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I Forge Iron

Thinking a Uri Hofi side draft with charcoal forge


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Thanks, IFI and Uri for pics and notes for the side draft chimney.

The Wonderhut (16'x16', ht 12') is slowly taking shape. It's a pre-fab metal shed with steel frame and siding. I'm finishing the insulation (walls got rockwool, ceiling got something else) and then will do interior siding, do the electrical, etc., in the next few weeks provided I don't fall of the scaffolding.

I like the side draft because I just do not want to go through the roof. Roof penetrations are just asking for trouble here. But I have some questions...

Question 1: I think the side draft chimney is going to work well for my charcoal forge. Have I overlooked something regarding chimneys and charcoal? I figured I'd have to clean the stovepipe every year depending on use, but I know how to do that.

Question 2: I really like how this side draft slopes down so any rain that gets into the chimney pipe will drain out the bottom. Does it matter if I drill holes or use some kind of steel with openings as a vent at the bottom of the side draft below the chimney? Can it be removable, so when it comes time to clean the chimney I have easy access?

Question 3: Is there a thimble or some other transition piece I should use at the wall? I can't tell from the pictures. I was thinking I'd wrap the side draft in/at the wall with rockwool and use flashing interiorly and exteriorly to stop air and water intrusion, but is there a better way to do this?

Thank you for any help. Much appreciated.


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I put in a Hofi style side draft and am very pleased with it's performance. Mine is a 1/8" steel box 13" square by  4'long, poking thru the wall about 2 1/2 '. On the outside I fabbed up a simple flange and attached my 12" dia round galv duct pipe, 10 ft up to a wind turbine cap. I have a few small drain holes in the rear bottom seam and have not had any issues. On the inside I have a simple mousehole, and I made sure the opening was smaller than the area of the flue pipe. It works great, and like you said, no roof penetrations.

To answer your questions, 1)Just make sure the flue pipe is large enough- !0" would be the minimum, larger is better, and make sure it extends tall enough. I shouldn't think there are any special considerations for charcoal- I use coal.  2) I answered how I handled it  3) Where it passes thru the wall I gave the whole thing ~ 2' clearance all around from any combustible material- framing, siding, etc. I then sealed the opening up with some sheet metal- my own version of a thimble. Hope this helps.


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Our home shop has never had the pipe replaced. It's double wall 12 inch wood stove pipe for about ten feet through the roof and single wall from the hood to the stove pipe. The through the wall Hofi style that is at ESSA needed replacing after about six years, due to it rusting out. It was single wall stove pipe and they failed to put a weather head when it was installed first time.

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  • 2 months later...

I built this exact setup using galvanized chimney pipe. It corroded and fell apart after a year and a half. I've recently bit the bullet and purchased stainless pipe for this reason. 

I have holes in the back of the fabricated square tube. Any smaller than 3/8" and they plug up easily with coal dust. My holes are always open and they don't effect the draw at all. I use a long rake to occasionally clean out the back, though a little trap door might be a nice modification to allow easier access. 

To go through the wood wall I just left an inch gap all the way around. Some sort of fireproof insulation to plug up that gap would be ideal. 

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Got it, thx edennis.

Okay, as of today I have to finish the floor (sandset pavers bcz I had 'em) and do the wiring, then spend some time in the space to be sure where I think the forge should go really is where it should go. And I have to set up the other metalworking tools like my metal spinning lathe and then get confused about why I can't use it properly and ask Frosty a zillion questions about it.

If I didn't have fifty-five billion other things to do, the Hut would be done all ready. OTOH, I have remained uninjured.

Huh. Probably shouldn't have said that last bit.

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