[Stoves] Stack question

Frank Shields franke at cruzio.com
Sun Jun 4 23:40:02 CDT 2017


Thanks - I was looking at a pot belly stove with a long stack that had a hole about three quarters way up and smoke was coming out. Seemed that should have not have happened. 

Frank 





> On Jun 4, 2017, at 6:41 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Frank
> 
> There is another option which is often used in fireplaces. You can have a fan that works as an eductor (ejector). It pushes air into the top of a chimney and out, creating a draft below. The gases from the fire do not pass through the fan.
> 
> This is sometimes used to start masonry heaters with downdrafting in their gas paths, where there is no bypass. If the fire is lit the stove is too cold to let any heat get to the vertical chimney so the fan is turned on until there is enough heat to operate the chimney. When the system heats up the fan can be turned off.
> 
> There are small stoves that work like that. Didn't the World Stove work that way for drafting the central hot gases down through the fuel bed without adding oxygen? Maybe someone can remind us.
> 
> There are gas cells that work the same way. The original equipment set at the SeTAR Centre used industrial gas measurement cells where the gases were pulled through from the source without a pump. Compressed air was allowed to flow into an eductor and this created a strong vacuum in the outlet pipe, pulling the sample through from the chimney. Such equipment is available from California Analytical Instruments http://www.gasanalyzers.com 
> 
> One company that makes this sort of thing is http://croll.com/process-powered-ejector-systems/
> 
> The advantage of such a system is that you don't have to worry about and clean a pump. Compressed air can be from any available source. For a chimney, passing the hot gases through a fan can destroy it. Blowing air into a stove is dangerous from a wear-and-tear point of view. As a general rule stoves including heating stoves should have a negative pressure in them at all times so that any leak pulls air in, not pushes smoke out.
> 
> Robert van der Plas and I considered making this a requirement of the Mongolian National Standard year ago when it became obvious that the draft control on some of the 'improved stoves' was limiting the draft not limiting air entry into the stove. If a child pushes the damper in all the way blocking the chimney, everyone dies. 
> 
> The text has to be framed in a way that allows innovation but prevents mis-operation. Some jurisdictions have a requirement that only a certain % of the chimney area can be closed when the damper is fully 'in'.
> 
> An eductor can be used to pull preheated air into the secondary jets without pressurizing the heating chamber. Turning it off sort of works like a damper.
> 
> There are many ways to set a fire!
> Crispin
> 
> 
> 
> Just wondering…
> 
> If you have a fan at the bottom blowing air into a stove and have a leak in the stack smoke goes out into the room.
> If you have the fan at the top sucking air up and have a leak in the stack no smoke goes into the room. 
> 
> What happens if you have natural draft in the stack? A hole in the stack will let smoke into the room or will room air be sucked into the stack?
> 
> 
> Thanks
> 
> Frank
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Thanks

Frank
Frank Shields
Gabilan Laboratory
Keith Day Company, Inc.
1091 Madison Lane
Salinas, CA  93907
(831) 246-0417 cell
(831) 771-0126 office
fShields at keithdaycompany.com



franke at cruzio.com







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