Sciencemadness Discussion Board - Safe and cheap fumehoods

Safe and cheap fumehoods

nitropyrotech - 25-7-2025 at 18:30

I mainly do nitrolysis or nitrations, sometimes I work with hydrazine but nothing too speical. I always worked with a full face gas mask with ABC protection from the brand Dräger and a Fan, basically in my gardenhouse with the window open and a fan, wich wasnt that great, if I took the mask off I wouldve smelled NOX gases wich is actally not good, thats why I want to buy or build an fume hood, I did some research and came out that, I could buy a pretty good fume hood from china for 800 USD incl shipping. It perfectly fits into my garden house and looks pretty good. I am also planning to do more organic chemistry so I will need one. I really want to avoid building myself an fumehood or buying an expenisve one locally so what do you guys suggest I should do

thoughts ........

Sulaiman - 25-7-2025 at 19:04

A link to the site of the fume cupboard would focus comments.

eg does the price include a flameproof fan etc.

remember, fume hoods/cupboards do not eliminate fumes, they just move them to somewhere else,
the reason fume cupboards are purchased is to increase fume production

neutralising fumes (eg wash bottles, filters) is good

fume cupboards require large volumes of air to be expelled from the building,
to be replaced by lovely fresh air - that may be too hot or too cold for comfort.

Afterthought:
By buying a fume cupboard you will increase the periods between re-decorating and/or replacing corroded objects
so it is easy to financially justify the purchase
and as a bonus you will be safer and more comfortable - happier

[Edited on 26-7-2025 by Sulaiman]

nitropyrotech - 26-7-2025 at 00:48

Quote: Originally posted by Sulaiman

A link to the site of the fume cupboard would focus comments.

eg does the price include a flameproof fan etc.

remember, fume hoods/cupboards do not eliminate fumes, they just move them to somewhere else,
the reason fume cupboards are purchased is to increase fume production

I have a pretty big garden so filtration wouldnt be a problem so I prob dont need a filtration system for most of the things that I do, if it would be in a different thing if I would live in a city but I think I dont need it. I also wanna buy the fume hood that I attach, it is pretty cheap compared to the ones I find used or new locally, and it fits in my garden house wich only has an height of a bit over 2.10m so overall it cost me 888. And yeah these shit NOX corroded, everything out of metal in my garden house

from the compressor, electrical plugs..., but still its a pretty expensive investment, you think a selfmade one with a 4 inch fan will do the same?

Here the fume hood: https://german.alibaba.com/product-detail/Chemistry-Fume-Hoo...

Belowzero - 26-7-2025 at 01:14

Bought a full sized fume hood from an auction for next to nothing.
Getting the thing moved was an interesting challenge. The sliding window with the counter weights are crazy heavy.
And the overall object is huge, even had to saw a hole in the ceiling of my shed to fit it in.
A bigger challenge was the exhaust fan part. Building a fan box, making a hole through the roof and the wiring.

Total costs was around ~400$
Not bad but a lot of work.

Dr.Bob - 27-7-2025 at 08:11

I have sold two hoods from the lab I cleaned up, both went for $100 if you removed them, and two people from a ways away came and got one each. But I see people advertising them often on Craigslist or other places. They are a pain to disassemble and move, but if you look, you can likely find one from a university remodel, business closing, or retired science geek. You can build something that might work with plywood, metal, ducting, and a fan, but it will not be as nice as the ones you can find cheap if you have the time to take them apart and rebuild.

Belowzero - 28-7-2025 at 11:27

Quote: Originally posted by Dr.Bob

I have sold two hoods from the lab I cleaned up, both went for $100 if you removed them, and two people from a ways away came and got one each. But I see people advertising them often on Craigslist or other places. They are a pain to disassemble and move, but if you look, you can likely find one from a university remodel, business closing, or retired science geek. You can build something that might work with plywood, metal, ducting, and a fan, but it will not be as nice as the ones you can find cheap if you have the time to take them apart and rebuild.

Yes absolutely.
Buying one is quite likely cheaper too.

I took a full sized hood apart and it took me a long time to figure out how to put it back together again. 2 moving windows with counter weights and a half dozen steel cables and pulleys. Really impressed by the level of engineering going into this.
Getting the top lifted back on required a chain pulley block attached to the ceiling.

That should go as a warning too, know what you are getting into OP.

[Edited on 28-7-2025 by Belowzero]

bariumbromate - 28-7-2025 at 20:21

made this one only costed $100USD https://www.youtube.com/watch?v=bi4yCLBmvlg

MrDoctor - 29-7-2025 at 01:41

from experience i can tell you, its really important to have some air guides in the hood to stop air from tumbling around in the corners. SM library has a document somewhere explaining this but essentially a sheet suspended over the air intake forcing air to be drawn from the bottom back corner and the top front corner of the ceiling, results in less opportunity for vapor to accumilate and leak/escape. the fact that you can throw some smoke into the hood and it will cycle around for a good few seconds if not more, before leaving, if you just have a hole in the top for the fan and call it a day, is surprising and disturbing.

I built mine however by taking one of those cheap work benches made from universal shelving kits, and enclosing it in sheet metal, and going from there. it works, but it could do with some improvements. recently i wound up exposing myself to some nasty solvents because i still havent added an aerofoil on the bottom edge where air flows in. its not too bad but a smoke bomb test also shows air tumbles about in a horizontal cylindrical vortex which is able to kind of fling stuff out. but its been easier yet to just not put things on the edge of the fumehood, a good fumehood shouldnt leak from there but its still kind of asking for it imo expecting protection when its barely inside.
Make sure you have nice laminar flow if you DIY one, and again, the SM library has a few docs on what some of the bare minimum requirements are, a hole in the top of a box is insufficient even if you can slide the window up and down almost shut.

some more thoughts from someone who does not (yet) have a fume cupboard

Sulaiman - 29-7-2025 at 19:16

If practicable, install the fan at the exit end of the air duct,
Because if the extractor fan is at the fume cupboard end of the air duct
then the air duct will be at a positive pressure relative to the atmosphere
so any leak/crack/tear in the duct will allow the fumes to enter the lab.

Having the fan at the exit end of the air duct would be quieter as it will be farther away,
and can have some noise absorbing stuff around it.

I would like a big red button that I can press at any time to switch the exhaust fan to max turbo/panic mode.

.Check that the negative pressure due to the fan at full speed cannot collapse the air duct before starting your installation.

try to not have a U-bend in the air duct - that could accumulate stuff

MrDoctor - 30-7-2025 at 01:23

yes, this ^
you would be surprised, how just out of nowhere rats and roaches will look at some PVC ducting and think, hell yeah, im gonna eat that!!
Also in the event you scruff or nick the ducting, some ductape is all it takes to reliably fix it on the negative side, wheras positive, it also may but youll never really know if its leaking until one day its bad enough you can smell it.

Bounce house inflators make great fans for this, depending on the scale, because they are nice and cheap and the output is well pressurized so you can send it up a chimney of some sort relatively easily, releasing fumes up in the air where they are less likely to bother anyone, or blow back into your house or windows, and some simple PVC gutter pipe (cheap low pressure kind) will do the trick, needing only being no wider in diameter than the outlet of the fan. They are loud though, but cheap, would probably be good as a second fan on the outlet for that turbo panic mode.

teodor - 30-7-2025 at 03:56

I use glass fiber fabric to shape the air flow inside a fume hood. Without that there is no air flow on the bottom going to the back which is necessary for working with fumes which are havier than air. You can easily adjust the air flow using the fabric and the air flow meter. Also the fabric is sucking fumes from the whole area. I cover back and top with the fabric leaving the narrow opening in the bottom and making some area between the back wall and the fabric and much bigger between the top and the fabric. The fabric can protect the sides from the hot air (e.g. from a heat gun or gas burners) and the top area is needed to cool the air before sucking it into an air pipe. The fabric from glass fiber withstands 600C. I use aluminium as a construction material also for pipes. It has quite good resistance despite some little corrosion but there were no issues with this material. There is some choise for the glass. You can use the armored one (a sandwitch consisting of interlaced layers of glass and polymer) for better protection but it will require some counterweight for the sash window because it will be quite heavy to lift it by hands. Consider it if you can expect explosions otherwise don't use any heavy glass. I used polystyrene in the first hood version.
And start with buying an air flow meter. The measurement is the key of the succesfull fume hood setup.

[Edited on 30-7-2025 by teodor]

[Edited on 30-7-2025 by teodor]

Belowzero - 30-7-2025 at 09:46

Quote: Originally posted by Sulaiman

I would like a big red button that I can press at any time to switch the exhaust fan to max turbo/panic mode.

Good idea!
I still need to properly do the wiring and will certainly include this feature!
I am using a triac to control the fan speed and that could easily be bypassed with such a panic button.
Thanks.

nitropyrotech - 2-8-2025 at 06:44

Quote: Originally posted by Belowzero

Bought a full sized fume hood from an auction for next to nothing.
Getting the thing moved was an interesting challenge. The sliding window with the counter weights are crazy heavy.
And the overall object is huge, even had to saw a hole in the ceiling of my shed to fit it in.
A bigger challenge was the exhaust fan part. Building a fan box, making a hole through the roof and the wiring.

Total costs was around ~400$
Not bad but a lot of work.

I live in germany and you dont have any type of that auction here, its very rare, not like in the USA, and I only have a 2,4m cealing, so it isnt ideal

Sulaiman - 3-8-2025 at 02:44

Due to the loss of relatively cheap Russian energy
many chemical companies in Germany are closing,
you should be able to buy loads of cheap stuff,
maybe even a small (licensed, registered) chemical business ?

Mateo_swe - 15-8-2025 at 11:40

Build one yourself.
Just get a explosion proof fan and some ducting and make a enclosure.
I use a ordinary EC-fan for ventilation that isnt explosion proof and is hoping the high airflow will dilute any explosion fumes below explosion levels.
Like when working with diethyl ether.
But im careful with this type of explosion prone compounds.
But for toxic stuff its great.
A commercial fume hood is obviously better but a DIY one goes a long way and is much, much better than nothing.