[TheForge] flues -- Shot Gun Top

[williamsiron at comcast.net]

Dave & others,

ABANA has a Coal Forge Handbook edited by Stephen Maghee that includes the "Shot Gun" design of rain cap. I think it's called the no-loss cap.

Mark Williams
Snow Hill, Maryland

-------------- Original message -------------- 
From: "David E. Smucker" <davesmucker at hotmail.com> 

> Rain never falls straight down -- or at least a heavy rain never falls 
> straight down -- always at some angle to the vertical. This depends on the 
> amount of wind. Because of this it is possible to put a somewhat larger 
> section of pipe / flue at the top of your stack so that it has a small 
> clearance at the bottom to let water drain out above where the main flue 
> enters your roof. In my case with a 15 inch flue I have an extension on the 
> flue that is about 15 and 1/2 inches in dia. and extends 60 inches above the 
> top of the flue itself. It is shimmed out from the main flue by 1/4 inch 
> shims so that there is a 1/4 gap all around the main flue. The two section 
> over lap by 12 inches. Rain falling (or snow) at an angle hits the side of 
> this "shot gun" extension and run down the inside of the extension and 
> drains out in the gap between the two flue sections. Rule of thumb is that 
> the extension above the main flue should be 4 times the diameter of the main 
> flue. In my case 4 x 15 equals 60 inches. 
> 
> This is a common industrial design today, but not really new -- some clay 
> chimney pots in England were made this way with a ridge (rim) on the inside 
> and drain holes. 
> 
> Does it work? Not perfect, in a light rain I do sometimes get a little 
> water down the flue but less than I get from condensation when starting a 
> fire with a cold stack. But I have very very good draft. Keep in mind that 
> the common cone hat at the top of the stack is a very bad draft waster -- 
> most studies say it cut the draft by about 50 %. (Depends on how much 
> separation between the cone and the flue. My biggest surprise is that it 
> works best with heavy rain, heavy rain seems to always come with more wind, 
> and therefore more angle to the vertical. 
> 
> I don't have spark screen, but I do have a 20 foot stack (without the shot 
> gun extension) and I am burning coal, not charcoal. (Charcoal and some 
> woods are bad for carrying glowing embers up the stack.) 
> 
> I was going to do an article on this type of stack for the AACB Newsletter, 
> but I retired (burned out) before I got it done. May do one in the future, 
> as it is getting time to do some more articles. 
> 
> Dave Smucker 
> Brasstown, NC 
> 
> ----- Original Message ----- 
> From: "GRAF" 
> To: "Sponsored by ABANA" 
> Sent: Thursday, January 17, 2008 5:36 PM 
> Subject: Re: [TheForge] flues 
> 
> 
> > 
> > davesmucker at hotmail.com wrote: 
> > 
> > "culvert with a shot gun top." 
> > 
> > I think I know what you mean. but please explain anyway. 
> > 
> > Mike Graf 
> > _______________________________________________