

 

[Flyfisher]

1st (insurance inspector). The existing liner is fine to use as, just need a hood.
2nd. The liner needs to be removed and insulated, and a hood installed before re-installing
3rd. They are both wrong, the liner is too small and needs to be removed completely, an open fire is fine to use without a liner.

How frustrating! Were any of them HETAS approved installers?
http://www.hetas.co.uk/about-hetas/

HETAS also has a number of advice leaflets available to download: http://www.hetas.co.uk/consumer/hetas-advice/

 

[88v8]

We have less than 6ft (1.8m for those of foreign domicile) above the ridge of the thatch, but our insurers do nag about it.

Stove.... if the liner is 5" then take it out. Few stoves are made for a 5" liner and many HETAS engineers will not connect to anything less than 6".

For thatch, the liner must be insulated. A jacket. This is to prevent heat transmission through the stack into the thatch where it can cause spontaneous combustion that will burn your house down. Reason is that a stove burns much hotter than an open fire. And even more so if you burn smokeless fuel rather than wood.

We replaced an open fire with a wood stove. We have two Clearview 500 wood stoves on 6" legs.
Wouldn't go back to an open fire.

However, if you want to go that route, either remove the liner or fit a hood. With the liner in there you're very limited as to the fire opening. Although as Paul says you can go to ten times the X-sectional area of the liner, that's still tiny. Go bigger and the fire will smoke into the room. Mind you, it may do that anyway if you're an insulation fanatic and have all the so-called 'draughts' in the house sealed up. A fire has to have air!
A hood may help with smoking, because it reduces the effective cross-sectional area of the fire opening. I presume this is an inglenook?

So for preference with an open fire take out the liner... but with no liner, the parging needs to be good. Is it? Otherwise you'll get smoke percolation through the stack.

Which brings us back to a stove.

In the end the only people you have to please are your insurers if you want insurance, and yourselves.

Ivor

 

[Loki7430]

Thank you all for the advice, it is much appreciated.

We wanted to go down the open fire route partly for the aesthetics but we were also advised that it runs much cooler so less risk of heat transfer and combustion. From what I understand from your advice is that a liner is not necessary IF the chimney is in good enough condition - I'll get the installer (or uninstaller in this case!) to give it a thorough inspection and test on removal of the liner to ensure this is the case.

I agree the height above the ridge is fairly minimal at 1m and it does limit the number of insurers but I can't see it being possible to raise it much more without significantly increasing the stack which I suppose is possible but would rather not if possible.

 

[Loki7430]

Sorry - in response to Ivor;

It probably was an Inglenook at one point but unfortunately has been rebuilt a few times to suit fashions over the years and is now a sort of half and half - it has the beam in place but a built in fireplace beneath (don't think I can post pictures yet or I would show you). In short I think the area is fine - hopefully big enough!

And yes the previous owners were not keen on drafts with secondary glazing throughout the house!! But that can be removed easily enough (between the fireplace, secondary glazing, black gloss paint on the timber and a wile list of other stuff the 80's were not kind to this place)

 

[88v8]

I think even as a newbie you can post photos via Photobucket - copy the img code and paste in the forum.

Chimney lining can be inspected with a camera. Our insurers came and inspected our flue liners by that method.
Unfortunately after 350 years the parging is likely to be quite decrepit. Still, no harm in finding out, except to your wallet.
Whether the decrepitude is deleterious, is a matter of degree. Smoke and acid percolation will further damage the pointing, and eventually you may get smoke penetration into attic or upstairs rooms.
Sometimes on old houses you can see the shadow of the flue on the outside wall where the parging has broken down and soot has percolated though the pointing.
But unlike owners in the C19 and prior, you can always go back to a liner/stove.

Bad parging is less likely to be a practical problem if the chimney draws well so smoke doesn't linger and soot (which is acidic) doesn't deposit out near the top of the stack.
Good draw needs a conservative opening ratio - as Paul said eight times is tops, six is better - and a good air supply. The air going up the chimney has to be supplied by air coming into the house, either through dedicated vents through the walls or under the floor near the fireplace, or by generalised air percolation into the house (aka draughts).

Height .... what's the stack termination? Just the stack? Or a pot? If no pot, unless the stack is very thin so there is no space for flaunching, you could increase the height easily by 2/3 ft by adding one. As we did.
Except where the stack is very special, your PO would regard it as de minimis, and not object. Many old pots on eBay.

Ivor