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forge chimney

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I'm just learning this blacksmithing thing ,and so far I just love it . I get out in the shop and loose alllll sence of time. I'm putting up a new shop. It's a double carport and I put wood ends in it.My question is I don't know if I should put the chimney out the side of the wall,then up ,or up through the roof . Up through the roof I will have leaking problems,if I go through the wall I might have draft problems. I will be using 14inch signal wall pipe for the chimney.

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As this is not built yet, why not test out the system before you make it permanent.

Small one man hobby forges do not require industrial strength hoods. The 14 inch diameter pipe concerns me as being overly large, as I would like to see the results of 14 inch vs 12 inch vs 10 inch under your conditions.

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I'm fixin' to put a chimney up in my shop. 10" pipe will be sufficient for it and allow enough draft. Just remember that if you are going to go through the side, stay away from 90 degree angles. A straight shot is best. But if you have to, go with 45 degree angles.

Using a chimney pipe pass through on the rood as well as flashing and tarring should take care of any leaking.

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I made a side draft just as Uri has. Since my last shop burned down, I am concerned on safety. The horizontal part goes right through the side wall, contacting the drywall, a tight 2x4 frame, and then rough sawn siding.

In my first test, the side draft gets warm to the point you can touch it, but not hold your hand on it for more than a few seconds.

I am thinking of cutting the side draft off flush to the wall and then putting a smaller side draft inside. This would be an inch smaller on all sides, the extra space would be filled with insulating putty. This would give an insulated double walled pipe through the thickness of the wall. Since the outer pipe is cut off at the inner wall, the only heat would be radiating the distance to the forge, no conducting.

I suspect this will keep the outer tube cool.

This is way overkill, but I like it better.



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Glenn, Reb,

After picking up supplies, I am not using the insulation. I will go with air gap.

I do not have a way to draw anything right now, but here is the plan:

The wall is composed of:

Rough saw siding-- 2x4 -- Drywall.

13" square hole through the wall is the same size as the outer metal tube. The 2x4's are touching the outer metal tube on all sides. Not terribly tightly because the metal shell bows in on the four edges. The 13 inch hole through the wall could be enlarged if needed with some amount of effort (it was framed in before the drywall was put in....) I have 16 inch on center studs.

I have now got thin steel plates, 1'x2' and angle iron from a bedframe. I will make an inner square tube (see photos for raw supplies).

Now, Glenn mentioned leaving the space open. I was going to seal it off for better draw, but I doubt it is needed. I will just have some metal bars inside the air gap to space the inner tube from the walls.

There is some warping in the original, so the air gap will vary, and might actually touch a little. Over all the effect will be there.

More thoughts?


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Think of any way there will be a transfer of heat and try to eliminate it.

You can drop the temperature and radiant heat from a heat source with a metal shield and an air gap. It drops even more with a second metal shield and a second air gap. There has to be a certain amount of air (space) gap for best efficiency.

Fortunately in your case, there is a lot of fresh (read cooler) air being sucked into the chimney along with the smoke. This air MUST be replaced by leaving a window or door open to let new air into the building / room. All this new air has a cooling effect on the air being sent through the horizontal tube. Be sure to check the temperatures of all parts of the chimney, AND the building, walls, etc, to be sure that even under full load, they do not over heat.

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It was a simple statement, but it makes me think:

"Think of any way there will be a transfer of heat and try to eliminate it."

I have tried from two computers, I am not able to add the photos as an attachment, they are under the size limit. Anyways, here is the plan:


Cut off the horizontal side draft chimney to 1 inch proud from the inner wall.

Use drywall screws to pull the outer shell back to flat to the 13 inch framed hole. Not that there is a real hole through the side draft from this, but I have chimney cement to cover these holes.

Lay down a 1/2 inch kaowool blanket two inch wider than the wall thickness all the way around the inside of the 13 inch metal outer shell.

Put 2 half inch metal spacers on top of the kaowool at each edge of the inner shell. (so four on the floor, four on the ceiling) This will keep the inner shell centered.

Screw 4 L beams through the spacers, kaowool, and outer shell into the 2x4 framing. These reach to the edge of the fire pot on the bottom, and half way over the fire pot on the top.

Lay down the thin steel sheeting into the four L beams, completing the box. Bolt the thin sheet into the L beams. Possibly seal with chimney cement.

Use extra kaowool to frame the wall surrounding the outer shell. Should be about 7 wide around.

Cover the kaowool frame with a wider metal plate, to the width of the forge.


This would be better with pics, but they are not attaching! :(

If I was super paranoid, I would be concerned about the screws from the inner shell transferring heat into the 2x4 frame...

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