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I Forge Iron

Why doesn't my super sucker suck?

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Ok. So i made a box thats 12 inches square and about 48 inches long with an 8 inch pipe coming out the top end. I cut it down to about 36 inches. It helped some but not what all the other ones that ive seen are like. Is the box still to long? The end of the box at the fire box is square.  Does it need to be at an angle? Is there a formula of size to length to hight to angle of sunlight coming threw the door? Getting very frustrated. Need some help!!

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Your opening is 12 inches square, going into a 12 inch square box that is 4 feet long, and then up a 8 inch diameter chimney that is 7 foot tall.

The super sucker is basically a 12 inch cube with a 10 inch square opening at the fire, a 6 inch tunnel length, and a 12 inch chimney. 

The BP1048 Hofi Side Draft Chimney is 13 inches x 13 inches with a tunnel is some 4 feet long, a 12 inches diameter chimney, that is 10 foot tall.


The big differences are between a 8 inch diameter chimney (area 50 sq inches) and a 12 inch diameter chimney (area 113 sq inches) or 2.26 times larger. The difference between a 7 foot tall chimney and a 10 foot tall chimney, is 1.42 times taller.

Put another way the chimney is 2.26 times larger and 1.42 times taller. 

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Try not to get too frustrated, or at least know your not the only one who's  frustrated. There are few definite answers in the fluid dynamics of the airflow in a forge chimney as it seems to be effected by the wind velocity of an unladen sparrow.  My understanding is that to get the suck into the supersucker, the design needs to have it's opening at the bottom be smaller than the opening at the top of the chimney. The amount of hot air coming out of the top needs to be replaced. By having the replacement air enter through the smaller opening it has to increase it's speed to match the amount leaving the top. Thus giving you the sucking action. Supersucker design= 12in chimney(113in²) with a 10in x 10in opening(100in²), bottom is ~90% the size of the top. I also heard that a 10in chimney(79in²) with a 8in (50in²) circular opening below works well too, 63%

If you wish to stay at 8in then you would need to make the opening in your supersucker less than 50in², I would suggest between 30-45in² to keep within the 60-90% range. Though I admit that is just a guess on my part

You may want to look into a larger diameter chimney as Glenn suggests. A larger diameter means more air moving and a larger opening, both make it more likely to catch the smoke. Isn't that the goal of a supersucker? Taller chimneys increase draft as well.

Also to maximize the effect the suction has on removing the smoke, you should set the sucker as close as you can to the fire so you get the heat(which keeps the draft going after the initial paper fire inside) and smoke, not just the surrounding air. Especially if you keep the 8in chimney, a 30-45in² opening would have to be right on the smoke to catch it.

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Ok. I think i got this now. So if i stay with the 8 inch the opening would have to be about 7x7. If i go to 12 inch the opening should be about 10x10. Looks like im buying some 6 inch pipe today. Thanks guys. Will let you know how it works. 

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1 hour ago, Ericsg said:

So if i stay with the 8 inch the opening would have to be about 7x7. If i go to 12 inch the opening should be about 10x10.

Go 12 inch, with a 10 x 10 opening. The smaller size might give you sufficient velocity, but probably not adequate volume.

53 minutes ago, Glenn said:

ThHelium Tank Super Sucker was made from an old party balloon helium tank. You can see how much draft it creates.

 Always nice to see your work cited as a (positive) example. 

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