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I Forge Iron

Forge hood problems


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I build a super sucker side draft for my forge some time ago and it use to work really well untill I got it in my new shop. If my fire is in the back of the fire pot it works well but if it starts up in the front the shop fills with smoke till the coal cokes up. Though about adding a larger hood over the super sucker but could use a few ideas if anyone has a couple.
I'll try and attach a picture of my forge.

post-7651-001152900 1276055465_thumb.jpg

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The standard suggestions apply, straight stack with no bends or angles, chimney top should be 3 feet or more above any obstruction within 10 feet of the chimney, and watch for buildings, trees, or other things that could cause air flow or downdraft problems. The size of the chimney matters, both in diameter (10 to 12 inches diameter being recommended) and height (3 feet above the nearest obstruction) does matter. If in doubt, add 3-4 or more feet to the chimney height. There is also the problem of creosote or material build up inside the chimney. Chimneys do need cleaned on a regular basis.

There are two (for this discussion) types of rooms, those so loose you can throw a cat through the wall without harming the cat, and those rooms that are air tight. To see how much air a chimney requires, go outside (leaving the door open) and look at the volume of smoke coming from the chimney. That is the same amount of fresh air that MUST be allowed to enter the building. This makeup air can come from windows, doors, or leaks in the walls etc, but it must come from somewhere or the chimney will be starved, produce less draft, and many times let smoke escape into the room.

Open a window or door and let air into the room to replace the air that is going up the chimney. IF the forge sets near a wall, you can pipe in outside air to the blower to be forced into the fire, or pipe outside air to a location close to the forge so it can blend with the smoke and go up the chimney.

I have used the same forge hood, and forge set up and changed nothing but the diameter of the chimney. All this was done outside so makeup air was not an issue. Chimney height in all cases was about 6 feet, hood height was about 3 feet, and the hood has a 10 inch diameter outlet. For testing, I used 8, 10, 12, 14, 16, and 18 inch chimneys on the very same hood with approximately the same chimney height. 8 inch worked but poorly, 10, 12, and 14 inch worked increasingly better, 16 inch was showing signs of problems and 18 inch had poor draft in this set up. I suspect that increasing the chimney height would have improved the draft in all cases. I have also used a 24 inch diameter chimney at the same chimney height, but with a different hood and forge configuration and it works very well.

One thing that must be considered is the weather conditions. Heavy weather will make a chimney draw differently than a clear day. I have experienced a fire on start up push the smoke out the top of the chimney and that very smoke then fall to the ground and flow across the ground like water or fog. I have also seen the smoke just clear the top of the chimney and then fall back onto the forge table to be sucked back into the chimney. This is indeed unusual and fixes itself with either a slight air movement (wind) or with a larger fire and increased draft, or both. The smoke then moves away flowing like a fog very close to the ground. Weird yes, and completely attributable to the weather conditions.

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I need to explain more in that my shop is a 12 x 10 all metal building no windows and 1 double sliding door. I did put in a 12" x 12" louver type window with a box fan in front of it blowing out. It is on the wall across from the doors to help draw air through the shop, I hope. My chimney is about 3 feet above the roof line but there is another building 6 feet away taller then the chimney on only one side. The pipe is an 8" pipe about as big as I could find around here. I'll try adding more pipe to the chimney and see how that does. I will have to say too that when I first used the super sucker I was working outside, the shop I have now is the only shop I have used this hood in.
I might even try the plains off the web sight you sent Eric to build a new hood or add to the one I have anyway I'll try something till it works. Thanks folk for your input and help.
Bill P

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Hi Bill, I've had similar problems with smoking at startup with my side draft flue.
I used a piece of roofing metal to make an easily removable extension for the entrance to my flue.
If I've linked this correctly, you should be able to see some pics here:
Hope this helps!

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