Question on DIY darkroom ventilation

[gdi]

I was using a Nova tent in my unfinished basement darkroom for my printing trays and have set up a 6” duct fan to blow into the large bottom hole in the tent,inflating it, and then exiting at the top of the tent. I have routed that to a basement window with a dryer vent flap installed. There are a couple of problems with this - 1- it blows air from the floor up to the ceiling to extract fumes, right by my face, and 2- it is a PITA to go from the enlarger station outside to the tent and back.

So, I am currently using printing trays on a table in the open outside the tent. I light proofed my entire basement and the area is pretty large - so it isn’t a tight space. But I likely going to set up some form of fume extraction system and the most obvious approach to me is a 4“ diameter PVC pipe with holes drills in one side to run the length of the table a few inches above the trays connected to some flexible hose (6”) or more rigid 4” PVC pipe and adapting and inserted the duct fan in-line. And I would of course vent this out the window.

I have found some materials that my make this easier (though costlier!) but I want to see if anyone has any experience with it . It is Powertec dust collection hoses and pipe- it all comes in 6” and has couplers, pipe and hose. Does anyone have any experience with this type of dust collection system? I can’t see why it wouldn’t work to pull fumes as easily as dust. Also I am trying to decide if I should use 6” or 4” as the initial exhaust section over the trays, and then expand those to 6”. It seems having a smaller diameter initially may increase the air flow and draw the fumes from the trays into the system more efficiently than a larger diameter - but I’m not sure if it will make a huge difference - again, any experience or views on these ideas?

Many thanks!

[Larry Gebhardt]

I think a vent fan the draws air from above the trays would be adequate. I use a vent fan connected to a 4” perforated drain pipe place at the back my sink. It seems to work fine. I’m not that worried about the chemicals I use in the darkroom, but I like that it gets enough fumes that I don’t smell them.

A 600cfm wood working dust extractor seems to me to be overkill. I’d build a fume hood before I went with that.

[Maris Rusis]

Fume extraction is a vexed thing so for my last and best darkroom I eliminated it entirely.
Because I do only black and white work I can use odourless developer, odourless stop bath, and odourless fixer. The no-smell stop bath and fixer cost a little more but with no fumes to extract a fume extractor ($$$) is not needed.
By far the worst smell is acetic acid stop-bath but there is no reason to use it. The citric acid based alternatives work well and don't pong.

[Tin Can]

Fume extraction is a vexed thing so for my last and best darkroom I eliminated it entirely.
Ditto

Because I do only black and white work I can use odourless developer, odourless stop bath, and odourless fixer. The no-smell stop bath and fixer cost a little more but with no fumes to extract a fume extractor ($$$) is not needed.
By far the worst smell is acetic acid stop-bath but there is no reason to use it. The citric acid based alternatives work well and don't pong.

[gdi]

I think a vent fan the draws air from above the trays would be adequate. I use a vent fan connected to a 4” perforated drain pipe place at the back my sink. It seems to work fine. I’m not that worried about the chemicals I use in the darkroom, but I like that it gets enough fumes that I don’t smell them.

A 600cfm wood working dust extractor seems to me to be overkill. I’d build a fume hood before I went with that.

I agree, I was not planning to use a big dust extractor - just utilizing the pipe/hose components. I think your approach is what I’m aiming for and I’m glad it works well!

Thanks!

[gdi]

Fume extraction is a vexed thing so for my last and best darkroom I eliminated it entirely.
Because I do only black and white work I can use odourless developer, odourless stop bath, and odourless fixer. The no-smell stop bath and fixer cost a little more but with no fumes to extract a fume extractor ($$$) is not needed.
By far the worst smell is acetic acid stop-bath but there is no reason to use it. The citric acid based alternatives work well and don't pong.

I process mostly (95%) B&W, but will do some color film processing on occasion (no printing) and I can mix my chemical under the fan as well prior to developing in a Jobo.

Thanks

[Tin Can]

While I don't run a power vent

In winter a big humidifier is under the darkroom sink 24/7

The MERV 16 HVAC filter pulls closeby

in addition this is a leaky old house and that is how I like it

I would not raise a baby in it

[Doremus Scudder]

Keep in mind that if you have a length of pipe with holes drilled in it and are drawing the air from one end, the far end will have much less air flow than the one near the extraction end. You can compensate for this somewhat by making smaller holes spaced farther apart on the extraction end transitioning gradually to larger, more closely-spaced holes at the far end.

If you're planning on a 4-inch pipe, you'll likely find that you need a fan with a fairly large capacity to move enough air to give you adequate ventilation. My darkroom has a 3-inch pipe running the length of the sink under a shelf over the back of the sink. It's just about 4 feet long. The holes at the far end definitely pull less air that the exhaust end, but that's at a place where I only have developer trays. The more-efficient end is positioned over stop and fixer trays.

Best,

Doremus

[domaz]

I have an inline duct fan that vents air outside (exiting via a standard dryer vent) and ducting that runs to the darkroom. In the darkroom I have a piece of flexible hose that sits above my stinkiest tray (the fixer usually) and pulls air from it. It seems to work well, occasionally I do soldering of small electronics and the solder smoke will get pulled right into the duct and not linger in the darkroom. It seems sufficient for a darkroom of "standard toxicity".

[gdi]

I hadn’t thought of progressive holes along the pipe - I’ll keep that in mind!

[gdi]

Since I am not an HVAC engineer, as I assume most of you are ;), I would appreciate any feedback on the feasibility of the following simple solution. I’m thinking of connecting a 6" duct fan in-line in 3" PVC using reducers. I had hoped to find thin walled Schedule 20 or 10, but may have to use schedule 40.

Does anyone have concerns with using the 6" fan (to get more theoretical cfm)? I know the 90 degree elbows with result in drag - but I may test to see just how much.

Thx 234816

[John Kasaian]

I've always figured out the cubic feet of my proposed darkroom first, then went from there
The advantage of converting an existing bathroom is that an adequate vent fan is usually already in situ.

[gdi]

My darkroom is an open unfinished basement, complete with all the associated air leaks, so I would need a huge fan to turn over all the air an adequate number of times per hour. So I’m just planning to position ventilation directly over the source of the most offensive chemical fumes - my development trays.

Thanks

[MILC Toast]

I'm not an HVAC engineer but I don't think I've ever heard of a situation where smaller pipe didn't reduce airflow.

Rather than some inline duct booster fan, I would probably try to find a cheap or used kitchen vent hood which would have CFM ratings and install guides to make sure you get all of that rated CFM. It might have nice lights too.

[gdi]

I'm not an HVAC engineer but I don't think I've ever heard of a situation where smaller pipe didn't reduce airflow.

Rather than some inline duct booster fan, I would probably try to find a cheap or used kitchen vent hood which would have CFM ratings and install guides to make sure you get all of that rated CFM. It might have nice lights too.

Thanks - that what I was concerned about, I may buy a bit of pipe and do a test today and see what happens. I may then check out a kitchen hood.

[John Layton]

...or you could try something like this - with inexpensive six inch flexible dryer vent. In my case, I also utilized a couple of furnace air vents (cut into the sink shelf) and pipes...as well as a couple of internal "shut-off" vanes (not sure what to call them...but like an air valve in a carburetor) so I can control the airflow to each run:
234818

At any rate...what you can't see is the fan above the top of the image - which looks in profile much like the one in your drawing. Funny thing that once I started researching fans online and came up with this one...I started getting lots of online attention from various companies who supply ventilation systems for pot growers!

[domaz]

My darkroom is an open unfinished basement, complete with all the associated air leaks, so I would need a huge fan to turn over all the air an adequate number of times per hour. So I’m just planning to position ventilation directly over the source of the most offensive chemical fumes - my development trays.

Thanks

One idea might be to frame out a smaller room in your basement. My darkroom was in an open basement as well and trying to manage all the light leaks was always a bit much and the dust was terrible. It's a bit of a project but I'm glad I spent the time to frame out a smaller room. Having a dedicated space that you can darken by closing a door, while leaving the rest of the basement alone is great. Also the dust is about 10 times better in the smaller room than the rest of the basement.

[Dugan]

...internal "shut-off" vanes (not sure what to call them...but like an air valve in a carburetor)

"Dampers".:)

[gdi]

...or you could try something like this - with inexpensive six inch flexible dryer vent. In my case, I also utilized a couple of furnace air vents (cut into the sink shelf) and pipes...as well as a couple of internal "shut-off" vanes (not sure what to call them...but like an air valve in a carburetor) so I can control the airflow to each run:
234818

At any rate...what you can't see is the fan above the top of the image - which looks in profile much like the one in your drawing. Funny thing that once I started researching fans online and came up with this one...I started getting lots of online attention from various companies who supply ventilation systems for pot growers!


Excellent - that looks great. I was thinking that flexible duct would drag the air flow but it like you engineered a nice solution. I went to Home Depot today and saw the options are pretty sparse for my design. I may rethink and consider something like you have done. It looks like your ducking is 6”, is that correct?

And, yes the fan I have been using for May Nova tent is one designed for GrowTents !

[gdi]

I was trying to avoid building out a separate room due to the complications. Given the open floor joists I think I would need a ceiling in it to make it fairly air tight so a ventilation fan can do its job. I have gone to the effort of light sealing the large space and it seems to work fine ( and I have learned that distant small light sources are not really a problem.

I guess this big space also reduces the importance of complex venting. Right now I am not standing directly over the trays and the smells don’t bother me at all. I’m just worried that longer term it might be a problem, but limiting my printing to B&W probably means I may be excessively cautious.
With that said - I did consider a quick way to wall off a room and haven’t totally abandoned it - it is called tge “Ever Block” system.

https://www.everblocksystems.com/our-products/?utm_term=ever%20blocks&utm_campaign=&utm_source=google&utm_medium=cpc&hsa_acc=9918802808&hsa_cam=361093476&hsa_grp=25018059636&hsa_ad=509398596676&hsa_src=g&hsa_tgt=kwd-260278926468&hsa_kw=ever%20blocks&hsa_mt=p&hsa_net=adwords&hsa_ver=3&gclid=Cj0KCQiAt66eBhCnARIsAKf3ZNFdAniCCFebjZTASipYHoZZseHjZzeVpkpHfmGPgn9cUUer7t5wgVcaAiuIEALw_wcB

[MILC Toast]

I don't know where you are but in the USA, I would just wait for election day and recycle political signs to make darkroom walls. Get some cheap rough cut 1x4" lumber to make your frame, a handful of screws, a staple gun and tape to put it together and make it light tight. Then a door or curtain of some type. Plumb your ventilation on the exterior and you'll have easy to clean interior surfaces that don't collect dust.

[domaz]

I was trying to avoid building out a separate room due to the complications. Given the open floor joists I think I would need a ceiling in it to make it fairly air tight so a ventilation fan can do its job. I have gone to the effort of light sealing the large space and it seems to work fine ( and I have learned that distant small light sources are not really a problem.

I guess this big space also reduces the importance of complex venting. Right now I am not standing directly over the trays and the smells don’t bother me at all. I’m just worried that longer term it might be a problem, but limiting my printing to B&W probably means I may be excessively cautious.
With that said - I did consider a quick way to wall off a room and haven’t totally abandoned it - it is called tge “Ever Block” system.

https://www.everblocksystems.com/our-products/?utm_term=ever%20blocks&utm_campaign=&utm_source=google&utm_medium=cpc&hsa_acc=9918802808&hsa_cam=361093476&hsa_grp=25018059636&hsa_ad=509398596676&hsa_src=g&hsa_tgt=kwd-260278926468&hsa_kw=ever%20blocks&hsa_mt=p&hsa_net=adwords&hsa_ver=3&gclid=Cj0KCQiAt66eBhCnARIsAKf3ZNFdAniCCFebjZTASipYHoZZseHjZzeVpkpHfmGPgn9cUUer7t5wgVcaAiuIEALw_wcB

I solved the open floor joist problem in my darkroom by cutting small sheets of drywall to fit between each joist. They will never exactly fit so I then filled the gaps with expanding foam which I cut flush with the drywall once it sets. Just using a sheet of drywall for a ceiling is of course the proper way- but that would have been extremely difficult in my old house where the joists do not sit evenly and are all of a slightly different size.