I Need a New Plan

[tjdaggett]

I'm stuck. So far, I haven't been able to figure out how to legally put a chimney into the shed. Here are the options I've thought of with their respective problems. 

1. Put a black, single-walled stove pipe straight up through the roof. These require a minimum clearance of 18 inches between it and combustible materials in order to be up to code. That means a four-foot circle (counting 12" pipe) cut out of my roof. No can do.

2. Do the same, but with double-walled chimney pipe. There are some of these that do not require clearance to combustibles, but their exteriors are mostly galvanized. I don't want galvy hanging over my forge. Also, the bill would be a solid $600 or more, which is right out.

3. Run the chimney out the wall to get the distance from combustibles, then up. This would mean replacing a chunk of my wall (currently plywood) with non-combustible material around the chimney. 

4. Look into building a masonry chimney. This seems like a whole other can of worms and would probably require pouring a slab. 

5. Make something out of earth. I don't currently have a source for clay, so this seems even more expensive.

Some more basic info, which you guys probably already know from my other post:
- 8x10 wooden shed
- Working in a residential backyard
- Good relationships with neighbors and city; want to keep it that way
- I have zero welding capabilities, though I could ask if anyone in the local guild could help

Thank you for your expertise. Several times you guys have provided the spark I needed for the next step. I really appreciate it. 

[Chris Williams]

38 minutes ago, tjdaggett said:

3. Run the chimney out the wall to get the distance from combustibles, then up. This would mean replacing a chunk of my wall (currently plywood) with non-combustible material around the chimney. 

A sheet or two of hardiboard or equivalent cement board wouldn't cost that much (~$35 for a 4'x8' sheet). You can replace just where you want the chimney to be, or a full wall. Make sure to use a wet process to cut it, as the dust is a real hazard. 

I haven't bought them before, but I just priced steel studs, and they aren't much more than wood. Check out the hardiboard installation guides before committing to this combo though. 

[ThomasPowers]

Galvanized is NOT an issue that far from the forge.  Just a couple of feet from the opening of my chimney I can use the 10" pipe to warm my hands with no burning!

 

[Steve Sells]

you only have to have double wall at the roof line, not for the entire thing.

[ThomasPowers]

The woodstove in our house has a stainless pipe for the first section, then black pipe for several sections and then goes into a galvanized double walled pipe for the roof penetration and up to the cap.  (Lovely peacock temper colours on that first section!)

[Welshj]

I'm not sure of the terminology I'm going for... but what about a box style side draft hood(?) Over the forge inside, going to a pipe out of the wall higher up.

I've seen a few versions in pictures, cant recall where. But it would reduce the needed amount of double walled pipe, be less of a concern with heating combustibles and not have to go through the roof.

[Yanni Rockitz]

So what did you end up doing on this forge hood / flu thing? I'm installing one right now and keep going back and forth about whether to go out through the wall then up, or straight up. It's going to be a side-draft super-sucker, either way. I know straight up is the best draft, so I got a "High temp" Dektite #7 red silicone metal roof flashing / boot to put my 12" single-wall pipe straight up through the curvy/wobbly corrugated galvy metal roof panel, but then I realized my roof rafters are too close (24" total, so only like 6" either side) for code and I saw some guy's pics of one of those silicone boots in flames and realized I can't be sure it will definitely withstand the heat of a single-wall flu pipe coming up off the forge at full welding heats. I REALLY don't want to risk any kind of fire out there near the woods where I built the smithy. The Dektite red silicone is rated for 392F 'continuous' temp contact and I'm not sure the single-wall black flu pipe won't go higher than that ~7' above the fire. So yeah, I know -- "Use double wall insulated for the roof penetration", but that stuff is EX$PENSIVE! Like hundreds of dollars, at least. I've answered my own question:  Much easier to just cut a big hole in the plywood side of the building, frame in sheet metal or hardiboard / cement board (some less costly non-combustible) then go out the side and up, keeping the standing stack 18" away from the side of the building, with some metal bracing to support it against the weather. That way, you don't xxxx with the roof and there's no sillycone risk. I've seen some designs for those that look good -- just have to fab up a 12.5" square 'duct' for the bottom to go out the wall. Angled face with a 10"x10" opening to create the 'suction' into the larger 12" pipe. Weld a collar on the outside hole for the round stove pipe to seat into, make sure it has a slight down-angle for rain to drain off to the outside -- good bracing to the side of the building, a custom rain cap a good 12" or higher above the top, a ~1/4" galvy critter screen / spark arrestor around the top -- "Bob's your uncle." (Maybe?) Anyone else done this? One example I saw in here had four of them coming out the back of his shop and said the draw was plenty strong.

[Frazer]

Have you talked with the code office/fire marshal in your town? The laws around chimneys and vary widely depending on what sections of NFPA 211 your town has adopted.

What you describe sounds similar to Hofi's side draft:

 If you want things done to code it's going to be relatively expensive no mater what. That has been my experience anyway.

[Frosty]

NO silicone calk!  392f rated silicone calk is for what? You'd be a fool to use automotive high temp RTV silicone adhesive and it's rated to 750f. last time I looked at a tube. That product will not only burn, the fumes it gives off before lighting up are pretty toxic. If you even considered using calk you really NEED to have a professional do this for you. You may have to save up to have a pro install the stack but what will it cost to replace your: kit, the shop and whatever else catches fire when you burn yourself out saving a couple hundred bucks?

A triple wall roof jack isn't that expensive. Proper flashing and a rain collar will probably tag on another $100 or so. But I've installed and helped with smoke stacks a couple few times. Doing it right costs some. Not doing it right can not only cost you everything you have or are likely to earn replacing other peoples property but can even end up doing jail time if say someone dies in a house fire started by your shop burning down. 

This isn't a trivial thing, this is REAL WORLD SERIOUS.

Frosty The Lucky.

[Frazer]

I too would recommend, if not having a professional do the installation itself, to seriously consult a professional to make sure whatever you plan to do is safe. I ended up hiring someone because I quickly realized this was way outside of my area of expertise. There is a lot more to a chimney installation than directing smoke. Permits, local laws, homeowners insurance, etc.. It helps to have a someone familiar with the whole process working with you to save you from making a big mistake. 

Parts are indeed expensive (that's why I ended up going with a 10" system rather than 12"), but a chimney is not a good thing to skimp out on. Like Herr Frosty said, if something goes wrong because of something YOU did, the consequences can be quite serious. The powers that be won't take "I didn't know" or "I read online that it was fine" as an answer. You will foot the bill to replace the structure and all of your stuff out of pocket because you did the work, you cut a corner and you didn't tell anyone what you wanted to do. That's the way it goes and there are many examples of this exact thing happening. 

I'm not trying to give you a hard time, but I think the more you look into it you'll realize that trying to save a couple hundred bucks on pipe and parts isn't worth it.

Do it once, do it right and you'll sleep better at night.

[BillyBones]

You can save a few bucks if you can find a sheet metal fabricator that can make the pipe. Not a lot mind you 10 or maybe 15%. Many sheet metal places wont do it though becuase of liability.

The insurance and liabilities are one issue bet let me ask, how much is your life or the life of one of your loved ones worth? Will those savings make you or your family feel better if the shop burns with you or one of your kids trapped inside, or even both?  Worst case scenario yes, but still a possibility. 

Also a note about that silicone, i worked for many years on cars and i have seen that silicone burn off of exhaust systems. What is used on exhaust systems is more of a clay, we just called it muffler putty. Ideally you use a metal gasket on exhaust. 

I do not know about code where you are at, but here i can run single wall pipe up to within 18" of the roof. Then a class A pipe out the roof for 18" and the top can be single walled. And even a class A pipe has to have at lest 6" between it and any flammable material. So i can get a 4' piece of class A and the rest cheap single wall. However, heat, rain and sulfur do not mix well and end up eating holes in cheap old single wall pipe. Basically makes acid rain inside your flue, or at least that is my understanding. 

Like frazer said though, we are not trying to give you grief. We want you and your family to be safe. Do not skimp on safety. 

[Frosty]

A few years ago we had to replace the stack on our wood stove. We used stainless triple wall from the slip joint to the rain cap. 22' of 6" triple wall plus installation ran us $1,700 and change. The contact thermometer I have on the stove hits an easy 450f when a fire is rolling, my laser thermometer says the double wall slip joint pushes just under 200f. The triple wall directly above can be held in your hand untill you're tired of the position. I don't recall the brand name but it has a stand off from flammable surfaces of 1" and has an unlimited lifetime guarantee against any failure. If it fails and burns the house down, they'll replace the house and lost possessions. Between the inner and second SS layer of pipe is 3/4" refractory blanket. They call it rock wool but a little digging showed it to be a 2,000f ceramic blanket refractory.

The Jotul parlor stove was a discontinued, 3 burn zone side loader and carries a lifetime guarantee. One of the rope gaskets on a door got snagged and was starting to leak, the stove company sent a couple guys right out, replaced the rope gaskets in all 3 doors, cleaned and inspected the stove and stack and put a fresh coat of paint on the stove. They even cleaned the window. All part of the guarantee, they billed Jotul. Being a 3 zone stove it doesn't smoke once it warms up a little. Seriously the only time anything but heat distortion comes out the stack is the first 3-4 minutes after you light it. Even then, if you put a brown paper shopping bag in the stove when you light the kindling you get maybe 30 seconds of smoke. 

Yeah, we spent a bit more than $4,000 for the stove on sale and another $1,700+ for the stack but it's been worth every penny. I can leave a fire rolling in the stove, go to bed and not miss a wink. 

You haven't enjoyed an adrenaline rush until you get a call from your wife asking what to do. The stove pipe is ORANGE and ROARING like a rocket! "HANG UP CALL 911!!!" "Get as many pest as you can grab and GET OUT OF THE HOUSE. Do NOT TRY TO SAVE ANYTHING BUT WHAT YOU'RE WEARING! 

Is she going to do that? HAH, she ain't abandoning HER HOUSE without a FIGHT! "What do I do?!?!" Resigned to the inevitable I say, "grab the fire extinguisher be the front door, bang it on it' side on the floor two times. Pull the safety pin, it's large and yellow. Crack the stove door, aim the nozzle up and towards the right back of the stove. Now the hard part Darlin you MUST give it brief puffs, if you hold the trigger down it's going to blow so hard embers WILL come out the door. Just puffs until the extinguisher is empty. Then GET THE blank OUT!"

When I'd answered her call the other guy in the truck with me told me to switch places and he started driving for the shop where our cars are parked. After I hung up with Deb it occurred to me she hadn't called 911 so I did. The dispatcher reassured me a heavy engine company was on scene. I didn't call 911, I called dispatch on the radio. Of course that meant everybody working that shift knew and had my personal gear from my locker waiting at my car. The shift foreman yelled "Don't talk GO!," as I jumped out of the moving truck. Happily Jay drove to my car and had almost stopped. It's an hour drive but two state trucks were already on the road, one from the Palmer camp. 

Turned out Deb called 911 before calling me. Smart woman! I got home to find all well except the wrinkly stove pipe one really EXCITED wife and 5-6 state highways guys looking to help. She said the fire chief told here she'd done exactly the right thing, the fire was out when they got there and he showed her a better way to fight a run away stove or stack fire. He took the decorative cup off the "mantle" dipped some water from the pot on the stove and tossed it in the stove door. It hissed, whooshed steam up the stack. Do that until it stops whooshing and keep an eye on it. The water cools the coals and the steam smothers the fire instantly while cooling the stack. 

I've never had anything but the best stove and stack I can afford in the house. We also keep a pot of water and dipper on the stove. 

Frosty The Lucky.

[Yanni Rockitz]

Wow - I come back a week later and the whole gang has chimed in.  ;-)  Good info all around! I didn't mean to hijack this thread -- just looking to do the same thing and there's obviously tons of experience here. I'm wondering if my explanation was maybe causing some false alarms... The "roof jack" (flashing boot that holds the stack to the metal roof panel) I originally got is a Dektite #7 "Hi-Temp" unit. They state that the 'boot' part that you cut to size to fit the pipe is made of 'high temp' orange (rubber? ...silicone?), but it's clearly not rated for what I would consider anything close to truly high temps -- only for continuous contact with 392F, which is not high enough at all for single-wall -- maybe not even for double-wall, though I suspect that may be okay. I doubt an open-air super sucker off a coal forge firepot would cause the flu to exceed 392 six feet up. I know I can hold my bare hand against the 6" double wall stainless on my house wood stove flu when it's running hot and that pipe's outside is only warm -- doesn't burn the hand. The only reason I got that roof jack with the orange rubbery boot was because it had the bendable aluminum strip that would form to the wobbly ('corrugated?') galvy roof panels on my building and I'd seen some others had used them and liked them. I (thought?) I was having trouble finding 12" stainless double-wall/insulated pipe sections to go up and out, but have since found them online. It's still easily $300 for the top two sections I'd need to go up and out the roof, so it will be a lot cheaper and easier to just replace a section of plywood wall with hardiboard or some other 'cement' non-combustible and go out the side, then up with single-wall. Maybe sandwich in some rockwool or other fireproof insulation like leftover kaowool between the two layers of cement board wall inside the frame with an air gap around the metal and go out the side above the forge. I am indeed thinking of a Hofi-style side draft with a 13"x13" duct (fabricated out of 3/16" sheet about 4' to a box end that has a collar to seat the 12" round single-wall stove pipe going straight up from there. I'd plan to space it at least 19" off the side of the building so it's well clear of the 18" to combustibles code. I know the sulfurs and weather will eat up that pipe in a few years, but to get up and running on a budget, this is many hundred$ cheaper than doing double-wall. the black pipe sticking up off the back with woods behind it should also be less conspicuous than having that orange thing on the roof with stainless. Knock on wood! I noticed the Hofi side draft is 13" square opening at the fire. Would a 1" lip around it (to reduce it to 11"x11") create more of a super sucker effect? I'm personally REALLY paranoid about fire safety, and the new smithy is out by the woods, so I'll probably only run the coal forge when it's wet and/or snowy -- which is a fair amount of the year here in Maine. Gas forge the rest of the time. We'll see how that goes.  ;-)

[Charles R. Stevens]

Framing a 4”opening either in the wall (like a window) or threw the roof isn’t all that bad, it can readily be covered with a sheet of tin. Insulation is always a good idea, and can be accomplished with kool wool or the like close to the pipe. Look at the the roof jacks for zero clearance fore places, as that is essentially what your building. If 12” isn’t a standard size, try 10” as it may be less expensive. 
Uri Hoffi uses square section threw the side wall with round pipe as a stack successfully at his school. 
often we forget that we are essentially installing a fire place, not a wood stove or industrial furnace. The volume of room air that goes up the chimney cools the exhaust air significantly. 
a 4’ length of class A double wall With a stainless inner  pipe runs less than $200. You only need single wall from the forge to ceiling and roof to cap. Any way you cut it if you  buy a thimble and roof jack for 10-12” pipe it’s going to be pricey. 
depending on your scrounging skills, and what you can live with, a few sheets of corrugated or roofing tin either for the wall or from ridge line to below the chimney is probably the least expensive option.