Hw do I align a chimney cowl?

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Hw do I align a chimney cowl?

Postby Crickleymal » Sat Nov 10, 2012 12:20 pm

We're installing a woodburning stove and I've got to put a chimney pot and cowl up as we don't have one. I've bought a bonnet cowl like this http://www.wtknowles.co.uk/products/pro ... =&styleID= but nowhere can I find out how to align it.

Should it go in line with the prevailing wind or across it? And does it even matter?
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Re: Hw do I align a chimney cowl?

Postby merlin » Sat Nov 10, 2012 12:35 pm

I have just had a look out, everybody here has a solid fuel, wood or coal, or both. Of the people that have the one you have, they are set in all driections. I don't suppose that is help, but is seriously doubt that anybody has any problems.
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Re: Hw do I align a chimney cowl?

Postby Odsox » Sat Nov 10, 2012 1:47 pm

Bearing in mind my tag line ... a chimney works by the wind blowing across the end of a pipe (as well as heat rising) in the same way as a spray gun or a carburettor. If the wind blows across the ends it should work and if the wind blows through the middle it should work, so I would say that it doesn't matter at all which way you align it.
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Re: Hw do I align a chimney cowl?

Postby oldjerry » Sat Nov 10, 2012 3:08 pm

If you're talking about one of those T-shaped jobs,I'd say if you are exposed and windy(yes,I'm talking about your house) then I'd have it shielded from the wind,and the converse if you live in a cosy Dingley Dell.On the other hand if your woodburner roars away/won't draw get back up that rickety ladder and adjust.Bws.
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Re: Hw do I align a chimney cowl?

Postby marshlander » Sat Nov 10, 2012 11:02 pm

Chimney cowls used on redundant flues are usually a mushroom shape or bonnet hood. This type of chimney cowl is only used to provide flue ventilation in an unused chimney and should NEVER be used on a live chimney. If you bought this on the advice of a builders merchant they should be shot!

Put up the tallest pot you reasonably can, the tapering towards the top "pulls" the air up from the fireplace or woodstove increasing draft. Make sure the diameter of the base of the pot suits the size of the flue ie not smaller. If you have more than one pot make them the same size or the second pot can syphon the first.

We're on the North Lincolnshire coast (always windy) and had to rebuild the chimneys when we moved in. We installed 3ft tall pots( a roll top and a bishop) and only very rarely have any problems.

Most of the so called down draught cowls are useless anyway. Some fancy terminals have a good reputation for working but their success is just as likely to be added height as their complicated design IMO. Cowls only work if your fireplace smokes when the wind blows in which case a spinning cowl may help. Most other problems are causes by too short a stack or wrong sized flue.

(My job in the real world included designing flues)
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Re: Hw do I align a chimney cowl?

Postby marshlander » Sat Nov 10, 2012 11:12 pm

btw are you using a flue liner with the stove in which case you can sweep through the stove. If not you will need access to the chimney breast to remove soot once it's been swept. I prefer a soot door fitted on the outside of the chimney stack.
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Re: Hw do I align a chimney cowl?

Postby Crickleymal » Mon Nov 12, 2012 9:06 am

marshlander wrote:Chimney cowls used on redundant flues are usually a mushroom shape or bonnet hood. This type of chimney cowl is only used to provide flue ventilation in an unused chimney and should NEVER be used on a live chimney. If you bought this on the advice of a builders merchant they should be shot!

No we bought it cos it would do the job. Why can't it be used? It provides plenty of area for the smoke to escape.

The flue is already concrete lined according to the HETAS registered bloke who is doing the installation.
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Re: Hw do I align a chimney cowl?

Postby GeorgeSalt » Mon Nov 12, 2012 10:39 am

Is that the exact cowl you've bought, or just one that looks a bit like it?

It very clearly says "Suitability : Redundant Flue" on the page you linked to.
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Re: Hw do I align a chimney cowl?

Postby Crickleymal » Mon Nov 12, 2012 11:48 am

GeorgeSalt wrote:Is that the exact cowl you've bought, or just one that looks a bit like it?

It very clearly says "Suitability : Redundant Flue" on the page you linked to.


One that looks like it. I've seen plenty of these sort of cowls on chimneys before so I assumed that they would be ok. Looks like I made a mistake. I still don't see what's wrong with them and Merlin's post indicates they are in use round that neck of the woods.
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Re: Hw do I align a chimney cowl?

Postby marshlander » Mon Nov 12, 2012 1:17 pm

You may find this pdf useful reading http://www.solidfuel.co.uk/pdfs/curing_ ... oblems.pdf

Are you fitting a cowl due to problems in the past? - your stove may well work perfectly without one.
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Re: Hw do I align a chimney cowl?

Postby Crickleymal » Mon Nov 12, 2012 3:10 pm

No, only to stop rain coming down and rusting the stove. I can easily make one like this http://www.chimneycowlproducts.co.uk/ac ... xing_.html
I bought the ceramic one because it fitted the pot that I was buying and it was there. Cash flow problems may mean I can't afford to get another one.
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Re: Hw do I align a chimney cowl?

Postby boboff » Mon Nov 12, 2012 3:46 pm

Hi Mal.

I had a cowl on my chimney with a Woodburner attached, and knocked it off two years ago, and I have noticed no discernable change in draw, or problems with rain and rusting what so ever.
Given your budget try and take the redundant flue one back and don't bother to replace and cop the cash ( Thanks Marshlander that was great advice by the way, who knew?....well you, but not me)

The thing I think is so important is sealing up all the joins well from stove to flue, I bought Fire cement in a "silicome" style tube this year, and it works really well, then go over the top of it with the flexible black heat resistant silicone..... This and ropes on doors do more to make a good fire crap or a crap fire good in terms of burn I have found...
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Re: Hw do I align a chimney cowl?

Postby GeorgeSalt » Mon Nov 12, 2012 5:39 pm

Crickleymal wrote:No, only to stop rain coming down and rusting the stove. I can easily make one like this http://www.chimneycowlproducts.co.uk/ac ... xing_.html
I bought the ceramic one because it fitted the pot that I was buying and it was there. Cash flow problems may mean I can't afford to get another one.


It doesn't mean that the pot you bught can't be used, but you need to check on the manufacturers specifications for that cowl. Not just one that looks a bit like it.

Standard cap for a woodburner installation in the UK is a simple (and cheap) zinc cap with birdmesh round the sides. Can you return the cowl you bought, if it turns out not to be suitable?
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Re: Hw do I align a chimney cowl?

Postby Odsox » Mon Nov 12, 2012 6:06 pm

GeorgeSalt wrote:Standard cap for a woodburner installation in the UK is a simple (and cheap) zinc cap with birdmesh round the sides

That's exactly what I have, although mine is stainless steel.
However, the only reason I got one was to stop the wind roaring, it literally made it difficult to hold a conversation or listen to TV in stormy weather. Before that it was just a standard open pot and although logic says that rain will pour down the chimney, I never noticed any problems with damp or wet. I think the soot absorbs the raindrops and the updraft dries the soot.
It was open for several years without problem, so I'm not sure you actually need a cowl at all Mal.
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Re: Hw do I align a chimney cowl?

Postby Crickleymal » Mon Nov 12, 2012 7:36 pm

Ok thanks everyone. We'll see if they'll take it back. Trouble is we noticed a chip out of it when we got it home :angryfire: (carefully transported on the back seat of the car so it wasn't us) so whether they'll take it back I don't know. I'll get SWMBO to go over tomorrow and ask them about suitability. They are a builder's merchants though rather than a stove supplier or chimney sweep.
Malc

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