Chimney Cowl

[jonk]

I have a solid fuel fire both on the boat and at home. At home I use anthracite and the fire 'exhaust' goes up a long chimney flue (two floors) into a brick chimney stack and then out via a stainless steel rotating cowl. The cowl looks like a Darth Vader helmet and is designed to always be into the wind so that the smoke from the fire is 'sucked' out. The design, I think, is based on Jetmaster fires. I find this cowl to be very efficient. Now - my boat has the traditional demountable chimney and hat which work OK BUT would a rotating cowl like I have outlined have an advantage? Would it affectively increase the flue length because of the increased suction? Any disadvantages? Has anyone tried such a cowl, I have never noticed one on a boat but I am sure it must have been tried.

 

John

[Alan de Enfield]

Apparently these turn down wind and increase the draw on the fire :

 

http://www.smokiejoes.co.uk/Smokie_Joes/Cowl.html

 

http://www.smokiejoes.co.uk/Smokie_Joes/How_It_Works.html

Edited October 7, 2011 by Alan de Enfield

[jonk]

Apparently these turn down wind and increase the draw on the fire :

 

http://www.smokiejoes.co.uk/Smokie_Joes/Cowl.html

 

http://www.smokiejoes.co.uk/Smokie_Joes/How_It_Works.html

 

Yes - those are similar to mine. Mine does not have a bird though - just a vane.

http://www.jetmaster.com.au/components/com_virtuemart/shop_image/product/Stainless_steel__4cc69ff910746.jpg

 

I think that it might help drawing narrowboat fires which by their nature have short flue lengths.

 

John

[WotEver]

Speedwheel doesn't rate them.

[jonk]

Speedwheel doesn't rate them.

 

Thanks for that link. Looks like that is a question of balance and quality? The Jetmaster type are very popular here and certainly work well. They are a bit taller than a 'normal' cowl however so that could be a problem with a boat. The vane is not above the cowl as in the 'smokie' example. The chimney does have to be upright as well so that rotation is balanced.

 

I hope this pic shows what I mean

 

http://www.canalworld.net/forums/uploads/med_gallery_8816_696_12431.png

 

John

Edited October 7, 2011 by jonk

[blackrose]

I can't see how putting any form of obstruction over a flue can increase draw, unless in this example the wind is spinning the cowl fast. If that's the case then draw wouldn't be a problem anyway - although downdraught could be and any form of cowl should help.

 

I have a Vedette cowl which also promised to increase draw. It doesn't, but it does work very well to eliminate downdraughts.

 

http://www.ebay.co.uk/itm/CHIMNEY-COWL-Vedette-Oil-Solid-Fuel-Stainless-Steel-little-used-/170708322931?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item27bf024a73

[jonk]

I can't see how putting any form of obstruction over a flue can increase draw, unless in this example the wind is spinning the cowl fast. If that's the case then draw wouldn't be a problem anyway - although downdraught could be and any form of cowl should help.

 

I have a Vedette cowl which also promised to increase draw. It doesn't, but it does work very well to eliminate downdraughts.

 

http://www.ebay.co.uk/itm/CHIMNEY-COWL-Vedette-Oil-Solid-Fuel-Stainless-Steel-little-used-/170708322931?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item27bf024a73

 

The idea is that the cowl is always facing with the wind, because the vane turns it into that position, so the air passing sucks the smoke out of the chimney while preventing any wind entering the flue. It certainly works on house chimneys but there might be other problems associated with boats.

 

John

[ditchcrawler]

I have a solid fuel fire both on the boat and at home. At home I use anthracite and the fire 'exhaust' goes up a long chimney flue (two floors) into a brick chimney stack and then out via a stainless steel rotating cowl. The cowl looks like a Darth Vader helmet and is designed to always be into the wind so that the smoke from the fire is 'sucked' out. The design, I think, is based on Jetmaster fires. I find this cowl to be very efficient. Now - my boat has the traditional demountable chimney and hat which work OK BUT would a rotating cowl like I have outlined have an advantage? Would it affectively increase the flue length because of the increased suction? Any disadvantages? Has anyone tried such a cowl, I have never noticed one on a boat but I am sure it must have been tried.

 

John

Sorry I had the wrong sort of cowl,

Edited October 7, 2011 by ditchcrawler

[blackrose]

The idea is that the cowl is always facing with the wind, because the vane turns it into that position, so the air passing sucks the smoke out of the chimney while preventing any wind entering the flue. It certainly works on house chimneys but there might be other problems associated with boats.

 

John

 

Sorry I thought the thread was about a cowl with a revolving or spinning top? Anyway, whatever the design, I don't think they actually increase draw.

Edited October 7, 2011 by blackrose

[ditchcrawler]

Sorry I thought the thread was about a cowl with a revolving or spinning top? Anyway, whatever the design, I don't think they actually increase draw.

That is what I thought which is why I had to edit my post.

[County4x4]

Anti downdraught is not the same as increased up draught. Most cowls will actually decrease the draught of the chimney in calm conditions - some like the old Brewer Aerodyne and others are designed to produce something of a venturi effect in the wind which will increase draw - but only when it's windy. There are chimney pots that will help to increase draught like the Marcone - but this is largely due to it being so tall - and of course, it would look a bit odd perched on top of your boat!

 

The rotovents are okay - but a decent one isn't cheap. Cheap ones will probably send you nuts in fairly short order as they squeak and rattle etc due to cheap bearings. I'd imagine there could be little worse on a boat with the sound of that coming down the flue pipe!

 

Andy

[blackrose]

Anti downdraught is not the same as increased up draught. Most cowls will actually decrease the draught of the chimney in calm conditions - some like the old Brewer Aerodyne and others are designed to produce something of a venturi effect in the wind which will increase draw - but only when it's windy.

 

Yes, I'd agree with that - and when it's windy most stoves will draw very well, so all you need is something to stop downdraught.

 

Personally I'd avoid anything with moving parts. It's just more stuff that can break.

Edited October 8, 2011 by blackrose

[jonk]

OK - obviously they are not used on narrowboats!

They do revolve - around a central pivot. There is nothing to go wrong with them really except wear on the bearing - but that would take many years to have any noticeable affect.

These are pictures of one:

http://www.canalworld.net/forums/uploads/med_gallery_8816_696_12431.png

http://www.jetmaster.com.au/components/com_virtuemart/shop_image/product/Stainless_steel__4cc69ff910746.jpg

 

In no wind they have no affect of course but even in a light wind they have the advantage of stopping any downdraught and/or rain entering the flue while allowing the smoke to escape downwind. I would have thought that on a moving or stationary narrowboat this could prove quite useful.

 

I have seen many references to boats having too short chimneys for full effectiveness and wondered if this sort of cowl might be at least a partial answer. Perhaps I'll have one made and see - will let you know if/when that will occur (don't hold your breath though!)

 

John

Edited October 8, 2011 by jonk