Stovepipe chimneys

[BB4]

Hi everyone - my name is Bill, and as you all may have guessed, I'm new here.  I'm setting up my forge, and have run into a crossroads of sorts on how to proceed.  I'm trying to decide which size and set up I should go with to vent my hood.  I'm on the fence on whether I should go straight up through the attic space, and out the tin roof, or make a 90 degree out the wall, and then up to appropriate height.  I'm also not certain on pipe diameter...  Six inch, 8 inch?  I've been pouring through information both here, and around the internet, and I'm seeing conflicting opinions.  Attached are some pictures of my set up.  I welcome any and all information.  Thanks for reading, and glad to be here!  

[Goods]

6” or 8” diameters are both too small. I went with 10”, knowing the recommendation of 12” diameter… 12” would have been much better!

Roof penetrations can be problematic, so I can understand wanting to go through the wall. If you’re going to go up then over, consider going through the wall at a 45 degree angle. This would create less of a flow impediment. Of course, I would recommend a side draft hood and I believe Uri Hoffi’s side draft hood went  straight out through the wall then to a tall stack. (I’ve personally never seen one setup that way though.) The are some really good designs out there, just make sure to follow the dimensions… There’s a read they work well.

Keep it fun,

David 

[George N. M.]

Bill, welcome aboard from 7500' in SE Wyoming.  Glad to have you.

Before I mention chimneys I think you may want to rethink your forge a bit.  First, and IMO, the most important, your fire pot (the brake drum/rotor) is too inaccessible.  You are going to have problems getting work into the hottest part of the fire because of its depth and the way the hood is around it.  Ask yourself how you are going to heat the center of a 3' piece of stock.  At a minimum you need to cut a pass through in the back of the hood so that you can get the long piece of work lying across the fire pot.

Also, move it away from the walls a bit.  I'd say 18-24".  And I'd think about putting concrete backer board on the walls behind the forge.

And the flat top on the hood is not optimum for the smoke to draw up the chimney.  You might think about getting another drum and making the hood higher and cutting gores (long, skinny vertical triangles) in it to make the top, leading into the chimney, more cone shaped.  It's more work but probably worth it to get the best draw you can. 

Goods idea of a side draw hood is good if you want to go that direction.

As for chimneys, I'd say that a 10" diameter would work well for a forge of this size.  I'd take it straight up through your attic and roof.  Yes, you can put in 90 degrees angles but it is never going to draw as well as a straight run chimney.  Also, keep the chimney as far away from joists or any other wooden parts as possible.  Use a pretty large jack while going through the roof.  And extend the chimney above the highest point of your roof (2' is often recommended) to prevent turbulence from the wind reversing the draw of the chimney.  And put a rain cap on top.

"By hammer and hand all arts do stand."

[George N. M.]

PS Think long and hard about a double wall pipe while going through the roof.

Also, your state, township, or municipality may have fire code requirements you will need to follow.  For example, there may be a need for an 18" setback from any flammable material such as walls or joists.  Sometimes these cannot be met, e.g. when the ceiling joists are 24" apart.  Check with the building and/or fire inspector to see if the codes apply to you and if there are work arounds.  Wood stoves are common enough in your area that there should be common practices for them (although a forge doesn't put out anywhere near the amount a medium sized wood stove does).

G

[Irondragon Forge ClayWorks]

Welcome from the Ozark Mountains.

Like George said, you really need to adapt the forge and fire pot so you have more working space around it. The brake rotor will work for the fire pot but should set down against the drum top which will be the table where your fuel will be so new fuel can be raked into the fire as needed. With the rotor dropped into the bigger hole, you will still have about an inch of the rotor exposed and that can be filled in with clay sand mix to make the table even with the fire. The clay will also insulate the drum top keeping it from burning or rusting out.

To go with a side draft chimney system you really should scrap the hood and build a "super sucker" side draft. Going straight up through the roof would also be my choice. Here is just a couple of pictures of my setup which has been working fine for about 30 years now. Also you didn't tell us what your air supply & fuel will be coal, lump charcoal or something else.

As you can see I had to modify my hood for a better draw and the stack goes straight up through the roof. The forge under the cover is our propane forge.

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus

 

[BillyBones]

Welcome.

As said before look up what your local codes say about it. They can be kind of tricky if you use the interweb, however your local building inspectors office should be able to give you a print out of what it is. Even if you do not live in a town you still have to find what the county or state codes say. Here i have to have 18" from stack to any flammable object for single wall pipe, triple wall (the kind with ceramic blanket between 2 pipes) is 3" from flammables. THAT IS FOR WHERE I LIVE. (caps for emphasis) 

My stack has 2, 45* bends rather than a 90*. ( i go through the roof but rearranged my shop not long ago and did not want to cut another hole) The draw will be greatly reduced with a 90* compared to 2, 45*s. Imagine how much more you have to slow down driving to take a 90* turn compared to a 45*. I use 8" pipe, becuase 10" triple wall is almost impossible to find here and costs an arm and a leg when you do, it works ok. If i have the windows open and a breeze in the shop it gets a little smoky for a few minutes but not unbearable. However my exhaust fan works great and pulls it out in a couple minutes. Regardless of stack size i would recommend and exhaust fan if for no other reason than to keep air circulating. 

I also second, or third(?), the opinion of making the top of the hood a cone. Think of it as an upside down funnel. 

A bit off subject, but i would either move that fire extinguisher or place a second one next to the exit. General rule of thumb is that they are placed near an exit so that if there is a fire you do not go towards the interior of the building for it but towards an exit.  That is so that you can avoid a worst case scenario of being trapped with the fire between you and the exit. 

Anywho, stay safe and have fun. 

[George N. M.]

Another safety item that you should have besides the fire extinguisher is a carbon monoxide detector.  It is probably less necessary if you are using a solid fuel forge than a propane but is still a good idea.  The most hazardous time for CO is in the winter when you are trying to keep the shop warm and the cold air outside.  That is when you start getting incomplete combustion and the production of CO.  Always make sure you have enough open spaces for air to get into the shop, even if it is cold air.

A friend of mine was running his propane forge in a garage with all the doors and windows closed and his wife found him on the floor between the forge and the door.  Luckily, he was just unconscious but he had to spend a good amount of time in a hyperbaric chamber (high pressure oxygen).  He said that it was not a fun experience.

"By hammer and hand all arts do stand."

[Goods]

Side note, when I setup my forge I put a vent in for fresh air to my blower. My theory was to create positive pressure in the shop to help with draw on the hood. I have pretty good draw with one window only open 3” inches in the winter. Honestly, no different than summer when I have the overhead door open to keep the heat down. I feel a 12” stack is what would make the biggest difference (or maybe 10’ taller, but that would take more stack support for wind loads…)

Keep it fun,

David

[BillyBones]

I can try an seal off my shop but that is near impossible, especially with the 4" x 18" gap at the bottom of the door so the cats can come in and out. 

One other thing i forgot to touch on, do not skimp on the pipes. Get good pipes and not the cheapest you can get. If you are burning coal the Sulphur in the coal when burned will combine with any condensation or moisture. That will create sulfuric acid and you will be replacing those pipes, especially bends, in the next 18 months if not sooner.  

[Frosty]

About sulphur combining with condensation or other moisture. Moisture is a combustion byproduct, so H2SO4 is inescapable in your stack. 

Frosty The Lucky.

[BillyBones]

You are absolutely correct Frosty. 

Just in case i was not clear, i was not saying that the pipe would stop the sulfuric acid but that cheap pipes will rust away much faster than good quality pipes. 

[Frosty]

I wasn't contradicting anything you'd said, just adding a detail some of the gang reading might not know or think about. Better quality usually lasts longer and performs better. I wonder if anybody is making stove pipe powder coated on the outside AND inside?

Even stainless pipe won't last forever just longer. I just don't know if it's worth 4-5x the $ longer.

Happily coal is too much hassle to collect so I run propane on those days I light a fire so I don't have quite the corrosion issues.

Frosty The Lucky.

 

 

[Steve Sells]

I cheated to avoid that problem, mine is brick

[BillyBones]

Frosty, i did not think that you were. I just wanted to clarify incase anyone else thought that was what i was inferring. 

[BB4]

Thank you all very much for your input- you've certainly given me a lot to think on.  I greatly appreciate it.