Ventilation - How to. I need some good help / advice

[Avadon]

Hello Everyone, I'm calling in help from the pros once again.  ;)

What is the best method(s) for ventilating a smithy?

 

It's a 24'x30' existing shop and I intend to have two forges in there and do smithing/welding.

 

Some questions:

I know colleges have point exhaust systems for welding. Where can I buy a point exhaust system for all my tig welding? Is it practical to build one? I'm trying to stop having to always exchange all the air in the shop, especially during cold winters/hot summers where I have to recondition all the air coming in.

 

The shop has staggered stud walls and furred out trusses to 2x6's. It has 6 existing roof vents, which are about 10"x10" openings. What should I do with these. Box them with lumber so we can spray foam around them?

 

they look like sorta like this

 

Outside of a point exhaust I'm thinking of a way to exchange the air in the shop with significant volume and speed for times when I really need to push everything out quickly. I did this in my old shop with strong cross ventilation. It would suck from storm windows and blow out through others but I don't have that luxury anymore.

 

I'd like to have the walls of the shop fairly closed up to take advantage of my sound suppression. So I'm thinking I need some sort of baffled/insulated intake so I can bring fresh air in and then blast it out of the roof. Would I be best off taking the vent in the middle of the roof, enlarging it, and trying to mount some sort of high power exhaust fan under that vent to pull all the bad air up and out?

 

I thought about making some hoods over the forges but with my rafters spray foamed I'm thinking everything will just go up to the ceiling anyway. I'm going to spray foam the rafters and put 2" of rigid foam over the rafters. Do you really gain anything from hoods and exhaust conduit? Since everything is sealed I just figured all the smoke would pretty much funnel to the top of the inverted v shape anyway.

 

Also:

 

Where should I position an intake(s)?

 

Should i mess with air exchangers?

[BobL]

Do you really gain anything from hoods and exhaust conduit? Since everything is sealed I just figured all the smoke would pretty much funnel to the top of the inverted v shape anyway.

 

If you hope everything will just go up to the top of the inverted V then you will be disappointed as the "stuff" will diffuse all over your shop about as quickly as it rises. You may not even see what the stuff is as most of it is invisible to the naked eye but it will be there and heaps of it. Hoods and exhaust conduit create a much higher air speed with a specific direction than simple bulk rising thermals. The faster the air stream the more it can carry before the heavier gunk has time to settles out. I'm not talking metal chips here but pretty well everything 

 

I have a 500 cfm fume hood under which I try to do as much metal work as possible. This helps reduce the level of grey goo that normally settles all over my small shop during metal working. I'm lucky enough to have a laser particle counter so I can routinely test my shop air. I normally use this for wood dust assessments in hobby type wood workshops but I have used it to test my shop air during metal working and it gets pretty bad unless I have my fume hood operating.

 

I also have a fully ducted  1250 cfm wood dust extractor system that also extracts to outside my shop (it rarely gets cold but I do lose my air conditioned cold air in summer) but I don't use this for metal work as it will block my wood dust extractor filters with "grey metal goo".  

 

BTW I also have flow testing gear and have tested the flow rates of a range of dust extractors and fans and the manufacturers ratings are almost all incorrect by at least a factor of two (2 times higher than they really are) and by the time ducting and filters are added it can be more than a factor of 6. 

[ThomasPowers]

What type of forges?  Induction forges don't require ventilation.

[Robert Yates]

For a direct Ventilation a semi-flex hose with a hood or canopy over the welding station powered by a small/ medium size squirrel cage motor ( they are cheep,quit and good for this application) or a good High dollar Bathroom vent to remove the welding fumes . as for fresh air circulation you can instal a ceiling fan and a Box type fan in the gable(make sure it is installed so it will pull the air out or supply air into the shop ) with duct work and a return cover in the ceiling . knowing what type of forge you have (even photos of the shop set up would help us recommend a better solution for you .

 

Sam       

[Avadon]

How big of hoods do you suggest for propane forges? Should hoods be small like 2' x 2' or are they better off large like 4'x6'? is there some equation I need to know?

 

As for the point exhaust for welding would something like this be any good http://www.ebay.com/itm/350252094762?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649   it says it's 449 CFM.  I had a hard time trying to find anything more powerful without really breaking the bank. A lot of those point extraction arms are really expensive.. like $1200 and that doesn't even come with a fan, or filter.

[Avadon]

What type of forges?  Induction forges don't require ventilation.

 

Propane gas forges. :)

[Avadon]

For a direct Ventilation a semi-flex hose with a hood or canopy over the welding station powered by a small/ medium size squirrel cage motor ( they are cheep,quit and good for this application) or a good High dollar Bathroom vent to remove the welding fumes . as for fresh air circulation you can instal a ceiling fan and a Box type fan in the gable(make sure it is installed so it will pull the air out or supply air into the shop ) with duct work and a return cover in the ceiling . knowing what type of forge you have (even photos of the shop set up would help us recommend a better solution for you .

 

Sam       

 

I was trying to find a good semi-flex hose that didn't cost a million dollars. Do you know of any good semi-rigid hose you can use without having to shell out $1200 for a point extraction arm?

 

I know what you mean, I may have to get my shop almost completely finished before I analyze what is the best way to ventilate as it does get a little complex when you think about where to draw from, where to exhaust to, etc.

 

Shouldn't a fresh air intake be somewhere low towards the ground so it's not mixing with bad air that may be up near the top of the rafters? Or are you more like talking about pulling air from one gable end and pushing it out the other. That would be a good idea, but one of my gables is attached to my house so I can't bring fresh air from one side nor exhaust bad air on that side.

[John McPherson]

The roof vents from the stock photo posted are just to keep your roof from overheating in the summer, and the attic space from mildewing in the winter. They are not for human comfort, and blocking them will cause problems. Combined with soffit vents under the eaves, they are an example of high/low passive ventilation.

 

The government has established limits regarding Manganese, Chromium and particulates for commercial shops. They seem to get tougher every so often. Ignore known risks at your own peril, but exposing others creates liability.

 

Yes, our college shop has really big articulated fume extraction arms over each station, that dump all the air outside. They draw so hard when all three bays are on, the shop doors are hard to open or close. We have a big downdraft grinding booth, now relocated under an awning outside. The CNC plasma cutter has an adjustable water table to trap most of the particulates, and muffle the noise and light.  Manual plasma cutting and carbon arc gouging is done outdoors, weather permitting. It is still not enough to remove all of the haze, and prevent a coating of dust from settling on every surface, including the walls. What it does do is keep it to a more manageable level.

 

Looking at what is commercially available (red, blue, yellow) from your local welding supplier would be a good place to start. The $1200 does not seem unreasonable for what you are getting. Decent industrial filtration and air handling does not come cheap, and DIY comes with a steep learning curve.

[Mainely,Bob]

Some points to consider here. First is that propane forges (or any heat source that draws air in order to burn) also  consume the same air you need to breathe. Where is that air going to come from if your shop is sealed up tight?

The second point is one that most folks miss as well. Metal, especially metal we intend to forge, is rarely "clean". Put metal into an induction forge and it most likely will give off some kind of smoke and/or fumes, even if it`s just from the residual things like oil from our skin, our gloves, that oil  you didn`t fully wipe off the bench from the last project because you reasoned it`d help keep the bench from rusting, etc.
I have seen some of your projects Avadon and like me you take pride in smoothing and grinding things so they flow nicely. That grinding dust also needs to be dealt with and it`s not the kind of thing that rises like smoke and fumes. It requires point capture and something more akin to a shop vac rather than a passive system or ventilation fan.

 

  There are factors in play here such as floor plan, type of work, square footage, wall as well as overhead construction that we need to know about before we can give you detailed info. I know you like your answers to be as defined and polished as your projects so help us by taking the time to give us all the info you can pertaining to your work and environment as well as pics. As you know, Frosty isn`t the only one who loves pics. :)

[Avadon]

Some points to consider here. First is that propane forges (or any heat source that draws air in order to burn) also  consume the same air you need to breathe. Where is that air going to come from if your shop is sealed up tight?

The second point is one that most folks miss as well. Metal, especially metal we intend to forge, is rarely "clean". Put metal into an induction forge and it most likely will give off some kind of smoke and/or fumes, even if it`s just from the residual things like oil from our skin, our gloves, that oil  you didn`t fully wipe off the bench from the last project because you reasoned it`d help keep the bench from rusting, etc.
I have seen some of your projects Avadon and like me you take pride in smoothing and grinding things so they flow nicely. That grinding dust also needs to be dealt with and it`s not the kind of thing that rises like smoke and fumes. It requires point capture and something more akin to a shop vac rather than a passive system or ventilation fan.

 

  There are factors in play here such as floor plan, type of work, square footage, wall as well as overhead construction that we need to know about before we can give you detailed info. I know you like your answers to be as defined and polished as your projects so help us by taking the time to give us all the info you can pertaining to your work and environment as well as pics. As you know, Frosty isn`t the only one who loves pics. :)

 

Thanks for the compliment. I never really thought of putting a point exhaust at my KMG grinding station but I think that is definitely something to consider for the future. I don't have any pics of the finished shop yet because I'm about 80% through construction. Finishing walls and getting ready for spray foam this summer. I definitely understand what you mean about 'sealing it up tight' as yes you'll burn through the oxygen needed not only to breath but for the forge. I think my idea of "tight" means without sound escaping. I definitely need a large clean air draw but it will have to have an STC rating. So it will have to be some sort of inlet that channels through something like a sound isolated stack. I'll have to do more research on that. I guess one of my primary questions is should fresh air be drawn from low on a building, or on the side of a building or from the roof, or does it even matter?

[Frosty]

I've been reading rather than hopping in on this thread. Last time I recall the forum has at least one professional ventilation expert, whatever they're called and I was hoping they'd jump in. <sigh> So much fore hope.

 

I've laid out my downdraft floor gozinta system but that's not a possibility unless you want to start digging up your floor. The downdraft welding/cutting table is still possible, no hood and no escaped smoke/fumes, etc.

 

Keeping the warm/cool air in while providing adequate CFM for clean air is a problem here as well. One method I've provided for in a limited area is simple ducting running to an exhaust blower and "T"s at satation locations. Opening or closing exhaust at station is as simple as pulling a cap off a "T" and sliding the duct inlet necessary. Some inlets are hoods but most are flex duct as seen on clothes dryers. The outlet from the shop is a basic home made heat exchanger. the air blown from the shop goes out in 8" galvy ducting through 12" galvy ducting. As air is blown from the shop makeup air is needed and it is drawn in through the 12" ducting the 10" exhaust ducting is encased in.

 

Warm air out exchanges temp with cool or COLD air coming in. I've planned a pretty long run for this part of the exhaust system because I don't want to spend the money for a heat exchanger vent system with the capacity necessary. So, I'll trade off the heat savings for the money and CFM exhaust. this system is in the enclosed bench work area Deb and I will be working on copper, silver, etching, pickling, enameling, etc. more fumes of higher toxicity than the general hot shop, Fab, forging, etc.

 

the main floor of the shop has the down draft gozinta system using the shop floor as a thermal battery. Main makeup air will come in behind the wood stove and be distributed via fan.

 

That's my plan I'll have to see how it works and report back. Feel free to use any of it you think my work for you.

 

Frosty The Lucky.

[Avadon]

Hi Frosty.. Thanks for chiming in here. What I asked in our emails about hvac was for the new shop I want to build 36x68 but I'm having curious moments about my 24'x36' existing shop. As it is staggered stud I am trying to think ahead if possible so I don't have to go and rip out studs and expensive spray foam later on.

 

I think welding downdraft tables are great, but I think I'm going to skip buildilng one in this life, I have way to many other projects and I think a point exhaust is probably good enough to vacuum out the fumes. Most of my work is pretty clean. Tig is pretty clean. Often if I'm going to weld on something painted or really grimy I will take it outside and weld on it during the day and let the massive amounts of smoke fume off of it.

 

I do like your heat exchanger idea though.

 

Some of the questions I still have are..

 

What is the best place to locate a clean air intake? low or high on a side of a wall? or on a roof?

 

What should I weld hoods out of and how big are traditional hoods over a gasser? -and how many CFM should i be looking at to draw the bulk of those gasses off?

 

Is there anything better than dryer-type ducting at home improvement stores out of which to build a point extraction arm?

 

 

If anyone knows good answers to these questions I'd love to hear them. I definitely am on board with circulating the all the air in the shop as well as having point extraction at places where welding, sanding, and forging is being done.

[Frosty]

I only mentioned the downdraft floor and tables because I have them and get them out of the way. The first downdraft cutting/welding table I saw was connected to the exhaust system via a long flex hose so it's not out of the question if you wanted to go that way.

 

The heat exchanger make up air system is pretty standard HVAC tech, my boiler is set up with one as are most modern vents. I just adapted the idea to my shop and cheap Scott nature.

 

I like my makeup air intake under the eaves to keep it out of ground effect dust, blowing snow and rain. With my version of heat exchanger I'd have to give thought to how best to get the exhaust are enough away from the intake. Just a detail to think out.

 

I don't usually make hoods out of anything but really thin sheet unless a customer insists it needs to be heavy gauge. 20 ga. is usually way more than enough to direct smoke and warm air. If heat warpage is a factor, thicker or Stainless is in order. Stainless is a better IR reflector.

 

I don't know of anybody using an exhaust hood over a gasser so I can't say how big. I'd have to start asking schools that feature forging and hope to find one using gas forges. My high school had gas forges but the hood covered an area probably 30' square and could suck your hair off. Calculating FM would be a matter of calculating how much volume of superheated gas the burners werre producing and figure a safety factor of at minimum 2x, maybe 3x.

 

I have a friend who teaches casting and holds clinics at colleges, maybe he'll know where to start and who to ask.

 

I don't know just what you want from a point extraction system. Does it have to be an arm? How long? What CFM does it have to carry? What temperature will it need to withstand? More than one? How many?

 

Man, I gotta stop or I'll be asking specific questions when I really need to establish some basic function parameters.

 

Frosty The Lucky.

[Mainely,Bob]

 

 

Some of the questions I still have are..

 

"What is the best place to locate a clean air intake? low or high on a side of a wall? or on a roof?"

 

 Think about the nature of air (what it does naturally as it is heated and cooled) and then think about what you want the air to do for you in relation to it`s nature. This will tell you how you need to move it and what, if anything, is going to be required to move it to meet your goals/requirements.

 

 

"What should I weld hoods out of and how big are traditional hoods over a gasser? -and how many CFM should i be looking at to draw the bulk of those gasses off?"
 

  Answer the first question first. A stationary hood in the overhead that uses natural draft will need to be larger and positioned differently than something like two smaller point capture suction hoods/cones positioned close to the front and rear of your forge. That stationary hood will also require you to keep the forge in one place rather than let you move it  and the blowers if need be.
 

 

"Is there anything better than dryer-type ducting at home improvement stores out of which to build a point extraction arm?"

 

Why limit yourself to home improvement stores? I live on a peninsula and have to drive at least an hour to get to a city and most things I need. Well worth the time and effort to get what is really needed rather than settle for less and wrestle with the shortfalls every day I work with it.

 

 

If anyone knows good answers to these questions I'd love to hear them. I definitely am on board with circulating the all the air in the shop as well as having point extraction at places where welding, sanding, and forging is being done.

[BobL]

What is the best place to locate a clean air intake? low or high on a side of a wall? or on a roof?

 

What should I weld hoods out of and how big are traditional hoods over a gasser? -and how many CFM should i be looking at to draw the bulk of those gasses off?

 

Is there anything better than dryer-type ducting at home improvement stores out of which to build a point extraction arm?

 

 

If anyone knows good answers to these questions I'd love to hear them. I definitely am on board with circulating the all the air in the shop as well as having point extraction at places where welding, sanding, and forging is being done.

RE: What is the best place to locate a clean air intake? low or high on a side of a wall? or on a roof?

If you want to maximize air exchange within a shop more than one intake should be used with most of them as far away from the exhaust as possible. If they are too close to the exhaust the air will come in and go out too quickly without properly venting a shop

if you want to focus on providing clean air for the operator and the operator spends most of their time in one area then the intake(s) should be such that they forms a line between the operator and the exhaust.

 

RE; What should I weld hoods out of and how big are traditional hoods over a gasser? -and how many CFM should i be looking at to draw the bulk of those gasses off?

 I reckon using what you have to hand is a reasonable way to go. one of the most effective hoods I have seen on a forge was made out of kerosene cans.

I used the left over mini corrugated iron cladding I used for the interior of my shop. 

 

RE: Is there anything better than dryer-type ducting at home improvement stores out of which to build a point extraction arm?

Before I had my fume hood I used to vent my shop while stick welding with my $100 wood work dust extractor and 4" PVC storm water ducting. As a point extractor I used a 10 ft length of transparent PVC 4" flexy ducting suspended from a wire between two walls of my shop. The wire and flexy traversed across the top of my small metalwork bench and I could slide the flexy along the wire to get it directly above the work. At first I was very conservative as to how close I would let the end of the flex get to the work but I quickly noticed that (especially at night) the transparency of the flexy enabled me to see how far the sparks would get down the duct but in was never more than a ft at most as the rush of air seemed to cool them down rapidly.Sure the flexy got a few holes and charred marks but it worked well for 6 years and had plenty of life left.  A few times I thought about including a metal chip catcher between the flexy and the dust collector (which was outside my shop) but I never bothered because my dust extractor was so weak (1HP) that a lot of metal dust never would settle out in the flexy so every few months I had to take it down and empty it out. The other thing that the welding fumes did was gum up the extractor bags so they had to be washed more often than I liked which is why I decided to make a fume hood for my new shop.

 

You could use a combo of both the dryer metal type ducting for the first couple of ft and then PVC after that

 

BTW most conventional dust extraction units simply cannot pull more than about 400 cfm through 4" ducting.

6" ducting can carry ~1250 cfm BUT a 3HP or greater motor and 13" or greater diam impeller is also needed.

OTOH using 6" ducting on a small dust extractor will result in the dust settling out in the ducting as happened to me above

 

There is a very instructive chart/graph around on the web that shows what CFM can flow through what diam ducting under what pressure. I have measured the flows through a lot of ducting and blowers and this chart has rarely been wrong. Anyone contemplating setting up a ducting system should really study this to see what is possible and what is not. 

[JNewman]

Having enough makeup air cannot be emphasized enough.  When I was at Touchstone a year or so after they built there blacksmith shop if the exhaust fans were turned on without the doors open the shop would end up with a ton of smoke inside because the coal forge hoods would not draw even though they had a power exhaust on them.  The college shop at Sir Sanford Fleming has a similar problem they only have one or two coal forges and fan on them is so powerful it literally will suck coal up the chimney.  They had to put a fan that powerful on because they don't have enough makeup air. 

[Avadon]

I only mentioned the downdraft floor and tables because I have them and get them out of the way. The first downdraft cutting/welding table I saw was connected to the exhaust system via a long flex hose so it's not out of the question if you wanted to go that way.

 

The heat exchanger make up air system is pretty standard HVAC tech, my boiler is set up with one as are most modern vents. I just adapted the idea to my shop and cheap Scott nature.

 

I like my makeup air intake under the eaves to keep it out of ground effect dust, blowing snow and rain. With my version of heat exchanger I'd have to give thought to how best to get the exhaust are enough away from the intake. Just a detail to think out.

 

I don't usually make hoods out of anything but really thin sheet unless a customer insists it needs to be heavy gauge. 20 ga. is usually way more than enough to direct smoke and warm air. If heat warpage is a factor, thicker or Stainless is in order. Stainless is a better IR reflector.

 

I don't know of anybody using an exhaust hood over a gasser so I can't say how big. I'd have to start asking schools that feature forging and hope to find one using gas forges. My high school had gas forges but the hood covered an area probably 30' square and could suck your hair off. Calculating FM would be a matter of calculating how much volume of superheated gas the burners werre producing and figure a safety factor of at minimum 2x, maybe 3x.

 

I have a friend who teaches casting and holds clinics at colleges, maybe he'll know where to start and who to ask.

 

I don't know just what you want from a point extraction system. Does it have to be an arm? How long? What CFM does it have to carry? What temperature will it need to withstand? More than one? How many?

 

Man, I gotta stop or I'll be asking specific questions when I really need to establish some basic function parameters.

 

Frosty The Lucky.

 

 

Yes if you know anyone who knows the answer to the forge hood size question that would be great.

 

In a point extraction system I need something at least that can hold it's shape and be positioned around a 4'x8' area and suck up TIG fumes. It doesn't need to withstand high heat. But I think I have to stay away from any plastic components. - And I only need 1 extraction point for the welding.

[Avadon]

I only mentioned the downdraft floor and tables because I have them and get them out of the way. The first downdraft cutting/welding table I saw was connected to the exhaust system via a long flex hose so it's not out of the question if you wanted to go that way.

 

The heat exchanger make up air system is pretty standard HVAC tech, my boiler is set up with one as are most modern vents. I just adapted the idea to my shop and cheap Scott nature.

 

I like my makeup air intake under the eaves to keep it out of ground effect dust, blowing snow and rain. With my version of heat exchanger I'd have to give thought to how best to get the exhaust are enough away from the intake. Just a detail to think out.

 

I don't usually make hoods out of anything but really thin sheet unless a customer insists it needs to be heavy gauge. 20 ga. is usually way more than enough to direct smoke and warm air. If heat warpage is a factor, thicker or Stainless is in order. Stainless is a better IR reflector.

 

I don't know of anybody using an exhaust hood over a gasser so I can't say how big. I'd have to start asking schools that feature forging and hope to find one using gas forges. My high school had gas forges but the hood covered an area probably 30' square and could suck your hair off. Calculating FM would be a matter of calculating how much volume of superheated gas the burners werre producing and figure a safety factor of at minimum 2x, maybe 3x.

 

I have a friend who teaches casting and holds clinics at colleges, maybe he'll know where to start and who to ask.

 

I don't know just what you want from a point extraction system. Does it have to be an arm? How long? What CFM does it have to carry? What temperature will it need to withstand? More than one? How many?

 

Man, I gotta stop or I'll be asking specific questions when I really need to establish some basic function parameters.

 

Frosty The Lucky.

 

 

Yes if you know anyone who knows the answer to the forge hood size question that would be great.

 

In a point extraction system I need something at least that can hold it's shape and be positioned around a 4'x8' area and suck up TIG fumes. It doesn't need to withstand high heat. But I think I have to stay away from any plastic components. - And I only need 1 extraction point for the welding.

[Avadon]

 

RE: What is the best place to locate a clean air intake? low or high on a side of a wall? or on a roof?

If you want to maximize air exchange within a shop more than one intake should be used with most of them as far away from the exhaust as possible. If they are too close to the exhaust the air will come in and go out too quickly without properly venting a shop

if you want to focus on providing clean air for the operator and the operator spends most of their time in one area then the intake(s) should be such that they forms a line between the operator and the exhaust.

 

RE; What should I weld hoods out of and how big are traditional hoods over a gasser? -and how many CFM should i be looking at to draw the bulk of those gasses off?

 I reckon using what you have to hand is a reasonable way to go. one of the most effective hoods I have seen on a forge was made out of kerosene cans.

I used the left over mini corrugated iron cladding I used for the interior of my shop. 

 

RE: Is there anything better than dryer-type ducting at home improvement stores out of which to build a point extraction arm?

Before I had my fume hood I used to vent my shop while stick welding with my $100 wood work dust extractor and 4" PVC storm water ducting. As a point extractor I used a 10 ft length of transparent PVC 4" flexy ducting suspended from a wire between two walls of my shop. The wire and flexy traversed across the top of my small metalwork bench and I could slide the flexy along the wire to get it directly above the work. At first I was very conservative as to how close I would let the end of the flex get to the work but I quickly noticed that (especially at night) the transparency of the flexy enabled me to see how far the sparks would get down the duct but in was never more than a ft at most as the rush of air seemed to cool them down rapidly.Sure the flexy got a few holes and charred marks but it worked well for 6 years and had plenty of life left.  A few times I thought about including a metal chip catcher between the flexy and the dust collector (which was outside my shop) but I never bothered because my dust extractor was so weak (1HP) that a lot of metal dust never would settle out in the flexy so every few months I had to take it down and empty it out. The other thing that the welding fumes did was gum up the extractor bags so they had to be washed more often than I liked which is why I decided to make a fume hood for my new shop.

 

You could use a combo of both the dryer metal type ducting for the first couple of ft and then PVC after that

 

BTW most conventional dust extraction units simply cannot pull more than about 400 cfm through 4" ducting.

6" ducting can carry ~1250 cfm BUT a 3HP or greater motor and 13" or greater diam impeller is also needed.

OTOH using 6" ducting on a small dust extractor will result in the dust settling out in the ducting as happened to me above

 

There is a very instructive chart/graph around on the web that shows what CFM can flow through what diam ducting under what pressure. I have measured the flows through a lot of ducting and blowers and this chart has rarely been wrong. Anyone contemplating setting up a ducting system should really study this to see what is possible and what is not. 

 

 

Very interesting responses. Thanks for the help. Do you know which chart you used. There are so many and most I can't seem to readily understand. Also how many cfm rated motor-fan is best for 6"?

[Frosty]

Hmmm. Putting a hood over a 4'x8' area isn't what I'd call a point extraction system, I'd consider it an area system. I'd use a 8'x12' hood as a departure point but you're going to need a serious exhaust blower to get something that size to draw. It's not like a TIG puts out enough heat to make the smoke/fumes draw by their own energy.

 

You could experiment with construction paper and dryer ducting to determine required CFM and build it from more permanent materials later. A little borax/water solution will make paper construction board, etc. or just paint it, for reasonably fire resistance. Use white to help reflect IR. this is just a test device, keep a fire extinguisher handy and pay attention.

 

From my experience a point system would be a cone or little hood, say 12"dia or maybe 14"x14" suspended on an arm by 4""-6" dia flex ducting. you'd simply swing it over and pull it down over the work with just enough room to see and work the welds. A bathroom exhaust fan would be plenty of CFM draw. Seriously, we used to lay an exhaust duct on the table near where we were welding adjust so it draws the smoke/fumes without effecting the shielding gas plasma column.

 

 Unless there were more than three people welding we'd get plenty of makeup air under doors, if not we'd open a window across the room and this was in an LA county California schools so you betcha it met OSHA and better regs. that was late 60's early 70's standards so adjust for modern regs.

 

Frosty The Lucky.

[Avadon]

Hmmm. Putting a hood over a 4'x8' area isn't what I'd call a point extraction system, I'd consider it an area system. I'd use a 8'x12' hood as a departure point but you're going to need a serious exhaust blower to get something that size to draw. It's not like a TIG puts out enough heat to make the smoke/fumes draw by their own energy.

 

You could experiment with construction paper and dryer ducting to determine required CFM and build it from more permanent materials later. A little borax/water solution will make paper construction board, etc. or just paint it, for reasonably fire resistance. Use white to help reflect IR. this is just a test device, keep a fire extinguisher handy and pay attention.

 

From my experience a point system would be a cone or little hood, say 12"dia or maybe 14"x14" suspended on an arm by 4""-6" dia flex ducting. you'd simply swing it over and pull it down over the work with just enough room to see and work the welds. A bathroom exhaust fan would be plenty of CFM draw. Seriously, we used to lay an exhaust duct on the table near where we were welding adjust so it draws the smoke/fumes without effecting the shielding gas plasma column.

 

 Unless there were more than three people welding we'd get plenty of makeup air under doors, if not we'd open a window across the room and this was in an LA county California schools so you betcha it met OSHA and better regs. that was late 60's early 70's standards so adjust for modern regs.

 

Frosty The Lucky.

 

Yah that's what I was wondering, if I need the small point extraction exhaust and then a large hood the size of the table as well ~4x8. That might just be overkill. Like you said, too much power is required to create a draw on that size. I really like your cardboard hood idea. I think I might try that (higher up of course) over my forge to see if it can help. I guess with that much heat rising up, if you have sufficient intake, it should pull fresh air in at an immensely rapid level.

 

how does one test to make sure they have enough fresh air in a shop when forging? Is a CO detector enough or would I be better off buying something that can tell me how fresh the air is?

[SnailForge]

I was trying to find a good semi-flex hose that didn't cost a million dollars. Do you know of any good semi-rigid hose you can use without having to shell out $1200 for a point extraction arm?

 

The ones they use for hot air tumble dryers and kitchen exhaust? They are fairly cheap.

[Alan Evans]

Much as you don't want change all the air in the building for heat loss reasons if it is all contaminated there is not much else you can do....however if you change the air rapidly the temperature will re-establish itself very fast as the incoming air is heated by the thermal mass of the walls floor and equipment in the room.

To that end positive pressure ventilation is more efficient than extraction. It is how the Fire Brigade clear a building of smoke.

Look it up if you think it may work for your circumstance. I have found it very successful from the point of ventilation and sound suppression...no air born noise carried out with the extraction.

Alan

[Avadon]

Much as you don't want change all the air in the building for heat loss reasons if it is all contaminated there is not much else you can do....however if you change the air rapidly the temperature will re-establish itself very fast as the incoming air is heated by the thermal mass of the walls floor and equipment in the room.

To that end positive pressure ventilation is more efficient than extraction. It is how the Fire Brigade clear a building of smoke.

Look it up if you think it may work for your circumstance. I have found it very successful from the point of ventilation and sound suppression...no air born noise carried out with the extraction.

Alan

 

Can you tell me how positive pressure ventilation works? I couldn't find much on google about it in a shop.

[Alan Evans]

I did not base it on any shop specific information. I just adopted and adapted the principle of the Fire Brigade's system which made sense to me. It has been in successful operation in my forge for twenty odd years. I have a speed controller on the fan so it can just tick over a clear the air fast.

Have a look at the recent IFI thread about straw bale building, I described it on that.

I have just been out and braved the stinging nettles to take a photo or two of the air duct / chimney breast for you.


Alan