Darkroom Ventilation advice, please

[David Wolf]

I’d appreciate some help, please, to clarify a couple things about properly ventilating a darkroom. Thanks in advance to all ~

The space:

11’ x 13’ ground floor room opening onto 5’ x 7’ alcove. The doorway from outside is along the 11’ wall, which has an adjacent eye-level, sliding window, 14” x 34”. (Because of the sliding action, the actual window opening is about 15” wide.)
The alcove, where the darkroom will be, opens into the opposite corner away from the front wall. There’s a second, sliding window at eye-level here that’s approx 22” square (8” wide opening). The sink will face this window.

So, I’m thinking to put a Doran 400 CFM fan in the window in the larger room to draw fresh air in, and a passive air outlet through a light louver in the window above the sink in the alcove to release the fumes outside while maintaining a positive pressure. (I've been told positive air pressure is important to reduce the amount of dust in the darkroom.)

Or should it be the other way around? with the passive, louvered inlet of fresh air flowing into the larger room and the fan serving to exhaust (extract) the fumes above the sink and out the alcove window?

Which is correct?

I think what’s confusing me is the idea of positive pressure necessarily being created by a stronger in-flow of air relative to the fumes leaving the space.

Also appreciated would be tips on how to keep the fan area facing the outside dry, as well as alternates to the Doran fan and louvers as needed. And is some type of additional air filter on the intake side needed as well?

Many thanks for your kind advice and shared experience!

[Vaughn]

I have heard told and seems to be true, that fans have an easier time pulling air out of places than fans trying to push air into places (air being able to compress, etc). You will want to have the air pulled over your trays and away from your face, then exhausted. The passive exhaust system via positive air pressure as you describe might work in a nicely balanced system, but would be interrupted by any significant air movement caused by you moving and the opening of doors, etc. If you can make a box for the exhaust fan that can hang in the window, or sit outside the window, that will keep the fan noise down.

You could couple this with a fan and filter in the far window to bring in the fresh filtered air. Might take a little to get them nicely balanced.

[Pere Casals]

You will want to have the air pulled over your trays and away from your face, then exhausted.

+1


__________________________________



In a ventilation you can blow in or blow out.

Your priority is making fumes from the wet area go directly to the extraction, if you have turbulence then fumes mix in the whole room air and this is not ideal.

So better having a fan extracting over the wet area because if you blow air in then you generate turbulence inside the room.

The input vent may have a filter, this is perfect to eliminate dust, but IMHO best choice is to also placing a fan with mild power on that filter, or to close the extraction fan when openning the door, because if not unfiltered air enters when openning door, this is YMMV, but I find very convenient to eliminate dust. Ideally you may use an HEPA spare filter (home air purifier) for the input, with a foam before it to protect it from most of the coarse dust. You can also use an spare anti-particle for the habitacle of a car.

I made flow simulations, but a good way to check if you have turbulences is using a cuban cigar (Cohiba Behike if possible :)) to see how smoke flows to the extraction vent without turbulences.

Turbulences generated by blowing in, bad situation:

https://live.staticflickr.com/1954/43374449120_70ff661bcd_b.jpg


Good flow generated by an extraction system placed in the right place, trays are vented without spreading fumes in the rest of the room:

https://live.staticflickr.com/1970/45203453631_533ee077f5_b.jpg
193949

[Louie Powell]

Any discussion of ventilation must also take into consideration two important factors. First, dust is a problem that must be addressed in the design of the ventilation. Second, it's not possible to practically seal a darkroom so that you have total control over all paths for air flow.

To me, that says that a negative pressure design is going to have problems with dust - since you can't control/filter all paths through which air enters the darkroom, there will be a uncontrolled flow of dust. So I opted to design my darkroom to have positive pressure - that is, air is taken from outside the darkroom, passed through a filter, and forced to flow into the darkroom near the enlarging station. There is a passive vent that allows air to exit the darkroom at the wet sink so that chemical fumes aren't circulated throughout the room. It also means that the flow of air through those uncontrollable channels will be outward, thereby significantly reducing the risk of dust entry via those paths.

Also, my darkroom is wired so that the main power switch at the door simultaneously turns on power to both lighting and ventilation. There are additional switches at the enlarging station to turn off the white light, and turn on the safelights. As a result, ventilation is automatically on whenever I'm in the darkroom.

The other important point is that ventilation systems can be noisy, and high ambient noise isn't really conducive to creative work. I designed the ventilation system in my darkroom to place the blower totally outside the darkroom, and to have the filtered air flow through a duct (corrugated plastic shower vent piping) into the darkroom. As a result, I can only barely hear the blower inside the darkroom.

Final thought - the darkroom in our previous home didn't have ventilation, and my experience was that I tired far more rapidly while working in that space compared with my newer darkroom. There are obviously many factors that contribute to that observation, but I believe that the improved ventilation is a major consideration.

[Pere Casals]

Second, it's not possible to practically seal a darkroom so that you have total control over all paths for air flow...

To me, that says that a negative pressure design is going to have problems with dust - since you can't control/filter all paths through which air enters the darkroom,

With negative pressure, the single uncontroled path is the slits in the door boundary, but we can use soft rubber/foam seals like those for thermal efficiency in window frames. Anyway that flow can very small to cause dust problems.

The positive pressure is very prone to create turbulences that mix the fumes in the whole room, then it requires a much higher air flow, and this may make difficult to have 20.0ºC in the lab for total consistency, and filter is clogged sooner.

Yes, the negative pressure may allow some little unfiltered flow incomming, but positive pressure requires a too high air volume for a good ventilation, so IMHO it's not the right one, to me best is negative pressure and addressing its drawback for dust control, this is providing an aceptable sealing for the room door or to place a low power fan in the input filter to have zero pressure difference. In my experience a very simple seal in the door makes the negative pressure way the right one, no odor, no fumes around, smaller vents, less (or no) noise, easier temperature control and (easy to obtain) also perfect dust control with less dirt in the filters.

IMHO positive pressure works but it cannot be recommended, what it can be recommended it's sealing a bit the door for negative pressure. Simply use light seals that will also seal (or filter, foam) air.


Do the cigar test with positive pressure, you will see how smoke is dispersed in the whole room, then test it by reversing the fan, you will see how smoke goes direcly to the output in a laminar flow without spreading.

[Bruce Watson]

So, I’m thinking to put a Doran 400 CFM fan in the window in the larger room to draw fresh air in, and a passive air outlet through a light louver in the window above the sink in the alcove to release the fumes outside while maintaining a positive pressure. (I've been told positive air pressure is important to reduce the amount of dust in the darkroom.)

Or should it be the other way around? with the passive, louvered inlet of fresh air flowing into the larger room and the fan serving to exhaust (extract) the fumes above the sink and out the alcove window?

Which is correct?

Air is compressible. As such it's much easier to pull air than to push it. Air pushes about as well as pushing a rope. Much better to put the fan on the wall exhausting to the outside. Much better to pull air out of the darkroom from above where the noxious chemicals are (typically the wall above the darkroom sink) and let the air flow past you, over the trays, and out. If needed, pull the air from above the sink through a duct to that fan on the outside wall. Let "make up air" into the building through a vent that's pretty far away from the exhaust of the fan (or you'll just end up pulling the noxious fumes right back into the darkroom).

[David Wolf]

Thanks to all for sharing their experience ~

How important is the height of the incoming air louver/fan? It would be much simpler in this room to locate the inlet louver (with or without fan) in the already existing, shoulder-level sliding window (across the room from the sink), rather than cutting a hole into the bottom of the adjacent exterior door. With the louver in the window, however, the fresh air would be incoming at about the same height as the the window above the sink on the opposite side of the room, where the fumes will exit. Would this matter much? Some recommend the air intake to be lower than the exit ~

Also, what brand/model do you use for fans, whether intake or exhaust? HEPA filter type?

Thanks again!

[Drew Wiley]

Pulling air is far more efficient than pushing it. I use a big externally-mounted squirrel cage fan on the exterior of the building. This also isolates the noise. It has a variable power control switch. An industrial unit made by Broan, not at all like an ordinary residential fan. If you use a residential type, I strongly recommend a Panasonic in-line fans with speed control. Around $400. Also squirrel-cage design and very quiet. Propeller-type fans are noisy. Of course, you need commensurate intake vents.

[Graham Patterson]

I put my extraction vent in the ceiling. It was a pragmatic choice, but less than ideal. I clears the fumes and ventilates OK, but in the winter it also removes the warm air! Since my intake is from the outside, that can be significant. Extraction behind the wet area and below head height might be better, but you also need to avoid long extraction ducts and bends in the them. That causes turbulence and reduces efficiency.

Oh, and make sure your ducts do not rattle!

My space is 8'x9'x7'6" high.

[Leszek Vogt]

In my case I have a window on the opposite side, which allows the air to enter and the amount can be controlled. There are 100s of ways to set up ducting over the chemicals (dev. area). Quiet fans would work best and there are plenty to choose from. Also, there are inline fans that help the air to push out of the duct.....but I'd never buy one of those $18 ones from homey depot or Lowes. Yes, the quality ones cost and I happen to have one on clothes drier outlet line....it's been in use for over 4yrs w/o issues.

Here is a sketch (adaptation ?) from Chris's darkroom, who is on this forum....and you can install as many fans as you desire....preferably quiet ones.

194082

Les

[wclark5179]

How long of a duration do you intend to spend in your darkroom?

In high school and college I don’t recall ventilation being used.

I would be more concerned about dust with ventilation you describe.

My wife insisted our basement bathroom, we had it finished in 2017, be made large enough to support my darkroom activities. It does have a fan but I very rarely use it. So far I have no dust issues.

[Jim Noel]

M darkroom has positive ventilation with the intake near the sink,and the outlet at the other end of the sink. Not an ideal placement of vents, but they have worked well for over 30 years. I Have forgotten the brand of the fan, but it is a squirrel cage.

[Pere Casals]

basement bathroom ... my darkroom activities. It does have a fan but I very rarely use it. So far I have no dust issues.

Many bathrooms do nothing if door is closed, if there is no additional air intake then extraction can do nothing



So far I have no dust issues.

Also no dust issues if you place filter in the air intake, a bare foam is very good, an HEPA class filter is perfect.

[William Whitaker]

David,

There's not really any correct or incorrect way to do it as long as the air is exchanged in a manner and timeliness that suits the demands made on the room.

Personally, I have my doubts about the ability of a 400CFM-rated Doran unit to adequately exchange the air in a 1200 cubic foot space. That would suggest an exchange rate of once every three minutes, assuming an 8' ceiling and if everything is working correctly. That may be enough, but for me, I'd rather have a little extra performance built in.

For the system I installed 20 years ago I built the ventilation around a surplus furnace fan that I mounted outside of the darkroom space. It pushed filtered air into that darkroom space which exited on the other side of the sink. I worked to keep flow paths as straight and smooth as possible to try to keep flow laminar and avoid turbulence as much as possible. The air entered the room behind a cabinet. Part of the laminar flow idea was to provide a clean workspace for loading film holders. Air crossed the room and over the sink to some ductwork which then directed it to the exhaust built into an outside window. The ductwork toward the window was painted flat black inside and a couple of 90º bends all but insured that no daylight could get in. Finally an exhaust vent with a spring-loaded flap kept dust, dirt, small animals, etc. outside where they belonged.

That system was great. It ran like it had a Hemi in it (which it almost did). I knew when I bought it that the fan would too powerful for the application. And sure enough it was. So I exchanged the driven pulley for one of slightly larger diameter to reduce the fan speed somewhat. It helped, but the fan was still a serious contender for a wind tunnel (which was what I did not want!). Upon turning on the fan, doors would slam shut due to the sudden air flow. And that certainly seems like overkill. But I must add that the exhaust was [necessarily] on the side of the house that was upwind to the prevailing winds in the area and they could be very strong.

Once the doors to the darkroom were shut (and myself lashed to the ship's wheel) the airflow settled into a well-behaved system. There was a constant exchange of air which felt refreshing on most days. Fumes and dust never seemed a problem.

I don't think a mass-produced, factory-built fan unit would have done what I needed. And my space was similar in size to yours. Of course, I did have the prevailing winds to deal with. But I was very satisfied with that installation and would do the same thing again if I had the opportunity.

BTW, the fan was mounted in a coat closet outside of the darkroom (formerly a bedroom) and bolted to the concrete slab floor. The closet door was replaced with a full-size board into which was mounted a 16x20" filter frame. The filter installed therein is what filtered all the air going into the darkroom. After the fan, the air entered the darkroom through a 12x12" duct cut in the wall, thence distributed into the darkroom. That helped, I'm sure, to keep noise to a very tolerable level.

It was a fun project and it worked very well. I still have recollections of going into the darkroom for an evening's work, Turning on the system and being able to feel right away the change in the atmosphere as the cool evening air pervaded my workspace.

I'm sure not being married helped.

[Tin Can]

LOL

Twice



I'm sure not being married helped.

[R.K]

David,

There's not really any correct or incorrect way to do it as long as the air is exchanged in a manner and timeliness that suits the demands made on the room.

Personally, I have my doubts about the ability of a 400CFM-rated Doran unit to adequately exchange the air in a 1200 cubic foot space. That would suggest an exchange rate of once every three minutes, assuming an 8' ceiling and if everything is working correctly. That may be enough, but for me, I'd rather have a little extra performance built in.

For the system I installed 20 years ago I built the ventilation around a surplus furnace fan that I mounted outside of the darkroom space. It pushed filtered air into that darkroom space which exited on the other side of the sink. I worked to keep flow paths as straight and smooth as possible to try to keep flow laminar and avoid turbulence as much as possible. The air entered the room behind a cabinet. Part of the laminar flow idea was to provide a clean workspace for loading film holders. Air crossed the room and over the sink to some ductwork which then directed it to the exhaust built into an outside window. The ductwork toward the window was painted flat black inside and a couple of 90º bends all but insured that no daylight could get in. Finally an exhaust vent with a spring-loaded flap kept dust, dirt, small animals, etc. outside where they belonged.

That system was great. It ran like it had a Hemi in it (which it almost did). I knew when I bought it that the fan would too powerful for the application. And sure enough it was. So I exchanged the driven pulley for one of slightly larger diameter to reduce the fan speed somewhat. It helped, but the fan was still a serious contender for a wind tunnel (which was what I did not want!). Upon turning on the fan, doors would slam shut due to the sudden air flow. And that certainly seems like overkill. But I must add that the exhaust was [necessarily] on the side of the house that was upwind to the prevailing winds in the area and they could be very strong.

Once the doors to the darkroom were shut (and myself lashed to the ship's wheel) the airflow settled into a well-behaved system. There was a constant exchange of air which felt refreshing on most days. Fumes and dust never seemed a problem.

I don't think a mass-produced, factory-built fan unit would have done what I needed. And my space was similar in size to yours. Of course, I did have the prevailing winds to deal with. But I was very satisfied with that installation and would do the same thing again if I had the opportunity.

BTW, the fan was mounted in a coat closet outside of the darkroom (formerly a bedroom) and bolted to the concrete slab floor. The closet door was replaced with a full-size board into which was mounted a 16x20" filter frame. The filter installed therein is what filtered all the air going into the darkroom. After the fan, the air entered the darkroom through a 12x12" duct cut in the wall, thence distributed into the darkroom. That helped, I'm sure, to keep noise to a very tolerable level.

It was a fun project and it worked very well. I still have recollections of going into the darkroom for an evening's work, Turning on the system and being able to feel right away the change in the atmosphere as the cool evening air pervaded my workspace.

I'm sure not being married helped.



In accordance with ASHRAE, the darkrooms required 20-30 cfm of fresh air per person. To have 1 air change per 3 min. giving you 20 air changes per hr. This is craaazy big number and really overdesign. For example the typical hospital patient room for people with EBOLA and other dangerous diseases by the code required only 12, max. 15 air changes per hr. Not many chemical labs having 20 air changes per hr. requirements. And in the labs usually in order to limit amount of exhaust air, special hooded cabinets used and exhaust working only when the cabinet door open and dangerous vapor may enter the room space. The darkroom with 20 air changes /hr. exhaust and direct fresh air intake from outside, without dedicated air conditioning unit specifically provided for that particular room will be hot in summer and cold in winter. Drafting air from the rest of the house also not perfect idea, because the regular home air conditioning system don't have any fresh air intake at all. Standard home air conditioning system designed just to circulate the same air and heating or cooling it. It assumed that in the house fresh air can get through the doors or windows. Removing air from the house will required to kip some window open, and house unit will work more often then usually, and because the fan of the unit designed to circulate the air through the entire house the electrical bill will show some additional charges. If you not trying to design in your house a hospital operating room where you will be printing photographs don't do 20 air changes per hr. exhaust. In order to kip you room clean from the not so dangerous vapors just build a hood above the sink, size the hood opening same as the area of the sink, run the duct from the hood to outside and provide the exhaust fan. If you figure the capacity of the fan as 1.2 to 1.5 or maximum 2 cfm per square ft. of the area of you sink, the room will be free of any chemical contaminations even if you will work there 24/7 without coffee brakes.

[thomas ciulei]

those are good tips by R.K.
about dust entering darkroom, think about automotive square filters. they do a great job.
in any case dont blow air into darkroom, suck it out.
radial fans do a great job, you can hook them up to pvc pipes with multiple intakes above the wet/chemical area if you have no room for a proper hood. check my post in post-your-darkroom area of forum. i can send additional pics if you need.
my fan exchanges air volume 10x hour, never smells like chemicals in the room.
cheers & good luck

[angusparker]

The key as far as I have found is to have the air come in over your head height (preferably across from your trays) and go out at waist height behind your trays. That way you are never breathing fumes because the travel of air direction is downwards away from your nose. This guy makes plastic upside down V shaped vents to uptake the air from just above your trays. http://www.eepjon.com/Drvent.htm Scroll down to see the pictures and read the advice. I have two of them and found they work very well. I filter the air intake and push the air in, then I suck it out and send it to the roof line. That's a bit over the top but I'm in an urban setting and don't want to piss off the neighbours with smells, or send Pt from historical processes anywhere near people (even if its a tiny amount). So abundance of caution.

[Pere Casals]

go out at waist height behind your trays. That way you are never breathing fumes // http://www.eepjon.com/Drvent.htm

True, this is perfection...

194433

[Luis-F-S]

It’s not rocket science. Put an exhaust fan over the sink and put a filtered intake grill behind you on the opposite wall. That’s it!! Or you can loose sleep over the details.

[Pere Casals]

It’s not rocket science. Put an exhaust fan over the sink and put a filtered intake grill behind you on the opposite wall. That’s it!! Or you can loose sleep over the details.

Yes, but if unsafe chem is used then that design pointed by Angus it is the good one, not that difficut to build, and extremly effective.

It all depends on the chem we use, for common chem it's not necessary that optimal design, for some chem around we should do things in the optimal way, which is that design.

[Timmyjoe]

Do you all live in temperate climates?

It seems like the systems discussed here move a lot of air, and if you are drawing air in from outside and then exiting the "dirty" air back outside, how are you keeping the temperature in your darkroom anything other than the outside air temp? I think that would work fine up here in Northern Illinois, for about two months out of the year. Otherwise the darkroom would be freezing cold in winter and boiling hot in summer.

Best,
-Tim

[Tin Can]

I use inside air here in Illinois, but draw it outside.

I also use low pressure, low volume and safer chems.

[Maris Rusis]

My present (and best) darkroom was designed to solve the ventilation problem by leaving it out entirely. I use odourless developers, odourless stop bath, odourless fixer, odourless hypo-clear, and odourless archival washing with water. Some of this chemistry costs a bit more than the cheapest and nastiest but it's worth it. Instead of forced ventilation I installed a reverse cycle air-conditioner with a good filtration system. The air always smells good, no dust, and no boiling in summer and freezing in winter. And in the course of a 5 or 6 hour session the darkroom door gets opened and closed many times to take pictures out, call a colleague in for an opinion, take a coffee break, etc. No stale air for me, please.
https://live.staticflickr.com/5523/14432614805_8cd505ac54_c.jpg

[angusparker]

Do you all live in temperate climates?

It seems like the systems discussed here move a lot of air, and if you are drawing air in from outside and then exiting the "dirty" air back outside, how are you keeping the temperature in your darkroom anything other than the outside air temp? I think that would work fine up here in Northern Illinois, for about two months out of the year. Otherwise the darkroom would be freezing cold in winter and boiling hot in summer.

Best,
-Tim

Yes, temperate. San Francisco temperature rarely deviate from around 60F. Longer term I want to set up a darkroom where the outside temp varies from 0 to 110F through the year. No idea how I would manage that, except the formats and trays would be for 8x10 not ULF sizes which makes a big difference.


Sent from my iPad using Tapatalk Pro

[Andre Noble]

Stock up: They wont be available forever https://www.adorama.com/l/?searchinfo=darkroom+fan

[Renato Tonelli]

It’s not rocket science. Put an exhaust fan over the sink and put a filtered intake grill behind you on the opposite wall. That’s it!! Or you can loose sleep over the details.

This is essentially what I have just finished installing in my home darkroom: a passive Doran double-louver above the door and opposite the sink and an exhaust system based on Edward's Engineering. The exhaust vents are slots at the back of the sink and pull the fumes quite efficiently; the exhaust fan is the same one used by Jon Edwards (from Grainger). If I had the money and space for it, I would have simply bought the whole thing from him (my sink was supplied by him). BTW - he is very knowledgeable about this and very helpful.

And - I once worked in a 'professional' darkroom with air blown in and what I got was mostly headaches.

[Luis-F-S]

Stock up: They wont be available forever https://www.adorama.com/l/?searchinfo=darkroom+fan

Have a spare for when needed

[Rob Vinnedge]

My system actually does push air, but the air flow is quite directional not unlike laminar flow in a clean room. I have a powerful roof mounted blower that blows into my darkroom through two HEPA filtered ceiling vents at opposite ends of my 9"X20" space. I have a 12" dia. duct pipe positioned vertically over my stop/fix/chem. mix area in the middle of my 19" sink on the opposite wall from the two ceiling vents. This gives me fresh air at all times, a positive pressure in the room, and extremely efficient venting of fumes and odors. The air moves very quickly out the duct pipe. The positive pressure also efficiently eliminates the dust problem and the remote roof fan eliminates noise. I also have the fan on a rheostat for greater control over air flow. When not in use, I tape a cardboard to the duct vent in order to prevent random air currents from occurring.


195034 195035 195036

[Tin Can]

Nice DR, looks like it is institutional from the doors visible.