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Permanent Forge Chimney


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The shell of my new shop is nearing completion... we'll probably start on the standing seam roof later this coming week(using the tools we made!). I now have to actually think about setting up the forge. I do not want to go through the roof. The forge will be against the end wall and I expect to put the chimney on the outside, extending above the roof line. The chimney will have to be over 20' high. Sooo....
I'm interested in recommendations. The current direction of my line of thinking is standard block chimney with standard flue liner, with a 'T' for the forge duct. It means two right angles, but should still draw if its big enough. I'll post pictures of what I'm facing soon (if we can still do that).

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You may want to make a provision for adding a booster fan in case it's necessary -- sounds like you could do this by using a tee instead of an elbow on one of these right angles. You may also want to think about using 45 degree angles instead of 90s -- I don't know what your setup is like, exactly, so I don't know if that advice is worth anything or not :)

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I recall from somewhere that a 90* bend in a flue cuts down the draft up to 20% for each 90* (Don't hold me to that till I can point you to a reference.) The horizontal distance between 90* bends should be keep it as short as possible.

JJ (James Joyce from Calif) would be a good person to ask about this.

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Ed

Congratulations on the building of your shop. There is an advantage to having an interior flue. It will be warmer and draw much better in the winter, of course it will also warm your shop in the summer too.

Anvillain

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Hmm -- what I would do is cut an oval hole in the wall where I was going to put the forge (I would be likely to put it in the middle of the gravel area to make heats on bar centers easy...), put one 45 degree elbow on the hood itself (definitely side draft), put a few feet of duct on the elbow til it makes it outside, and use a second 45 degree elbow to shoot the chimney straight up. If this doesn't make sense, let me know and I'll draw something and post it :)

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now you have choked us all with the pic of your new shop,and shook me into reroofing the big hammer shed after 30 years of rusting,


you should go all the way and make a brickwork chimmney brest and stack ,and then a smart brickwork forge with brick arch and canopy it would make a great focal point to a splendid job ,

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I agree with Bruce... :)

With regards to the two 45s, you're going to have the potential for problems anywhere you have a wall penetration... that's life, unfortunately. I don't know what you're sheathing with, but I'd say, apply loads of silicone caulk and forget about it unless you have a problem. Of course, I'm no expert. :wink:

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Why not put a window in the wall. Then put a side draft hood in the window.

The side draft hood could sit outside the shop and the forge inside the shop. IF you ever got out of blacksmithing, you could finally install the window in the wall. :)

How ever it is done, make provisions for getting long pieces, or odd shaped metal to the fire. May want a jib crane handy to the fire if you work big stock.

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Ed,

My first shop had an overhead hood that was attached to a 12 inch round duct that made a 90 out the wall and then a 90 up. The horiz piece was 6 feet long and the vertical was 8 feet, which put it a foot or so over the peak of the roof. Although it was better than nothing, it still smoked a lot and I finally went to a straight stack.

For your shop, I like Swamp Fox's idea of a window that you can set a side draft chimney in. It's very versatile if you decide to move something later. I just don't think you will like the performance of two bends in the chimney.

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just becareful of the radiant heat from the stack. The first few feet of my 10" stack can get so hot that it'll burn your hand like a grid iron. if that was going through flammables, I'd have at least 2" of surrounding moving ambient air to keep things cool. The hood gets just as hot. Wouldn't want to burn such a pretty place down. BTW, what type and size of forge are you putting in.

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Bruce: If I weren't in such a danged hurry to get back up and running, I'd do exactly that. I'd hoped to build the shop from stone, since rock is free and plentiful all around me... but realized that when I'd be done at 120 years old, I probably would be too near retirement to use it much. I haven't ruled out a stone forge, but it will have to wait. I like working stone.

NOW you guys recommend the window! :) Note that I already placed them toward the sides of the end wall... not in the middle for the very express purpose of putting a chimney there.

Hollis, the side draft sounds good to me, except that I don't see how to incorporate that so far above the forge.

One way to use the pair of 45

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Ed,
You do know what you have to do.
Go through the roof, directly above the forge. No bends elbows etc.
If you go through the wall, window, all your doing is trading one problem for 3 or 4 others.

Nice looking shop. It has me jealous :D

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Ditto what Jim said, through the roof. I would not recommend the window. Having no bends in my system I am very glad for that. I can stir that fire up and not have to worry about waiting for the stack gas velocity to get up to speed before laying on the air blast. I think that the window would work ok if it was down low near normal forge working level, so long as you ran enough stack to get well clear of that roofline (or stuck a fan in there). As you already aluded to, put the stack up near the peak, so the roof jack is just a few inches below the peak. Caulk the heck out of it and you wont have any leaks (when laying the roof jack, put a couple of beads of caulk on the underside so that it creates a seal between the metal jack and the roof plywood / OSB. That's how I did mine and I am using a shake roof, so it got a bit complicated cutting some of the peices to fill in all the voids, but still not a leak. (Not to mention that you have one up on me already because your roof isn't on yet, I had to peel off a bunch of shakes to lay that jack down good and solid.)


Ed, you have got more guts... er faith than me, I don't think I'd be able to sleep wondering if ther was a spark that was going to light the horse barn on fire in the middle of the night. Even as it is, every night after shutting down the forge I turn off all of the lights and go wandering around the forge area looking for glowing embers that have fallen against the walls etc.

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Ed, The new shop looks like it will be really nice. I like the way youv'e minimized it's apparent height by building into the bank.

Since I rent my shop space I am not able to cut a nice big hole in the roof for a stack and had to use an existing flue. I am working with a six inch stove pipe running vertically from a side draft hood for about eighteen inches. It then makes a bend a little less than forty five and continues for another three feet where it bends again to enter an induced draft fan which was originally intended for a large gas fired hot tub heater. I'm using a Centaur fire pot and tend to build fairly large fires. I haven't had any problems with removing almost all of the smoke with this setup. Sometimes drafts elswhere in the shop can waft a little smoke into the other shop areas. You do have to put up with the motor noise though. If you decide you need an inducer I'd try to find one you could mount outside. That said- if it was me I'd be going sttraight up and out the roof if I could.

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Ed,

What I had in mind was to fabricate a side draft box and set it in the window. It could also be insulated at that time and flashed for drip-proofing. The duct would run up the outside of the wall and either cut straight thru the overhang or dogleg to clear the roof. The forge is then right up against the wall or nearly so. The only thing you have to get used to is that you have no room behind but I have seen a couple forges built this way and the smith was not having any trouble. My side draft chimney is only about a foot from the wall and you cannot walk behind the forge. I have some miscellaneous stuff stored there but the proximity to the wall is not a problem and it keeps the center of the shop clear so I can clutter it with other stuff. :lol:

BTW - you probably already know this but use at least 12" round for the duct. 10" is marginal and anything smaller will smoke some. I had a buddy of mine make me a nearly 12" square duct from a piece of 4x8 galvanized and it worked quite well (until a storm took it off one day). He bent it on a brake and folded up the sides then made a seam where two corners met. Easy and fast for an HVAC guy to make.

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Maybe I'm just lucky but 10" works great for me and I have a pretty big firepot. It is straight-up with no bends and smooth a glass, so maybe that helps it. For me, 10" was a critical size because a 12" roof jack costs about $130cdn and up while a 10" was only about $55cdn. That's half a tonne of coal difference! :shock:

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JimG: I'll check on some roof exhaust options. A good friend has already done his with a commercial package and is happy with it. But it was at a pretty stiff cost and he only had to go a fraction of the height I'm facing.

Stephan P: I checked with my brother (he's doing most of the construction -- I just do as I'm told) and he seemed to think it would be just as easy to install the roof and then cut the penetration if I decide to go that route. You are kind in your choice of adjectives to describe my behavior in housing animals, hay, torching and forgework all in the same homebuilt pole barn. I had to get rid of the horses when I quit work to do forging and goofing full time, so it hasn't been QUITE the fire hazard it once was. But the 4' concrete knee wall was mostly because I'm tired of having to be SO worried all the time.

SGensh: Thanks. The bank was there first. :D I do hope to avoid the auxiliary exhausting fan. I never like the noise they make either, in the shops I visit that have them.

Hollis: I am going to look into your design suggestion. It is sort of a hybrid solution that might be the ticket. As you say... I don't need to go behind the forge... I haven't done that for years.

John Larson: I didn't think of that, but you are right! Of course now I'll have to put a weathervane on top of it... hmmm.... this could take awhile...

Steve K & Stephan P: Thanks. I've got more to think about now, obviously. I appreciate it.

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My shop is a metal building/roof with plastic covered insulation. Due to the insulation, I wanted to use triple walled flue pipe and I also wanted to use stainless steel. The only size I could find locally was 8". I ran it straight up from the sidedraft hood. I have to be careful and start my fire slowly but once the air in the flue warms up, it draws very well. I can forge all day and the outside never gets warm. I did not even have to build any kind of box for a stand off where it goes through the roof.

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Just my humble opinion. a first class flashing for your roof can be made by a competent HVAC contractor (or might be purchased commercially made). I made mine but it takes a little maint. to keep it up. Just a piece of glavanized with an oval cut in it at proper size. I use a piece of auger pipe through this oval (which is cut to fit tight up against the pipe). I use Black Jack at the place where the leak will be. Will be 3 years since I have crawled up to re-seal it. In reality, a flashed/collared vent pipe entrance would have been better but you know how it goes when you need it late of an evening on Saturday night. This flu pipe is 8" and should be minimum 10" . The flu comes from the roof down to the ceiling joists (which I note in your pics are plentiful) and sets in the center cavity between 2 joists. I have a small amount of decking on top of the joists at the place where the flu rests. I cut a generous hole in the decking and now we have a place that is free of heat radiation for the flu to set. The flu (which ain't light) has 3 pieces of 3/8 x 1 (or mebbe a little wider) anchored to it and these 3 pieces of bar are bent at 90

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