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Alan Longmire ? about Side Draft


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Alan

The post "woeful draw" showing your side draft hood.

 

I finally got some sheet iron to make one.

 

I have a few ?

You said- My setup is balanced to the size of the flue and the firepot.

 

My pipe is 12 in. firepot 8 3/4 in. wide X 10 1/2 long -I would like to blance mine please.

 

The forge the firepot sits in I have a 8in X 23 1/2in. long space to the right ( the left side is way smaller + my blower stands on the left side)

 

I would like the hood to sit on the forge and angle out at the top maybe 13 in?

 

I guess what I need to know is what kind of volume do I need in the chamber?

 

How about my Opening at the firepot- should it be the same area as the 12in. pipe or smaller?

 

I thought I would put a smoke shelf in it also - what little I could find about smoke shelf is the top

of the smoke shelf needs to be no less than 8 in. from the top of the firepot opening.The top of the smoke shelf needs a concave curve bent into it also & the space between the top edge of the smoke shelf and the wall needs an aera like 3 times the aera of the pipe?

 

Do I need a chamber above the fire shelf before it goes in the 12 in pipe - is there a rule of thumb to go by?

 

I dont want to build somthing thats not going to work

Tired of choking down Coal Smoke

If any one can help I would be Thankful

Thanks Ron

Edited by Ron Hicks
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Hey, Ron! :( Sorry I didn't see this before today, things have been hectic around here lately. :wacko:

 

If it's really not TOO too late, it all sounds good but the smoke shelf. :excl: DO NOT :excl: add a smoke shelf, and if you did put one in take it out. They only work in fireplaces, and in a hood or forge chimney all they do is restrict the draw of the stack. The hood itself provides the restriction that produces the venturi effect.

 

Sounds like the volume you have is right on. The opening at the firepot should be roughly the same area as the chimney/pipe, so a 12" opening like you planned ought to work. Don't make it any bigger, though.

 

Good luck! B)

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I will know today hoping to put it together

Heres the size I ended up with

very bottom 7 X 23 1/4

The back is straight to top - 48 in. tall

The front slopes outwards to 42 3/4 from bottom then straight

The sides do the opposite straight up to 42 3/4 then slope inwards to make a 13in. square at top.

Smoke hole is 12 X 12 with about a 5 in. radius in the upper corners.

12 in. pipe

I plan to make some small screw on clips to attach it to the forge

 

This thing will weight a ton not sure the gauge measures 3/32 in.

I bought heads & tails . 25 cents a pound ~ new sheet was over $90.00 4 X 8

 

I know whos making all the money now .

 

What little I have found about side drafts

2 sides ~ One pro smoke shelf and the other No smoke shelf

the ones Ive seen with smoke shelf all were big over 4 ft. and like 15 in. deep

the ones with out were way shorter like 15 +

I think the smoke shelf is for stoping back drafts

 

Ive seen all different sizes small, tall, skinny& fat. One book just showed only a

big pipe with a hole in the side sittin way back from the fire like 8-10 in. I bet just a big pipe

would work pretty good.

 

I think with a box though it would improve with all that air space heating up.

 

Ill let you know how much suction

Ron

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Sounds good! Yeah, the big ones like mine and yours-to-be are a bit of overkill, but there's no such thing as too much suction. ;) The big chamber allows a LOT of room for preheating the stck air column, which allows serious draft inducement. That said, a 12" or larger pipe set right on the forge table with a 10x12 hole in the side will work pretty well too. The idea is mostly to prevent ambient (cold) shop air from being pulled into the chimney until it's gone through the fire first.

 

The pro-smoke-shelf folks are nuts. Okay, insufficiently informed, that's better. :lol: Talk to an industrial fluid engineer about hot air flow sometime and see what they say about introducing obstacles to the airflow path. The smoke shelf has the weight of tradition behind it, but then so does witch-burning, child-beating, and racism. Doesn't make it right, just makes it old and well-used. <_<

 

I've never heard of a side-draft hood getting downdrafted. Of course, some of that is in the chimney cap construction. If you use a stationary pointy cap, allow at least a full diameter's worth of free space between the top of the stack and the cap or once again you're introducing airflow constipation. I have a whirlybird roof turbine vent on top of mine. It keeps out the rain, and as long as you don't melt the bearings it actually increases the draw as it spins! Whatever you use on top, make sure the top of the chimney is at least four feet higher than anything within 40 or more feet upwind. If that's not possible, just make it as tall as you can.

 

I know what you mean about the steel. I got mine at the junkyard for $.30/lb, sounds like the same thickness as yours too.

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Alan

Do I need the little wickerbill do dad above the opening?

If so how far should it stick out?

 

Ive got it welded just need to cut hole and weld on a colar for the pipe- ran out of gas :angry:

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The little whickerbill doodad (neat word! :D ) is not necessary, but I find it helps if your shop is drafty like mine is when I have the big doors open. It seems to keep the smoke going in better on mine. Lots of folks don't have one, though. Mine will also brand you across the back of the hand if you get too close, so you've been warned. ;)

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sidedrafthood1.jpg

sidedrafthood2.jpg

This is my first time welding it squared up pretty good

I thought by angling it out over the fire would help the draft

I was afraid I could not see the fire very well with a short one

thats why I made it 48 in tall.

I guess I could have angled it the the other way with a straight up front.

I need to cut the hole in the top for 12 in. pipe and weld on a colar when I get aceytleen

I may leave the Wickerbill off and try it first

What do you think

Hope it works

Rob

Edited by Ron Hicks
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Looks great! Are you gonna use it outside? If so, a short wickerbill may be needed/wanted, but by all means try it without one first.

 

The only problem it looks like you may have now is figuring out how to rig a screen over the firepot to keep the coal from getting sucked up the chimney! :lol:

 

Throw a lit ball of newspaper in there before you light your first coal fire, just to get the draft going. Or, you can just heat up a chunk of the hood with a torch, that'll do it too.

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Its going in my shed -

Now wouldnt that be nice suckin the coal up the pipe Ha! :lol:

Ill get some pics. when it suckin coal

Thanks Ron

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Archie

I hadnt cleaned out from under the hood very well.

I just stuck a chisel under it to plum it up to take a pic.

I hope its working by the weekend

Ron

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sidedrafthoodworking3.jpgI finshed it up friday just before the ice storm hit-

only built a small fire looks like it will work good

no pre heat it was sucking all smoke, only 3 ft. above peak

will add another 2 ft. -

Thanks Ron

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