Idea for Darkroom Ventilation - input please

horacekenneth · Nov 19, 2015

I need to put some ventilation in my darkroom, something that doesn't fill it with cold air or suck out all the hot air. I read about chemical fumes and how they are heavier than air and you need to ventilate them away from yourself. My idea is to build a metal/wood box shaped like a long darkroom sink in which to put the trays and attach a low power fan to the long far side of the box to suck chemical fumes away and out.

Thoughts? As much as I'd love to put in positive heated pressure I just don't think there's a good place to pump heated air in from my location.

Vaughn · Nov 19, 2015

The main thing to consider is to have fresh air passing by your head on its way to pick up the chemical fumes. I think your way does that, if I have pitched it correctly.

As far as losing heat, the only way around it would be some sort of heat-exchanger between the hot air going out and the clean colder air coming in. $$

As an aside: I use acetone, so I am considering a collaspable fume hood -- some plexiglass sheets that can be quickly put together on my work surface to form an open ended box with a way to tie it in with the exhaust fan. I have done something similar with cardboard and clear plastic garbage bags.

DREW WILEY · Nov 19, 2015

I have an auxiliary portable fume system attached to my main fume hood via flexible ducting and a booster squirrel cage fan. But you have
to be careful with flammable solvent fumes like acetone. Typical fan motors are not spark-proof. You need a special type, and also a grounded type of ducting.

Vaughn · Nov 19, 2015

Good point. I have a darkroom fan -- Photo Star Products out of Conneticut -- does not say spark-proof anywhere! Unfortunately no easy way to push air into the system I am thinking about.

The volume I am dealing with at any one time is 18ml of acetone brushed onto a 14x17 sheet. Once that all evaporates, I brush on another 18ml. Is this a significant amount in regards to fan motor sparks?

Ronald Moravec · Nov 20, 2015

My input is on a wall opposite the exhaust. Construction is drywall over studs. cut a hole register size low on outside and high on inside. Light can not bend around two 90 deg angles five feet apart. Cover with cold air return louvers. Been working for 35 + years.

Wayne · Nov 20, 2015

Why are you so concerned about heated air coming in/going out? Yes there will be some heat loss but its not like the temperature is going to drop 20 degrees so you won't need heated air pumped in to replace it.The intake can be passive, and as long as the air coming in is heated OR you have heat in the darkroom you should be fine. I'd be concerned that your contraption be designed so you can be sure its doing more good than harm. Will it give you cleaner air to breathe than if you just ventilated the whole room properly? My darkroom is in a (normally) unheated room above my garage. I turn the heat on a couple hours before I plan to work in there and except on real cold windy winter nights I can usually shut it off and leave it off once I start working, despite the fan pumping heat outside.

horacekenneth said:
I need to put some ventilation in my darkroom, something that doesn't fill it with cold air or suck out all the hot air. I read about chemical fumes and how they are heavier than air and you need to ventilate them away from yourself. My idea is to build a metal/wood box shaped like a long darkroom sink in which to put the trays and attach a low power fan to the long far side of the box to suck chemical fumes away and out.

Thoughts? As much as I'd love to put in positive heated pressure I just don't think there's a good place to pump heated air in from my location.

mfagan · Nov 20, 2015

I agree with Wayne. I had a small darkroom built into a garage renovation, and the ventilation is the principal thing I didn't get right. The slow-moving air is moist from darkroom work and leads to a musty smell (even though I had bathroom-type drywall installed). I leave the door wide open whenever possible (and accept the dust that results); but it would have been better for me to have a better flow going in there to start with. It is supplied with household HVAC, and I leave that blower as well as a bathroom exhaust fan over the sink turned on 24/7 -- but as I said, that's not sufficient to keep my 70 sqft space supplied with sufficient fresh air.

Neal · Nov 20, 2015

Dear horacekenneth,

A heat recovery ventilator might be something to consider. I'm sure there are less expensive ones than the one in the link.

Good luck,

Neal Wydra

horacekenneth · Nov 20, 2015

Wayne said:
Why are you so concerned about heated air coming in/going out? Yes there will be some heat loss but its not like the temperature is going to drop 20 degrees so you won't need heated air pumped in to replace it.The intake can be passive, and as long as the air coming in is heated OR you have heat in the darkroom you should be fine. I'd be concerned that your contraption be designed so you can be sure its doing more good than harm. Will it give you cleaner air to breathe than if you just ventilated the whole room properly? My darkroom is in a (normally) unheated room above my garage. I turn the heat on a couple hours before I plan to work in there and except on real cold windy winter nights I can usually shut it off and leave it off once I start working, despite the fan pumping heat outside.

The only heat I have access to in my darkroom is a space heater. With my current ventilation system (read: drafty room) it can get too cold in the winter to print with the developer tray sitting right on top of the space heater. Step 1 this Winter is insulate/seal and step 2 is ventilate.

This article about darkroom ventilation (Dead Link Removed) talks about the importance of pulling chemical fumes away directly from the trays which is where I got the box idea and that perhaps it would count as "proper".

Helpful caution about sparks. I don't think I'm doing any work with acetone, any other flammable darkroom chemicals I should be aware of?

Wayne · Nov 20, 2015

I use an aquarium heater in an 11x14 tray to float my 8x10 developer tray in. It provides perfect temperature control every time. I stand the PET bottles of fix and stop in the heated tray for 30-60 minutes to bring them up to temp, but once I pour them into the trays I don't worry about them.

I guess I'd invest in an aquarium heater and better space heater before skimping on ventilation. Your ventilated box might work, but it would have to be designed well. I've considered something like that myself for doing RA-4 in trays, so I'd be interested in seeing well-engineered designs.

horacekenneth · Nov 20, 2015

Wayne said:
I use an aquarium heater in an 11x14 tray to float my 8x10 developer tray in. It provides perfect temperature control every time. I stand the PET bottles of fix and stop in the heated tray for 30-60 minutes to bring them up to temp, but once I pour them into the trays I don't worry about them.

I guess I'd invest in an aquarium heater and better space heater before skimping on ventilation. Your ventilated box might work, but it would have to be designed well. I've considered something like that myself for doing RA-4 in trays, so I'd be interested in seeing well-engineered designs.

Interesting - heated trays. That is a great idea.

Idea for Darkroom Ventilation - input please

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