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Hofi Hood


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It doesn't look like the Blueprints are up...that or my computer wouldn't pull them up.

Anyway, the specs are 14" square and as long as you need to get it out the wall and allow enough room outside to put a 12" pipe in.

I'm not sure if there are any specs for the angle on the forge side of the hood but I did four inches so that the top plate of the hood was 4' 4" and the bottom plate was 4'. There are several pictures of my hood on the third page of the forge build thread that I posted on your forge thread.

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what do you mean by cap, like a rain guard on the top of the chiminy, also im looking for more of the links that you gave me unforgivn. the flue and chiminy i kinda got the basic idea for my needs, i need to go straight up, i dont have the option to go out the side of the shop just up, im needing a good design for the acctual hood. Thank you both.

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Another question i just thought of because something i read, does the drafting of the air have anything to do with heat, i read on anvilfire that sometimes you need to throw some sort of flame in there to get the draft going, also (im sorry for so many questions, my mind works to far ahead of its self) with the anvilfire hood designs whats with the dashed lines inside of the main design.

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Technically there is no Hofi Hood, if you want to go through the roof rather than the wall that is fine, do it that way.

Hoods are notorious for not getting all the smoke, because of all the room air going up the flue as well, unless it has a very large exhaust fan. the side draft works a bit better at this.

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I would highly recommend a rain cap. Especially if you are going straight up.

Don't worry about asking too many questions! That's how you'll learn...that's how I learned.

The type of hood in this link is great! They have these at the John C. Campbell folks school and they work very well. The dotted lines show the position sheet steel smoke shelf that is inside the hood. This type hood would work great for the size forge you are building, but the cost of fabricating this large of a hood is higher.
http://www.anvilfire.com/21centbs/planfile/

This is the super sucker. The dotted lines in the front view simply show the outside sheet metal along the sides. The super sucker in that design has a flange all the way around so the sides are inset. Those dotted lines are there just to clarify that. This is probably your cheapest option.
http://www.anvilfire.com/21centbs/planfile/

As a good alternative you could do like the picture of the ABANA set-up. check out "John McPherson's" post (post #6,) in this thread. All it is, is a piece of culvert pipe (12" or 15") with a hole cut out of one side of it. The shop doesn't look smokey! Culvert is expensive, but it's a one stop shop. You have a "hood" without any fabricating, and you have a pipe too.
http://www.iforgeiron.com/topic/22955-why/

Draught is affected by heat. When you start your fire, throw a piece of burning paper in your hood and it will get hot air moving upwards.

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Sam,

I would suggest the "super sucker" design as depicted on Anvil Fire website. It will allow you to use a 10 in pipe and the design is very efficent. Pay attention to the number of elbows you have in the set up , less is better. Make sure you get enough stack height for the building"s configuration.

I built this unit depicted below and it works very reliably in all sorts of weather conditons.

Good luck.

Peter

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Mr. Peter, you have an awsome set up! So neat and tidy! Is it still so tiddy after a little bit of use? :) (I seem to recall you built this one about time I installed my forge?)
I've got a second forge I'd like to put in who-knows-when, and I think I'm going with the super sucker then as I'll be going straight up. What gauge SS is that for the smoke stack?

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Fiery,

Thanks for your kind comments.

There is two parts to the duct system for the forge. The portion inside the building is just galvy 10 in. ducting. The heat is not an issue so go with whats available at the building supply store. You could use HD stove pipe but its overkill. Once I got to the bulkhead penetration I went with metal-bestos insulated 10 in stove pipe, rated for 2" clearence. The cost is obviously higher but this does protect the building and in some areas it is a code requirement. Additionally, if you have to move the shop, the (expensive) pipe is modular and you can break it down and take it with you to another location.

One design consideration worth discussing. Set up the forge so that you can move it around to accomodate long sizes of stock. Right up against the bulkhead or in a corner is convient for a flue connection but it's length limited. I just did a commision for a house on the coast of Maine. It was a hanging pot rack system for a fairly large kitchen. The shortest run of stock was 10 foot. If the forge table is movable you can shift it around as required. The relatively light weight 10 in ducting is quite flexable and this works to your advantage. The best shops I have seen are the ones that are built in a modualr fashon. If you want be able to use floor space, your gear has to be movable.

As I recall the forge table stayed clean for about a day.

Peter

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Petere76 I like your hood and that was the style i was looking into makeing, how im going to get the money for the steel i have no idea. What thickness did you use? Also a more important question that might help me out alot in designing this is, how dose a super sucker hood work, do you need an exhaust fan? Also my forge is going to be like yours but sideways. Imagine your forge lengthwise with the pot in the center. Its some sort of table that i got and has a big lip on one side, the long side. so i thought to make it with alot of room to each side of the firepot rather than in front. Granted the forge will be in a cornor but i dont know how else to do it. this is a big project to me and i dont want to mess up like i did my first forge that has had many remodles. but i want to make it so it will be a permanent forge. it has a 5/8 fire pot 1/4 steel table with casters. all i need is a hood and a blower set up and im good to go. just have no money. so any more advice you would be willing to share would be much apreciated. (also i would load pics but i cant seem to send a message to gleen to figure out why)

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Hey Sam,

the SS hood ia essentially a elbow box transition with a slanted face plate. It connects serves to redirect the smoke and connects to the uptake. the magic, if there is any, is that the opening (square inches) of the front face must be less than the opening of the uptake pipe (square inches). The venturi effect of the larger uptake and the smaller opening combined with the heat of the smoke make it all happen. Measure your pipe and size accordingly. My forge uses a 10 inch pipe with a 3 elbows. The suction is fine in all manners of inclement weather and cold temps. I fitted a sliding closure on the front to keep out the Maine -20 F winters and the critters when the forge is not fired. You may want to consider a similar fitting.

The table configuration is really up to you and whatever works in your shop for the sort of work you do. If you work with long stock obviously the corner is not a good idea unless you have a window or door on the other side. I prefere modualr shops so that the equipment can be moved about to accomodate different jobs. You can run stove pipe quite a distance horizontally and still get decent draft. As your table is on wheels you already have a little bit of flexibility going for ya.

Dont worry about messing up, thats where we all learn the most. Better to try and fail a few times than never try at all, right. The fellas on here have all sorts of experience in almost anything you want to do. Great ideas are as they say, where you find them. You will do fine. Good luck.

Peter

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Peter could you give me a bit of a better explination on the matmatics with the square inches of the uptake and opening, also what about the elbows? i was told that was a no no. I have to go straight up so if your talking about an elbow out the wall thats not an option for me. with the super sucker do i need a smoke shelf, and what is a smoke shelf? Ok now that i have those questions out of the way i want to say that with my forge build im seting it up so that the main pieces are the hood, firepot and blower set up. im going to keep the peice i cut out for the firepot so if i ever have to re designe i reweld it in and am good to go. the most i will need for length in stock is about 3 feet which i can manage. i plan to move my forge set up a bit diff to give me more room and make it out the roof easier. And honestly to you all if i dident have your help i would be totaly lost. thanks all.

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Sam,

The math is a straightforward calculation of the opening square inches. 10 in pipe is @78.5 sq In, knowing the stack opening, you size the opening of the hood face to be slightly less in total square inches (length x width).

In so doing you are creating a slight venturi effect at the opening and this aids in maintaining a negative pressure (draft) . This effect combined with the physics of warm gasses of combustion occuping space and moving up the stack as a mass maintains the flow. Its essentially a mass flow device governed by the relationship of mass and acceleration. (F=M x A). In my case I have a cover which slides over the opening so the size is variable but I never really need it because the draft is substantial and consistent. Mostly it keeps the citteres and the -20F winters outside the shop.

Elbows, rough pipe and the cap configuration only serve to "reduce" the flow by increasing the overall resitance. These are on the loss side of the flow quation. You are actualy trying to maintain what is called "laminar flow" of the gas. Turbulance is not your friend in these (natural) type systems.

Postion of the uptake and its relationship to the roof peak is important. My set up is exterior to the outter wall. I use a 10 in pipe with 3 transitions (two inside and one outside) , a mushroom cap and a relatively short exterior 10 in insulated stack. My set up works great for this location and this particular roof pitch. Its important to design and build for your particular location and building configuration. Do your homework, read up on chimney construction and placement, that will give you the basics and you can move forward from there.

Good luck with your project.
Peter

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Sam,

The math is a straightforward calculation of the opening square inches. 10 in pipe is @78.5 sq In, knowing the stack opening, you size the opening of the hood face to be slightly less in total square inches (length x width).



I just did the above Sam, based on Mr. Peter's shared knowledge. The wall next to my forge is still open and I get a lot of wind that tears my draft up pretty good, but this modification made a marked difference in pull. I had a reducer made but it was too small. It took about 15 minutes to modify it. (And we are closing that wall up today! :D)
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