Coal Forge Half Hood - how would you build it ?

Billy NY

Well-known Member
I attached some links for reference. I need to build a cigarette smoke vent system. I thought of a "half hood" commonly used on a coal/coke forge. Centaur (see link) has exactly what I need, $239 for the 30" one + oversize shipping. Normally I'd bite the bullet and pay up, however I think its too much and I'd like it to go towards something else needed just as badly. Fixed income, here, never been cheap or all that frugal, but I am sick of having to pay up in excess when I know there has to be a better way.

So thinking about this,(value engineering LOL !) searching the web, I remember corrugated metal pipe we used to install for culverts and the shape of the end piece, the apron, given it has a collar clamp already, I think I can make this work, its $139, no shipping charge, available locally, the shape is similar and more than likely I will have to go for one. The need is of life/safety, as my elderly mother's health is involved here, as is mine as I have to look after her. She's a stubborn cigarette smoker who will not change.

How would you build it from sheet metal ? What gauge? It looks like a not so complicated pattern to cut, bend and fasten the top for an 8" collar, but I am no tin knocker or sheet metal fabricator. I can almost see how the sheet needs to be cut, but what about the top flange for a collar, just make a bend for a connection flange? Think I could do it for less than $139?

The metal culvert pipe apron I could add some sheet metal to make the enclosed part retain the exhaled smoke without spilling out, if necessary, as its darned close in shape and sure looks like the easiest way to get this piece and or something that should work.

I called a sheet metal fab shop, sent an email with pertinent information, photos of half hoods, one looked like a modified hvac duct piece, but I could not pin down what the piece is called, there are so many. In any event, the person on the other end was not so kind to even call me back, after I called in follow up. No one calls you back today, for whatever reason, I get the same thing when applying for work or submitting a resume, that's how it is today. Kinda ticks me off, as I need this thing built and installed yesterday. I've seen 55 gallon drums modified and many variants, but whats in the photo(centaur half hood) would be be perfect if I could make it myself. It will have an 8" fan and 2 90's to get it out through the exterior wall, from there I need to figure part 2 of it to get it away from the house.

I figure an 8" will give me enough CFM, (depending on the kind of fan) with direction changes and transitions. Probably no more than 18'-0" of pipe from the exhaust side and (2) 90's to get to a roof vent, and (1) 90 up just above the hood to the intake side of the fan, just to give some idea of what I plan to do.

Any and all help/suggestions much appreciated, thanks again !!!
Half Hood

8
 
I had one made from the discharge chute system of an old chain flight farm elevator. The chute usually ended up round for the attachment of a swivel chute. Look over the arrangement...lots of those old elevators sitting in the farm groves out here in Iowa but I have none I could photograph at the moment. Leo
 
for this application have you checked out range hoods at the big box home improvement stores? home depot, lowes, menards, ect. should do what you need for less than $100.00
 
I suggest getting a copy of SMACNA'S Industrial Ventilation manual. It will explain how to properly design and ventilate a hood. More to it than you think. The manuals are on Ebay all the time.
 
If I were going to make one for your purpose I would form it out of light rigid plastic sheet. No need to be steel for cigarette smoke.
 
from the look of the half hood you need a square to round fitting with the round offset to one side. 18 gage metal should work for the rigidity. Then just cut away the metal you don't need. Your problem may be that like a lot of small shops they don't know how to layout the fitting. A commercial shop would have the qualified layout man or a computerized plazma table and could do it easily. By hand it would take about a hour. Plazma table would cut it out in a matter of a minute or so. The problem is stopping production for a one off piece can get expensive.
Angle Iron
 
I have a forge that I built years ago. I would have to look at it to remember what I used as the hood but it is some pretty heavy steel. Have a true hand crank forge blower for it to boot. Uses 5 inch well pipe for the smoke stack
 
Would this work?


http://www.ebay.com/itm/30-Stainless-Steel-Kitchen-Powerful-Wall-Mount-Range-Hood-Vent-Touch-Control-/131207197846?pt=LH_DefaultDomain_0&hash=item1e8c8ef496
 
something to think about. It took me 5 years to do a total remodel and double the size of my home. Boss wanted a gen-air in center island of kitchen. It has a 5 inch power vent in center of stove. When we turned it on, it would pull the exhaust from gas furnace down the chimney in to the basement. So when we would use the vent, we would have to open a kitchen window. In the winter, a ton of very cold air came in the window.

Think about it, every cubic ft of air you remove from house has to come from some place.

If your mom smoked next to a gen-air, there wouldn't be a problem, the vent fan could suck it out.
 
How about a straight register boot? I think you can get them as small as 4" diameter for the round part.

Dusty
 
I looked at those, definitely a consideration, might have to take a 2nd look, one thing is for sure, it don't have to be fancy, just work is all LOL !
 
Yes, excellent point! Well aware of make up air, and in some situations that could be a problem like you describe. Buildings are or can be pressurized, so when you alter or change that, things change. I was a project manager in the commercial construction industry, high rise, mid rise and all sorts of other kinds of buildings and occupancy classifications, had a lot of exposure to the associated HVAC and MEP systems, make up air is usually designed into the building somewhere.
 
I believe it would, and I think I'd add 3 sides to it that extend downward, and the sides would be tapered like a half hood, just enough to better retain the exhaled smoke, you'd think the fan would be adequate.

The only drawbacks with one of these, well that one is reasonable, most are $400 or more, so you found a lower end model, and for some reason, every one I looked at was in the above price range. The other concern is distance with changes in direction and these are 3" or 4" exhaust if I recall. It may not pull enough at the suction end. I've read about cigar room ventilation and 6" systems in some cases were disappointing. So I decided maybe I ought to just go for an 8" design, and possibly transition to 6" after it exits the through the exterior. I would imagine there is a simple calculation, include size changes, 90's 45's etc, and you could determine what CFM you then have.

That's my concern, that I undersize it and it does not perform like I want. Given where I need to route this, I figured base on cost, it would not hurt at all, 8" inline fan I can get from a supply house for $50, duct is cheap enough. Range hood is really what I thought of at first too.

I suppose the reason I am being more frugal than usual, is I have 2 bathrooms that need upgrades, shower and bath enclosure, + several other small repair jobs, most of which I can't reduce costs on, so this job, I figure there has to be a way to minimize the cost. Its important health wise, as her being elderly, and the position I'm in with all of this having to keep tabs on her, I just can't have that smoke in this house, push comes to shove, that will over ride any budget considerations.
 
Rich, I've seen a few over the years, as we've always hired out blacksmith and horseshoeing work. Interesing what people build for one. Going back to the early 70's, one blacksmith we had, used a coal forge in his van. He used an old beer keg as the fire box, smoke pipe at the top of it and routed through the roof of his dodge van, and what seemed to be a blower motor, like from heater box in a car or truck, squirrel cage or turbine like fan. Darned thing worked great, and I assume as he made his rounds the coal fire stayed lit from stop to stop.

Whats in the photos below, the centaur 30" is perfect, I'm sold on it, but not the price LOL!

But like you, with say some of the things you've built, from salvage, works as you need, did not break the bank and you can kind of boast or be proud because you defrayed the cost and put it towards something you can't find a way to do same.

PS, sorry to hear about that finger and that N series tractor, sounds like you got ahead of yourself and it bit ya, darned tractor LOL !
 
I agree, its almost possible I could lay something out and cut same, take it from there, but I have to wonder how many sheets it would take before I got it LOL ! I don't mind doing that, would be great to learn too, but this place I called and emailed information to, just blew me off and they advertise, if they can't get it, they can build it and or similar. I looked at eccentric like, and or round to square, my eyes got tired at looking trough 80-100 page catalogs. I was all over finding something close and then modifying it to work, came up with nothing, except what you mentioned, and like what was said below, register boot, which I think I ought to look at a little more closely.
 
You are right, I don't know much about the material, but being a sheet good, I assume its possible to fab something up just the same, really no heat involved here.
 
I could look at those a little more, but I have a few concerns, all the ones I saw were $400, and there is the CFM's I need per the distance and direction change etc., One of these was literally what I first thought of though.
 
I'd be all over something like that, from a salvage pile or fence row etc. Somewhat of an odd shape and size, but thats the fun in things like these, when you find something you know will work, but won't cost much at all.

I was thinking well what about a wash tub, 55 gallon drum, fire place ash bucket, cut out and flange for connecting pipe.
 
That sounds like a great reference book, thanks for the tip, probably is to HVAC what the AISC handbook is for steel, very handy information.
 
The forge I built we used a brake drum out of a big rig for the fire box. Makes it easy to hook up the blower due to the center hole and lug bolt holes
 
Some commercial buildings like schools, bringing in fresh air is needed. But in the winter the cold air will lower relative humidity to desert like. Static electricity, nose bleeds. Summer time you are bringing in loads of moisture.

Get you mom a gen-air range. You can open a window in any part of your house, turn fan on and feel the breeze coming in the window. Or send your mom to the bathroom to smoke. Kids do that at school. Girls are worse than the boys.
 
Billy; In your response to Angle Iron below you wondered how many sheets of sheet metal you would go through before you got the shape right, but you don't have to use sheet metal for a pattern. Cardboard would probably work fine. Get the shape right with cardboard or some other cheap or free material, then use that as your pattern on the only piece of sheet metal you should need. Only if you want to cut it yourself, of course.

Stan
 

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