Tom Roberts Posted June 21, 2006 Share Posted June 21, 2006 I'm hoping someone can help me out. I'm moving my shop into my pole barn - finally. I need to set up a hood and chimney for my rivet forge. The forge is about 24"x30" cast iron with a small hand crank blower (1 1/4" or 1 1/2" diameter discharge). I plan on fabricating a hood and chimney directly above my forge. Currently, I'm planning on using a 10" diameter chimney. Is this too large for my small forge? If possible, I would like basic dimensions or good design features (like what volume of exhaust air should my hood be designed to, etc.). Also, I would like any details or information regarding the chimney penetration through the roof. Do I need to break down and buy expensive class A chimney pipe? Or can I make my own double wall insulated pipe (hopefully so!) Also, I would like to know how I should flash the chimney penetration, etc. and anything else useful you can share regarding this topic. To get a better picture of what I'm working to, my barn has open wood trusses on 24" centers. The bottom of trusses are 10' above the floor. The roof peak is 15'. Currently, I plan on extending my chimney approximately 2' above the peak. Any help you can give me would be greatly appreciated. Thanks! ~ Tom Quote Link to comment Share on other sites More sharing options...
irnsrgn Posted June 21, 2006 Share Posted June 21, 2006 you would probably be better off with a side draft chimney, it will function better than a hood. and 10 inches is about right.http://www.iforgeiron.com/Blueprints/BP0046Fire_and_Smoke_05/BP-0046Fire_and_Smoke_05.htm Quote Link to comment Share on other sites More sharing options...
rthibeau Posted June 21, 2006 Share Posted June 21, 2006 If your roof is wood, a Class A chimney kit is the safest and probably the easiest. A metal roof might take a double chimney with proper clearances. A 10" chimney is good although a 12" might give a better draft with a shorter chimney height - rule of thumb is top of stack 2' above roofing within 8' radius. Depends on prevailing winds and chimney orientation to them. If the roof shelters the chimney from the wind, it needs to be higher. My trusses are 24" on center, the stovepipe goes in the middle between two, and I have a piece of sheet metal attached to each truss on the side to reflect heat. Works good. Standard flashing to prevent leaks in the roof and brace the chimney. Most would agree with Irnsgn that a side draft is better than a hood. Quote Link to comment Share on other sites More sharing options...
henerythe8th Posted June 22, 2006 Share Posted June 22, 2006 What sort of roof material do you have? Is there a plywood or other wooden deck below the roofing material? It can be a real PITA to get a seal if you are penetrating a metal roof (eg. delta rib form), but I found a great product that will get you there. It is a rubber flashing with a dead soft aluminum banding around the edge that can be formed over the ridges and through the valleys. Your safest bet is to probably use a graded chimney system with support box from your "ceiling" on up. That diameter is likely going to be expensive... My 2 cents... I can probably find more info if you need it. Let me know... Quote Link to comment Share on other sites More sharing options...
stryder Posted June 22, 2006 Share Posted June 22, 2006 Tom, hi, i agree with irnsrgn on the side draft. i was a certified chimney sweep for 18 years, the code on solid fuel vents is 3' above the roofline, or 2' above anything within 10'. (sorry rthibeau !) i would get a ceiling support kit (it supports the chimney weight and adapts single wall to double wall) and go up from the bottom of the rafter. class A pipe needs 2" clearance to combustibles. flashing, storm collar, and cap. some systems void the warranty if all applicable parts aren't in said system, so read the fine print! i have seen the seals henrythe8th was talking about and they are it for metal roofing, i would trim the silicone seal back about an inch and put the storm collar on over it. this type of system saves the most money as a thru the wall system requires so much more class A , and various parts. also look for 316 alloy which is resistant to coal soot and the acids that form inside. a good resource is Copperfield Chimney Supply, out of Fairfield Iowa. www.copperfield.com good luck and i hope this helps. George Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted June 22, 2006 Share Posted June 22, 2006 Doesn't show too well from this angle but the tips of the flames are making a right angle turn into the stack. This is an old material hopper turned upside down and the "bottom" cut out to clear the stack, which is a piece of galvanized 12" round duct (not visible in this pic). Some folks say galvanized is bad to use but I think it is far enough away from the fire (too warm to touch with a bare hand but not nearly hot enough to make oil smoke). Using galvanized right next the fire might generate some fumes but I just don't know... This forge is in a pole barn with a 12 foot shed roof and the chimney is on the high side, with about 2 feet protruding. If I had a barn such as you describe, I would run two pieces of angle iron across two trusses and box in the stack, then go right thru the roof. Seal with plain flashing and plenty of tar, followed by a "coolie hat" on top. Such a chimney will likely pull most of the smoke and ash with no problem. Quote Link to comment Share on other sites More sharing options...
Chris Pook Posted June 22, 2006 Share Posted June 22, 2006 Good thread, I'm going to be putting the chimney in the new shop in the next couple weeks. I bought some insulated chimney pipe at a used building supply store for real cheap, I'm sure you could find some in your area. What is everyone running for caps on there chimneys? I have an typical ashpalt shingle sloped roof. Quote Link to comment Share on other sites More sharing options...
Tom Roberts Posted June 22, 2006 Author Share Posted June 22, 2006 Thanks everyone for your great advice and nice photos! I appreciate all the effort! I've reconsidered and will fab a side draft chimney. I need to get my blower moved around though (it bolts to my forge). 'Cause my set up right now appears to be backwards. Maybe my forge was built for a lefty. Quote Link to comment Share on other sites More sharing options...
Rick Barter Posted June 22, 2006 Share Posted June 22, 2006 All: Very HOT ( pun intended ) topic it seems. I, too, have to get my chimney set up in my barn. My goal is to do it before winter. I have some questions: I have a metal roofing on my barn, but it has humps in it. How do I know to get the right flashing/kit/whatever for it? Also, because of said metal roof, what is the best way to cut through it and the batting on the underside of it? Thanks, rvb Quote Link to comment Share on other sites More sharing options...
henerythe8th Posted June 23, 2006 Share Posted June 23, 2006 Rick & others, Check out McMaster-Carr item 7503T5. This is NOT the only place to buy these, but convenient for web search sake. If you place 'mcmaster' in a search or url line you'll get their page then search for that part number, you'll see what I was talking about before. I found what I needed at the local woodstove shop when I inquired re: metal roof... I think the one that I have is black, McM says theirs is grey... as far as the hole is concerned--tin snips, sawzall, plasma cutter? easy on the plaz, likely a pain to pack up there anyway, hah! Your "batting" is just fiberglass with a layer of plastic, eh?--razor knife or scissors... Be aware that most of this "stuff" is heat sensitive, except that fiberglass insulation, and that you need to isolate that heat or risk fire. Keep in mind that the base of that rubber flashing is going to "shrink" when you form it over the ridges in your roof "tin" and keep that hole as small as practical. As stryder says--it's best to get the support kit and graded/cert'd pipe from the rafter/ceiling level up. Likely, you'll locate the support box and go up from there. Easiest to use a plumb bob from the bottom of the roof down to the center of the support, mark, then punch a screw, ice pick, awl, etc UP through the roof. Go up there and then layout and cut from above. Remember that even a slight pitch on a metal roof can be SLICK. A bit of dust and or oxidized paint on that metal and you have a slip and side with a NASTY ENDING.:cry: I've thought of placing a "normal" metal flashing over the rubber one to protect it but we have some heavy wind around here sometimes and I'm afraid it might make matters worse... Don't mean to ramble, Henry Quote Link to comment Share on other sites More sharing options...
Rick Barter Posted June 23, 2006 Share Posted June 23, 2006 Not rambling. GREAT INFORMATION! I'm a newbie to cutting holes in roofs and want to do this right the first time! With regards to copperfield.com...they only sell to folks in the industry it seems. I'll search as HenryVIII said. I reckon that if I go to a building supply or home center place they can guide me, no? What would I be looking for in ways of support kits and flashing? Any special terms there I should search for? Thanks to all that help. This forum is the best! rvb Quote Link to comment Share on other sites More sharing options...
oakwoodforge Posted June 23, 2006 Share Posted June 23, 2006 A little trick I learned for starting holes in the middle of a sheet of tin roofing. Take a large flat blade screwdriver with sharp edges place one edge of the tip on the tin, strike with a hammer to open a hole then use righthand or lefthand snips to trim to size. By the way if someone needs anything from Copperfield I can always pick it up for you, they are just down the street from my slavage-yard aka Day Job. Jens Quote Link to comment Share on other sites More sharing options...
Rick Barter Posted June 27, 2006 Share Posted June 27, 2006 Well, I've got a 4:12 pitch on the barn roof. I've got a source for the stovepipe and will be ordering what I need as soon as I determine WHERE in the barn I'm going to put the forge and how much pipe I'll need. There are two possible places I've identified. I'm trying to "see" what it would be like at either place. My only problem is how big the hole will have to be for 12" I.D. class A triple lined stovepipe. I'll have to check with the stove company to see what the O.D. is. As it is, the cross pieces (that run perpendicular to the trusses) have 19.5" between them. I don't know if this will be enough for 12" I.D. No real question here I guess. Just rambling to y'all. rvb Quote Link to comment Share on other sites More sharing options...
stryder Posted June 27, 2006 Share Posted June 27, 2006 Rick, you should be good with 19.5 inches, pipe should be about 16" depending on the brand. watch for birds , they like to fill the air spaces with nesting material, no air flow bad fire! triple wall is a problem there, whereas double wall has no openings, just costs more. good luck, Stryder Quote Link to comment Share on other sites More sharing options...
Rick Barter Posted June 27, 2006 Share Posted June 27, 2006 Thanks, Stryder. One question, though. I'm struggling with figuring out how big the opening will be and how it needs to be done. I was figuring on asking the stove shop and having installation instructions with the pipe. However, more opinions are always preferred to less. rvb Quote Link to comment Share on other sites More sharing options...
Rick Barter Posted June 27, 2006 Share Posted June 27, 2006 Ahhhh! I actually found what I was reading: Cut Roof Opening: Cut an opening in the roof directly above the opening below, and at least 4 inches larger than the chimney Quote Link to comment Share on other sites More sharing options...
henerythe8th Posted June 27, 2006 Share Posted June 27, 2006 Rick, You probably already realize that the hole will be eliptical but is not really that critical. I've known folks that got all up tight about making the hole precise... If you're "one of them" a couple of methods come to mind. One of the simplest is to get a helper to hold the pipe plumb, centered over the hole to be and trace with a "long pencil" around the perimeter. The slope of your roof may mean that you need a pencil that is longer than normal... you can stick a pencil into a piece of tubing and to extend it. H Quote Link to comment Share on other sites More sharing options...
stryder Posted June 27, 2006 Share Posted June 27, 2006 I always set the support box then went up with the chimney till i got close to the roof, remember lateral bracing as needed to keep system rigid. this can be simple straping tape or 2" wide sheet metal of light guage. i then use a level against the pipe and a pencil to mark the outline on the roof, run a screw up in several spots on the pencil line up thru the roof. then i go up top find the screws sticking up, and (depending on what type of flashing used the flexible is best for metal roof) center flashing and mark inside outline onto roof. cut out that hole and your'e there. finish chimney and seal flashing. hope i haven't rambled on. Stryder Quote Link to comment Share on other sites More sharing options...
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