lcb Posted May 9, 2013 Share Posted May 9, 2013 Hi guys, I would like to have a Hofi Style Chimney in my forge. I read the blueprint (http://www.iforgeiron.com/topic/23197-bp1048-side-draft-chimney/) and have a couple of questions. Is there a smoke shelf in the horizontal section or is the draft unimpeded to the flue? It's fabricated out of 3/16 sheet iron, so what might be a ballpark figure for the contruction of the horizontal section? I can take care of the flue part. Your help will be greatly appriciated. Thanks, Larry Quote Link to comment Share on other sites More sharing options...
FredW Posted May 10, 2013 Share Posted May 10, 2013 Doesn't look as though it has a smoke shelf. I am not an expert on these or any other forge style but 3/16" sheet for the tunnel seems pretty heavy. However it extends quite a way through the wall and supports the flue, so would need to be strong for that. Might consider building a super sucker side draft and just use pipe to go through the wall. It would be simpler, I think. Also it explains the tunnel is pointing slightly downward so rain will run away from the wall. As far as I know, the flue has to have a 1/4" rise per foot for proper draft though it appears to be working well. That is also code around here. That downward slope may also do the same thing as a smoke shelf as well. Fred Quote Link to comment Share on other sites More sharing options...
don schad Posted May 10, 2013 Share Posted May 10, 2013 Hi, I built one out of 3/16 diamond plate, because that is what I had. Mine is just a 12" square tube which extends about 4' through the wall. No smoke shelf. I have a 12" galvanized spiral pipe (22 g or something?) for the chimney, which fits over a circular male flange on the outside top of the square. I figure not having the edge of the spiral pipe directly exposed to the heat/fumes will prevent it from rusting away. Chimney is very light and is fully supported on the tunnel. While I agree that 3/16 is pretty heavy-duty for the chimney I theorize that once the extra mass of the tunnel gets hot it really maintains the draft. I find that this design does work very well, esp. after is has been running for a while. The lower edge of mine is about 4" over my firepot, with the end cut on a slope such that the top edge is mid-firepot or so. I am planning on raising it up a bit more as I think that it would catch more smoke during startup before the draft gets really established and provide some additional room under it. My blower might be a bit don Quote Link to comment Share on other sites More sharing options...
David Gaddis Posted May 10, 2013 Share Posted May 10, 2013 My chimney is galvanized 12 pipe too. I used it because of the almost free-standing quality. My sidedraft is 10+ in sq (near the same square inches as a 12 diameter is in square inches) . I even places a few obstacles in the throat of the side draft to experiment with. Well anyway it works. Some pics were taken at different time with different cameras. My sidedraft is about 7 feet long and is unattached to the inside of the building. When the wind blows excessively it vibrates a bit, but not too much to shake items off...as it is used as a shelf to store pencils and stuff. Quote Link to comment Share on other sites More sharing options...
Frosty Posted May 10, 2013 Share Posted May 10, 2013 No smoke shelf, no reason for one. Use reasonable gauge steel, 16ga. is overkill. the thing only needs to support itself and direct hot air and smoke. Craft paper is more than strong enough, not fireproof of course but it's strong enough to direct the smoke and exhaust gasses. Smoke shelves in vertical chimneys are there to direct hot gasses to one side of the flue so cold air trapped there won't make a dam and stop the draft all together. With a horizontal run like in the Hofi stack it acts to segregate the hot and cold air without help. That's a darned nice draft David. Well done. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Borntoolate Posted May 10, 2013 Share Posted May 10, 2013 My chimney is galvanized 12 pipe too. I used it because of the almost free-standing quality. My sidedraft is 10+ in sq (near the same square inches as a 12 diameter is in square inches) . I even places a few obstacles in the throat of the side draft to experiment with. Well anyway it works. Some pics were taken at different time with different cameras. My sidedraft is about 7 feet long and is unattached to the inside of the building. When the wind blows excessively it vibrates a bit, but not too much to shake items off...as it is used as a shelf to store pencils and stuff. Wow! That sucks! Oh, I read further... Wow! That Drafts! Quote Link to comment Share on other sites More sharing options...
Pault17 Posted May 12, 2013 Share Posted May 12, 2013 That is a beauty of a draft. The one we have at the fairgrounds' shop drafts like that when the heat is up. It actually develops a sorta rumbly roar. Very soothing when starting it up in the morning Quote Link to comment Share on other sites More sharing options...
Matt Marti Posted May 21, 2013 Share Posted May 21, 2013 Loving this style of smoke evacuation! Quote Link to comment Share on other sites More sharing options...
Humphry Posted June 1, 2013 Share Posted June 1, 2013 Anvilfire.com has a super sucker forge hood. It's what I use and it works well. I have some old 12" galv. duct pipe on it. It'll be cheap, easy to put togather and you'll like it. Just type in super sucker forge hood in your search engine, it'll take you there. happy forging. Quote Link to comment Share on other sites More sharing options...
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