Flue/Chimney idea for 55 gallon drum forge

[torvalshank]

Hey all! 

 

I recently built a forge, and am going to be moving it inside eventually. I originally planned on using the existing 6" stovepipe that I have in the barn, but based on my reading, that won't handle the smoke from my coal forge. 

 

So I started looking at 10 and 12 inch stove pipe. After recovering from the minor heart attack that the prices gave me, I started looking for alternatives. 

 

Would something like this work for a chimney?

 

12" galvanized ducting from Lowes, $16 per 60 inches.

 

I currently have a 55 gallon drum acting as my hood, and it will have to pass through either the wall, (preferable, as there is already a hole there,) or ceiling of my shop to get outside. The shop is metal-sided, wood-studded, with foam-like insulation board between the metal and wood. What sort of insulation would I need where it passes through the wall? Additionally, would I need something OTHER than galvanized metal to sit right at the top of the forge? I don't want to gas myself out, obviously, from zinc fumes. Would the top of the upper drum get hot enough to cause that, and if so, what should I use to bridge the gap between the drum and the stovepipe. 

 

Thanks for all the answers!

[Charles R. Stevens]

With the large volume of air, the galvinised pipe should be fine, but to eer on the side of cation, you might sorce a peice of non galviniesd or a 25 gallon grease drum for the first section.

[Steve Sells]

For fire protecting for the flue, add a second layer with at least half inch air gap for where it passes through the roof line/wall to stay with in fire code too. so if you have 6 inch thick walls a 12 inch long section for a outer layer gives plenty extra exiting inside and outside the wall/roof for protection.

[torvalshank]

Here is a picture of the forge. I plan on widening the bottom of the opening in that upper barrel, so that I have better access to the fire from a wider angle. Do you think that will negatively effect the drafting abilities of the "hood," or will the 12" stovepipe pretty much take care of the draft easily enough when attached to the top of the drum?

 

 

Something similar to this, but probably not quite as far back. I will need more material than that around the bottom of the top barrel for structural reasons, as the top barrel is just resting on the bottom one, and I don't own a welder to permanently attach them. (Note: the picture below is not mine, just a random picture sources from Google.)

 

 

Also, I will try to find something non-galvanized to use as the first foot or two of the stovepipe, and a larger piece to use as a double-wall where it comes into contact with the building. 

 

Alternatively, after reading around here for awhile, would it be easier to convert the bottom half of this forge to a side-draft? Expert and in-expert opinions welcome. :) 

[Frosty]

If you open it up like the blue one it won't draw like you'd like. there are ways to do the equivalent though, how about making a section on each side of the present opening a hinged gate? That way if you need more space you can open one or both, making as large an opening as you need.

 

Yeah, we used to call that galvanized stove pipe and used it on our wood stoves for years. Steve's advice for roof penetrations is a must. You can either make one or buy a "roof jack". The open air space is left to breath, not made air tight or restrictive so air can move and cool the penetration.

 

Look around, you should be able to find black stove pipe for about the same $ and not work about getting galvy too hot. You can use header paint to encapsulate the galvy and significantly reduce the chance of it burning and producing zinc oxide smoke. Header paint is higher temp paint than stove paint, it's designed for engine exhaust headers and actually needs to get pretty hot to cure.

You can even have a forge with a pretty stack. <wink>

 

Frosty The Lucky.

[torvalshank]

Well, where I was pricing it earlier, I could get 12" black stove pipe for something over a dollar an INCH, in 20 or 24 inch sections. Whereas galvanized 12" pipe was about $16 for 5 feet. Big cost difference, around here anyway. Perhaps I'll order a piece of black stove pipe for the first few feet, and then run the rest with galvanized. Once I'm more than a couple of feet up above the forge, it should be cool enough to not burn the galvanized. Do you think?

 

Now for the life of me I cannot find where I found that price on the black stuff. Only thing I can find now is more than twice as expensive as the already exorbitant price I quoted a minute ago...reading up more on the details of zinc fumes though, it looks like they aren't given off until the galvanized piece reaches a pretty high level of heat, normally only achieved by welding or similar activities. If that is true, then using some of it in a well ventilated area 4 or 5 feet above the fire should be ok, at least until the building catches fire. At that point though, I'm leaving anyway, zinc or no zinc.

 

My only other question is to where I should vent this thing out of. My shop already has a hole high up on one wall, where a six-inch pipe went out. Could I use an angle or two to be able to utilize the existing hole, (although I will have to enlarge it,) or will I have to punch a hole in my roof as well? And how would you recommend I seal said hole if I'm putting it on the roof of my metal-roofed building? Some sort of caulking material or something? 

 

Thanks so much for all the help. :) 

[Glenn]

I have found that keeping the opening to the fire as small as possible helps greatly. My current opening is 4 inches below the 2nd ring and 10 inches either side of the center line. This is for a standard 3 ring drum. I also use an arch at the top of the opening to cut the corners and create a smaller opening area. This would seem small to some, but as long as the metal can be put inside the door ..... YMMV.  If you are doing large pieces you will need to be at a larger forge. No one said you could have only one forge  :)

 

You can find 14 inch pipe on the inside of some small water heaters. Other sizes are 16 in and 18 inch pipe for the larger heaters. You can then reduce to the purchased pipe size.

 

Something to consider,

Look at the opening on the black drum as compared to the chimney size. It wants to suck air in and move the smoke and air up the chimney. Now look at the opening on the blue drum as compared to the chimney size. It is trying to suck in all the air needed from outside the forge area. This leaves only a limited amount of room for the smoke to be removed and sent up the chimney. Do some math (did I say that) and compare square inches of chimney to square inches of opening.  I have found that opening area vs chimney area being equal works well for me.

[Frosty]

I'd go with the galvy pipe, especially for that price difference. A lot of folk are really sensitive about getting zinc anywhere near heat, a little too sensitive. You're absolutely right zinc doesn't start to burn till mid orange heat, above proper brazing temps by a good bit. You're right, if a person's forge stack is getting that hot, the smith is standing outside waiting for the FD to come put the shop out so no worries about zinc smoke.

 

There ARE folk who are sensitive to zinc exposure and should take precautions but it's not too common, like genuine gluten allergies. Zinc is a necessary nutrient, without it we wouldn't live all that long. Bear in mind breathing zinc oxide is a BAD thing in almost any quantity.

 

Frosty The Lucky.

[EricJergensen]

Zinc melting point: 787.2°F (419.5°C)

zinc boiling point: 1,665°F (907°C)

 

Until it melts, it's protected from further oxidization by a thin oxide layer. Even then, there isn't much in the way of vapor so you don't have airborne zinc oxide. Somewhere between the melting and boiling point, it starts getting dangerous. At boiling all you-know-what breaks loose, but, like Frosty says, you've left by then...

 

I spent a fortune on black pipe in my first go. Wish I hadn't. It never gets anywhere close to 787°F in use.

[torvalshank]

Ok. Thank you all for the advice. I think I'm going to go with the 12" galvanized then, when I go to install this permanently in my shop. For now though, I will continue to drag it outside when I want to use it. The chimney can come in a few months, before winter hits. And I may leave the opening this size for now, rather than enlarging it. 

 

My next quest is a cheap source of refractory; the brake rotor being used as a firepot sits about half an inch up above the top of the drum, and I would like to line the rest of the drum with enough refractory to level it out with that, and give me a bigger working surface. 

 

Going to be researching DIY solutions for that later today. Thanks all for the help. :) 

[Glenn]

Use mud or let the gap fill with ash. 

[torvalshank]

I'd like something hard enough to let me move coal around on it with the scraper, so I can manage my fire better. So I think the ash is probably out. Any kind of mud in particular, or just muddy mud? 

[Glenn]

You need high quality mud,

 

I had to get a shovel and bucket, and travel all the way to the back yard to obtain my mud.  Always ask the property owner (read wife) where she would like a hole planted. (grin) Sift out the rocks and keep it moist, not wet, when applying to the forge. It will crack as it dries.  Mix up a bit of slurry and fill the cracks as needed.

[torvalshank]

Got it. High-quality Grade-A backyard mud. From only the finest of backyards. ;) 

[Frosty]

Not to take issue here but the finest throwing dirt clod, dirt is the best. Just wet enough to make a good hard lump to throw at the mean neighbor kid that just hit you with one.

 

NOT to be confused with the dirty clods our wives often mistake us for when she discovers our clay mine in the far corner of the garden.

 

Frosty The Lucky.

[torvalshank]

With 34 acres, I can hide my clay mine VERY well. ;) 

As for the original topic of this thread, I have also talked it over with a local smith, (in addition to you fine gentlemen,) and he is going to give me a hand putting in the chimney later this summer, before it gets cold.

 

Otherwise, I am just practicing away. Maybe one day I'll make something pretty enough to take a picture of. ;) 

 

Thank you all for your help. 

[LastRonin]

Hello fellow Hoosier ( I live in Bama now but was born near Loogootee).