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Author: Subject: Fume Hood Construction
CouchHatter
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[*] posted on 27-6-2019 at 17:45


Here is my completed fume hood. I finally installed the stack on the roof and it is functional! I am done painting for a while, something like 10-15 sessions to get all the parts covered. Ugh.

Sometime I'll make a thread to showcase all the bells and whistles and its construction.

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[*] posted on 28-6-2019 at 03:18


@CouchHatter pretty cool, and big! but what about that horizontal sash? never seen a fumehood using this type of design, is it effective?




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[*] posted on 6-7-2019 at 14:44


Nice hood, but strange sash design.

Anyways, I am working on my own hood right now and would like to know what y’all would suggest I do for baffle dimensions. My hood is 30 inches wide, 28 tall and 18 inches from the front of the actual opening to the very back. Sorry for using inches, I would have preferred not too.
I am using a 500cfm fan.

I’m not sure how much it matters with such a strong fan but it would be nice to have them anyways.



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CouchHatter
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[*] posted on 7-7-2019 at 17:39


It's 5' x 5' x 2'. No one ever said "I wish I made it smaller!":D I haven't seen a horizontal sash in use either, but it was addressed in Laboratory Fume Hoods: A User's Manual. I already owned the tempered window panes and simply cut another frame I had to size. So even if it goes in the bin I'm not out much... I can work around the large panes without sticking my head in, but qualitative testing will determine if it gets replaced with a more conventional solution, or not.

That was only one of the resources I used to design my hood. It was written in 1993 and I didn't really cross-check the horizontal sash thing with other books, so I will surely test it before using it much. Water is pulled 3/8" through a 3/16" ID tubing though, and the face velocity seems to be excellent. It completely removed the smoke from a tiny smoke bomb ~8 inches outside the hood. Now that firework season is over, I have a supply of bigger smoke bombs to really put it to the test. Just need some extra time.

Abromination, how wide is your duct? Look at page 21-22. The only dimension I would change would be the middle Slot B, to make it more close to the bottom third of the hood.

back baffle design p16-23

sash varieties p22-27


I made the pages barely too big so I'm just linking them in lieu of the 8MB attachment limit here.
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Abromination
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[*] posted on 8-7-2019 at 12:57


Quote: Originally posted by CouchHatter  
It's 5' x 5' x 2'. No one ever said "I wish I made it smaller!":D I haven't seen a horizontal sash in use either, but it was addressed in Laboratory Fume Hoods: A User's Manual. I already owned the tempered window panes and simply cut another frame I had to size. So even if it goes in the bin I'm not out much... I can work around the large panes without sticking my head in, but qualitative testing will determine if it gets replaced with a more conventional solution, or not.

That was only one of the resources I used to design my hood. It was written in 1993 and I didn't really cross-check the horizontal sash thing with other books, so I will surely test it before using it much. Water is pulled 3/8" through a 3/16" ID tubing though, and the face velocity seems to be excellent. It completely removed the smoke from a tiny smoke bomb ~8 inches outside the hood. Now that firework season is over, I have a supply of bigger smoke bombs to really put it to the test. Just need some extra time.

Abromination, how wide is your duct? Look at page 21-22. The only dimension I would change would be the middle Slot B, to make it more close to the bottom third of the hood.

back baffle design p16-23

sash varieties p22-27


I made the pages barely too big so I'm just linking them in lieu of the 8MB attachment limit here.


Here are the two real blower options I am looking at:
https://www.amazon.com/Fasco-A455-Centrifugal-Blower-Bearing...

https://www.amazon.com/gp/aw/d/B01MTFZSP5/ref=cm_cr_arp_mb_b...

I probably wont get the seaflow one, and the first fasco one doesn’t give me the input or output diameters.


The information on the baffles was super useful, that will be the next step after I install the sash.
Thank you, mate




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[*] posted on 19-7-2019 at 09:55


The first baffle and lighting has been installed and I have decided on what blower I want. I know that in professional labs that the blower is connected directly to the outside plenum, but is this better then installing it directly onto the hood body?

I put some regularly used equipment in to get a better feeling about space inside of the hood.

Next project is the sash and the control panel.

86597E17-CA31-4840-87F9-EAFC755C0748.jpeg - 2.2MB




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[*] posted on 20-7-2019 at 09:16


Looking good Abromination! Though I fear for that sep funnel's life, never seen one held that way:P

There is a chapter about duct work... I think ear comfort, multiple hoods, and vibration are why it's done that way professionally. The most important reason I can think of, though, is so that there's no positive pressure in your duct.

Having the blower directly after the hood means that any tiny hole or crevice in the duct after the blower will push air into the room and not be exhausted.

Having the blower as close as possible to the end of the duct means that everywhere before the blower is under suction, and that even if there are small gaps in your duct, it will only imperceptibly lessen your air velocity.

As long as you're certain that everything after the blower is airtight, and are certain the dB levels won't be an issue for constant use, and don't set loose things in the hood that might vibrate around, I'd say it's an option.

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[*] posted on 20-7-2019 at 13:54


Quote: Originally posted by CouchHatter  
Looking good Abromination! Though I fear for that sep funnel's life, never seen one held that way:P

There is a chapter about duct work... I think ear comfort, multiple hoods, and vibration are why it's done that way professionally. The most important reason I can think of, though, is so that there's no positive pressure in your duct.

Having the blower directly after the hood means that any tiny hole or crevice in the duct after the blower will push air into the room and not be exhausted.

Having the blower as close as possible to the end of the duct means that everywhere before the blower is under suction, and that even if there are small gaps in your duct, it will only imperceptibly lessen your air velocity.

As long as you're certain that everything after the blower is airtight, and are certain the dB levels won't be an issue for constant use, and don't set loose things in the hood that might vibrate around, I'd say it's an option.



Don’t worry, it’s quite stable and easier to manipulate with the clamps I have, there is a wide joint at the bottom :)
I will be putting the blower on the end of the duct, which will also help with noise. Thanks again for your help!




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[*] posted on 23-11-2019 at 10:51


Since one of my skills is 3d modeling , I decided to 3D model a fume hood and make a set of prints to go along with it.
been working on this with no sleep , abound 12hrs or so.

I'm still working on getting the rest of the prints made for all the pieces but for now that's what I have
Might design a cabinet to go underneath it later

Fumehood_2019-Nov-23_02-51-36PM-000_CustomizedView10416511436.jpg - 39kB

Fumehood_2019-Nov-23_03-18-19PM-000_CustomizedView24340908386.jpg - 45kB

Fumehood_2019-Nov-23_09-40-12AM-000_CustomizedView24959278170.jpg - 64kB

Fumehood_2019-Nov-23_09-41-29AM-000_CustomizedView5030036424.jpg - 53kB

Fumehood_2019-Nov-23_12-06-07PM-000_CustomizedView17738241554.jpg - 54kB

Attachment: Fume Hood project.pdf (176kB)
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[*] posted on 2-2-2020 at 04:51


Quote: Originally posted by CouchHatter  
Sometime I'll make a thread to showcase all the bells and whistles and its construction.


Here are my post-process notes on my fume hood building.
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Abromination
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[*] posted on 9-2-2020 at 15:23


After 6 months of work, my fume hood is complete!
I am very happy with the face velocity at the sash and the lack of turbidity in the body itself. It has two settings, one being 500 cfm and the other around 350. It also houses controls for lighting, vacuum and power. It is capable of pulling a tissue from the sash opening to the fan (oops) and hot, concentrated acetic acid is not detectible even when set a few inches away from the sash outside of the hood. A smoke bomb ignited within the hood was easily taken care of with the low setting.
The main box is 24x18x30 inches, with baffles sitting in the back (thanks for the help with those, CouchHatter, they work great)
Only problem is it is not useable in the winter. It pulls air from the chimney on the other side of the house (cold) and through the gaps in the outlet window (fixable by cracking the door)
I will post pictures in a few.

[Edited on 2-9-20 by Abromination]

1A49188B-EFF4-4291-8B31-1B49891F7B0B.jpeg - 1.8MBA9977FD0-360C-4C67-B6C7-F41621C164D1.jpeg - 2.2MB




List of materials made by ScienceMadness.org users:
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[*] posted on 9-2-2020 at 15:45




[Edited on 2-9-20 by Abromination]

3A5DD71F-295C-40A4-9491-DDB13D4A4BED.jpeg - 2.3MB3BDA01E2-C262-43F6-8771-F1E641DE69C4.jpeg - 1.9MBE5FADA12-E5AA-4D72-BC88-B7C35FC0CC1F.jpeg - 1.9MB




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[*] posted on 24-5-2020 at 08:50


Where do you guys evacuate the fumes?

When I made cyanides years ago, I did it outside and I made a temporary fume hood out of planks and plastic membrane, and I just put up a duct fan on top of it, and a 3-meter long pvc tube to blast any fumes up to the sky.
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[*] posted on 24-5-2020 at 13:44


Just outside, I have an outlet at 2.5 m above ground. But I don't do any large scale and very toxic things so it should be quite safe.

One day I made few moles of nitrogen dioxide and it was a bit noticeable outside. Now I try to scrub as much nasty stuff as I can and I fill much better because I don't know why by I don't trust the tubing and vent which sits right on the hood and instead of sucking it pushed air to outside.

@Abromination: you could make it a bit taller - my hood has similar height and sometimes it is hard to fit required apparatus :( Heating mantle, distillation head and thermometer take almost everything. I have 40cm vigreux which is currently unusable.

I am thinking about finishing the larger hood, but if I get it my wife will kill me - I would go home only for sleep :D
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[*] posted on 25-5-2020 at 00:21


I think that maube a good addition to the fume cupboards shown above would be some kind of spill containment,
maybe a one inch tall pice of wood across the front of the hood floor to act as a dam/barrier.




CAUTION : Hobby Chemist, not Professional or even Amateur
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[*] posted on 29-8-2020 at 09:55


Finally got the beginnings of a fume hood!

Going to take a bit of work to set it up at the shop, first problem is it did not come with a blower.... Thinking of getting an 8" duct fan like this:

https://www.amazon.com/VIVOSUN-Inline-Variable-Controller-Ve...

The opening on top of the fume hood is 12", thinking of stepping that down to 8" for the blower, then down to 4" and a Y-valve into the bathroom fan duct and out the roof. I'll send more photos of the setup as the project progresses.... Hoping that the 4" diameter on the exhaust is not too restrictive, and also concerned about fluids condensing inside the ducts and dripping down, yuk. But it's a start...

Other things I'd like to add is a distillation rack inside the hood, and either some cabinets below, or some other way of elegantly mounting a vacuum pump and a recirculating chiller... A variac for adjustable AC, maybe a temperature PID controller, and more valves/plumbing for things like chilled fluid would be cool...

EDIT: on second thought, I have two exhaust options, see second photo. Circled in red is the 5" copper sewer drain vent, and in blue is the 4" galvanized steel vent from the bathroom "fart fan". I was planning on tying into the 4" galvanized steel duct, as it's much cheaper and easier to work with. Also to replace when it corrodes....

Tying into the 5" copper vent is tempting, but looks harder and more expensive to work with, and I'd hate to hate to replace it all two years later... Hmmm.... tough decision....

FumeHood2.jpg - 478kB


EditedFumeHoodExhaust.jpg - 1.8MB

[Edited on 8-29-2020 by 1KEE]
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[*] posted on 29-8-2020 at 14:41


Your hood looks solid, Abromination. I missed your followup posts. Glad I could give you some good info! The grill on top is a nice touch. Is it from an audio receiver? And what is the hose hookup inside your hood being used for?
Makeup air is definitely an institutional luxury. I've just resigned to freezing in the winter:D

1KEE, that is a really nice one! I can't personally speak to using that small of ducting, but I think that as long as your blower is configured correctly then you might be able to get away with it. Although it will definitely limit your exhaust per minute, even with a larger blower. Not a big problem as long as you learn good sash etiquette.
As for corrosion, I think that most (myself included) underestimate the duct and fan parts ability to withstand fumes. Unless you are making an extreme amount of corrosive gasses and don't scrub them, the metal ducts ought to last longer than 2 years. I took my hood blower apart after a year of use and the metal parts were barely touched. I am unsure how copper stacks up against galvanized steel, though.
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[*] posted on 29-8-2020 at 15:19


I started working last year with the idea of building a fume hood.
So far I drilled a hole in the wall (30cm concrete wall, not fun) and passed a tube through. Outside I put a box with two activated charcoal filters, one for acid vapors and one for solvent, and an atex rated three phase blower connected to a VFD to control the speed.

On the inside however, it's still quite lacking, as basically the real fume hood just isn't there, for now there's just the tube.

fumehood.jpg - 154kB

Do you think a fully enclosed fume hood would be much better than my current set up? I'm currently unsure whether it makes sense to finish the job or leave it as is.
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[*] posted on 29-8-2020 at 17:28


How many CFM or RPM is your exhaust blower? My blower manages to cause a draft from the lab below even without the connecting ductwork in place. But a smaller fan won't really catch enough ambient fumes to mention, unless you stick a tube from the vacuum outlet directly in the dryer vent. Room pressure might also play a large part in your case. Some schools and professional labs have point-of-use exhausts, but I don't know anything about those.
I would put a smoke bomb or titanium tetrachloride etc, even some finely divided powder, directly under your distillation setup and see how easily your duct captures the fumes.
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[*] posted on 29-8-2020 at 21:24


Quote: Originally posted by beta4  
I started working last year with the idea of building a fume hood.
So far I drilled a hole in the wall (30cm concrete wall, not fun) and passed a tube through. Outside I put a box with two activated charcoal filters, one for acid vapors and one for solvent, and an atex rated three phase blower connected to a VFD to control the speed.

On the inside however, it's still quite lacking, as basically the real fume hood just isn't there, for now there's just the tube.



Do you think a fully enclosed fume hood would be much better than my current set up? I'm currently unsure whether it makes sense to finish the job or leave it as is.


Nice. I actually used a fume exhaust tube for a while. They work pretty well for a lot of things, but they aren't so great for containing runaway reactions and accidents. Eventually, you'll want a cabinet and sash, as well as some means for containing spills.
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[*] posted on 30-8-2020 at 01:01


Quote: Originally posted by CouchHatter  
How many CFM or RPM is your exhaust blower? My blower manages to cause a draft from the lab below even without the connecting ductwork in place. But a smaller fan won't really catch enough ambient fumes to mention, unless you stick a tube from the vacuum outlet directly in the dryer vent. Room pressure might also play a large part in your case. Some schools and professional labs have point-of-use exhausts, but I don't know anything about those.
I would put a smoke bomb or titanium tetrachloride etc, even some finely divided powder, directly under your distillation setup and see how easily your duct captures the fumes.


The blower is a 180W unit, 2750RPM. It is supposed to do 590CFM at the maximum speed, but the actual number in my setup is quite lower due to the airflow resistance caused by the filters. I don't know how to measure it.

I didn't try to make a lot of smoke to check how well it works, but that's a good idea.
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[*] posted on 30-8-2020 at 03:06


Using this tube and blower you can make disposable hood by attaching thick foil and covering working area. Not as good as standard hood but better than just the tube when you're afraid that something may get out of control
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[*] posted on 30-8-2020 at 14:23


Hello, i’ve just worked out what CFM I need and it’s 725CFM or 1231.78 cubic metres/hour.
I’ve also got to use a couple of bends to manipulate where i’m mounting the fan. I’ve there decided to purchase a fan locally (UK) which is corrosive resistant, made of polypropylene, and rated at 2100m3/hr. I will then need to purchase a triac speed controller.
I see some systems use a manual or automatic duct damper straight after the exit of the fume cabinet. Are any of you using a duct damper?
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[*] posted on 30-8-2020 at 14:59


Quote: Originally posted by CouchHatter  
Your hood looks solid, Abromination. I missed your followup posts. Glad I could give you some good info! The grill on top is a nice touch. Is it from an audio receiver? And what is the hose hookup inside your hood being used for?
Makeup air is definitely an institutional luxury. I've just resigned to freezing in the winter:D

1KEE, that is a really nice one! I can't personally speak to using that small of ducting, but I think that as long as your blower is configured correctly then you might be able to get away with it. Although it will definitely limit your exhaust per minute, even with a larger blower. Not a big problem as long as you learn good sash etiquette.
As for corrosion, I think that most (myself included) underestimate the duct and fan parts ability to withstand fumes. Unless you are making an extreme amount of corrosive gasses and don't scrub them, the metal ducts ought to last longer than 2 years. I took my hood blower apart after a year of use and the metal parts were barely touched. I am unsure how copper stacks up against galvanized steel, though.


Thanks! Yes the grill is from an audio receiver, it doesn’t do much more then cover the blower. The hose port on the inside leads to my vacuum pump. Ive made a few improvements since my last post, but for the most part it works perfectly.




List of materials made by ScienceMadness.org users:
https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
--------------------------------
Elements Collected: H, Li, B, C, N, O, Mg, Al, Si, P, S, Fe, Ni, Cu, Zn, Ag, I, Au, Pb, Bi, Am
Last Acquired: B
Next: Na
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