Chimney/hood design

[isaacsbees]

Hi everyone, this is my first post on the forums...

I apologize in advance if this post isn't where it belongs or in the correct format.

I've been lurking around on here for the past few days without an account just taking in all of the information about various systems of sucking smoke away from coal forges.

After forging outdoors for awhile without a hood (still very new to forging), I've decided to move indoors. I noticed y'all like details, so I tried to get as many as possible:

-Forge has a 12" x 10" firepot set into an old 18.5" x 16.5" forge body (measuring from the top of the sloped edges)

-Cinderblock behind the forge is 15.5" x 7" and the top of the block is roughly flush with the upper back lip of the forge

-The forge/cinderblock is 10" lower than the windowsill

-The window is approximately 27" square and I have cut out a piece of 3/4" plywood to fit into it (still not quite sure how I'm going to safely pass the pipe through the plywood without it being a fire hazard)

-The building has a gently slanted roof, and this window is on the side with the high end of the slant

-From the top of the window to the highest point of the roof is 30" (bottom of the window to the roof is 57", forge to the roof is 67")

-I have access to some 8" round, galvanized vent pipe left over from another project: one 2ft piece, one 5ft piece, two adjustable 0-90 degree elbows, and a rain cap (I know I will need more than this, but it's what I have on hand at the moment)

-For cutting/drilling/connecting metal, I have a stick welder, tin snips, hacksaw, jigsaw, miter saw, angle grinder, power drill, and various blades/bits. I don't have a plasma cutter.

 

Can I get away with using 8-inch round ductwork for a smaller forge like this with the proper hood (I know that 10-12 inches is preferred)? If so, how much more pipe do I need to buy to make the stack tall enough? Or am I better off buying larger round or square duct? 

 

What is the best shape for the ductwork to preserve flow in this case? Should I do an "S" shape (up, out of the window horizontally, then up again) or will that slow the flow too much?

 

Is a Super Sucker the best route to go down? I've also seen people use 55 gallon drums and was thinking about that as well.

 

In general, I'm sort of lost on this project and the fluid physics/geometry involved and need some guidance from more experienced hands. Thanks for reading!

 

-Isaac

 

 

 

[Goods]

8” vent is not going to draw very well if at all. 10” would be a minimum. Mine is 10” and I wish I went with 12”.

If you’re going to go through the window, try to through at a 45degree angle. Two 45’s and no horizontal section will help with the draw also. 

I also would avoid putting plywood in the window. Cement board would be a much better choice.

Just my two cents, there will probably be others posting with additional good information.

Keep it fun,

David

[Steve Sells]

buy the 12 inch, its not that far to the window. Dont cause yourself problems, you need to breath

[isaacsbees]

1 hour ago, Goods said:

8” vent is not going to draw very well if at all. 10” would be a minimum. Mine is 10” and I wish I went with 12”.

If you’re going to go through the window, try to through at a 45degree angle. Two 45’s and no horizontal section will help with the draw also. 

I also would avoid putting plywood in the window. Cement board would be a much better choice.

Just my two cents, there will probably be others posting with additional good information.

Keep it fun,

David

Thanks David! I never thought to use cement board... good idea! 

1 hour ago, Steve Sells said:

buy the 12 inch, its not that far to the window. Dont cause yourself problems, you need to breath

I'm leaning toward just ordering the 12"... how tall do y'all reckon it'd need to be to give a good draft? Could I connect 4" with my 8" to make some of the 12" I'll need?

 

Thanks for the quick responses guys!

[Frosty]

The stack will need to be at least 3' higher than the highest part of the roof that's close. Check the local code or give the local FD a call. The FD would much rather answer these questions than visit you professionally. 

You can buy "wall jacks" to safely pass stove pipe through walls but a sheet of concrete backer board is WAY cheaper. 

Super suckers work really well but I doubt you want to cut a hole through the wall just to use one. Hmmm?

You can still make a side draft hood which work better than an overhead hood and you have more than enough tools to make one. A square "Blazo" can works a treat as a side draft hood and all you need are a drill motor and bits, tin snips and sheet metal screws.

More later I tend to get carried away.

Frosty The Lucky.

[Irondragon Forge ClayWorks]

Welcome from the Ozark mountains. If the building is yours and you are not opposed to cutting a hole in the concrete block wall and moving your forge to the side of the window. I recommend the Hofi side draft chimney. That would be a win-win you get to keep the window and have the best chimney system I have ever seen and used. The box on your building would not have to be as long as in Uri Hofis school, just long enough to clear the roof overhang.

I can't control the wind, all I can do is adjust my sails.

 

 

 

[isaacsbees]

14 hours ago, Irondragon ForgeClay Works said:

Welcome from the Ozark mountains. If the building is yours and you are not opposed to cutting a hole in the concrete block wall and moving your forge to the side of the window. I recommend the Hofi side draft chimney.

 

I'm not opposed to cutting a hole through the wall... I've just never cut through a concrete wall What would be the best way to do that?

16 hours ago, Frosty said:

The stack will need to be at least 3' higher than the highest part of the roof that's close. Check the local code or give the local FD a call. The FD would much rather answer these questions than visit you professionally. 

You can buy "wall jacks" to safely pass stove pipe through walls but a sheet of concrete backer board is WAY cheaper. 

Super suckers work really well but I doubt you want to cut a hole through the wall just to use one. Hmmm?

You can still make a side draft hood which work better than an overhead hood and you have more than enough tools to make one. A square "Blazo" can works a treat as a side draft hood and all you need are a drill motor and bits, tin snips and sheet metal screws.

More later I tend to get carried away.

Frosty The Lucky.

Ok, 3 feet minimum over the roof and concrete backer board, got it. For the Blazo can, is it something like this?

[Irondragon Forge ClayWorks]

Cutting concrete blocks with a hammer and chisel is easy. The blocks are hollow with a web in the center, best to work from both sides alternating the chisel scoring along the lines you have drawn for the outline of the hole you need. They are held together with mortar which is relatively weak. Most building blocks are 16x8x8 inches. A Skill saw with a masonry blade will make short work of them. Be sure to wear PPE (eye protection, dust mask, etc.). If you google concrete block it will bring up all the images of the different blocks.

I can't control the wind, all I can do is adjust my sails.

[isaacsbees]

Ok y'all, I think I'm going with 12" pipe through the window, just so I don't have to punch through the wall. I'm gonna take Frosty's idea to get something like a blazo can and fit it up with the forge, making sure the area is less than the area of the 12" pipe. I just went down to our local HVAC supplier got some 12" stuff. Thanks again to everyone for your help on this!

 

-Isaac

[Frosty]

Ayup, those are Blazo cans, it's the only product I can think of that comes in square cans like that. Be aware if you do use a Blazo can it had white gasoline in it so be very careful. 

Frosty The Lucky.