Darkroom Venting

[Jess C]

Some time back I posted pics of my "last darkroom" (https://www.largeformatphotography.info/forum/showthread.php?156082-My-Latest-And-Probably-Last-Darkroom&highlight=Jess) and there were several questions about my venting. When I built and installed my darkroom sink I built and installed a box (aka "shelf") unit above the sink and then used two bathroom exhaust fans to move enough air for my space. The box was necessary to hide the vent hoses and all the electrical wiring that is feeding my exhaust fans, and inspection light. And since the exhaust fans are installed up underneath the soffit and directly over the processing trays the fumes get sucked up and away and through a vent hose that goes into the attic which then gets drawn out through the attic vents to the outside. It seems to work quite well and I believe the air exchange rate is at 110 CFM per fan for a combined 220 CFM (just over 5 minutes for a complete exchange of air or about 11 exchanges per hour if my math is correct)which seems to handle my 11x12 darkroom with a 9 ft ceiling well enough.

I bought the fans from Home Depot and so far I am quite happy with their efficiency and low noise level. Not super quiet but quieter than most exhaust fans I have experienced. And with music playing in the background the fan noise is not an issue.

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[Luis-F-S]

I did something similar, though my box is higher up from the sink. My fans are also Doran/Lowell 600 CFM fans, so a bit noisier. I have them on a speed control rheostat, so I can lower the rpm and noise. The exhaust pipe goes straight out the exterior wall. There is an intake louver (two actually) at the opposite end of the room. The photos were made during construction and before the space was completely finished.

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[Jess C]

Pretty much how I did mine except the exhaust pipe goes straight through the ceiling and into our large attic space.

[Conrad . Marvin]

Just getting ready to vent, do you have information on the Home Depot fans? They sound perfect for the space that I have and if they are somewhat quiet, that would be a help. Thanks.

[Jess C]

https://www.homedepot.com/p/Broan-NuTone-InVent-Series-110-CFM-Wall-Ceiling-Installation-Bathroom-Exhaust-Fan-A110/206620816

[Conrad . Marvin]

Thanks, looks as if there are many options available and they will fit in the space that I have.

[Vaughn]

Dang....I was ready for someone to complain about their darkroom.

Looks sweet, Jess. Luis' also, but one will have to be careful not to lean over the sink and have one's head in the flow of fumes up to the fans.

My only consideration is that tends to be easier/more efficient to pull air than it is to push it. Fans might work a little better when placed at the exhaust end of the system. Any comments on that by any of our ventilation experts?

I am considering putting the fan on the other side of the wall -- keep the noise out of the darkroom altogether.

[Jim Jones]

I'm certainly no export on the subject, but believe if a darkroom is fairly airtight, it is better to suck air into it through filters and exhaust from over the sink as done by previous posters. My darkrooms were never set up that well, but it did make me become good at spotting prints.

[Jess C]

I'm sure there are better alternatives but I think that as long as fresh air is drawn in and drawn out through an exhaust system it will serve the purpose. The main purpose is to expel the fumes and not let the air in the darkroom to become stale or stagnant and I believe my setup does that well enough as I have not noticed any staleness to my darkroom and believe me, I have experienced this in other darkrooms.

[Drew Wiley]

Pulling air is always more efficient than pushing it; and another advantage is that any noise is isolated outdoors. There are also efficient fans which can be installed intermediate in an attic space. But these deluxe options are also more expensive. Squirrel-cage fans that can be mounted between wall or ceiling studs are easier to install; but one still needs to be conscious of the air ducting being planned to prevent light coming in. Worst are loud propeller fans. I believe in having a surplus of extraction capacity, which can either be boosted if necessary or dialed down with an RPM controller when that is more appropriate.

When selecting a fan, think about basic issues : A fan will be pushing against more hydrostatic pressure outdoors in rainy or humid conditions than in dry weather. You also have to factor the amount of air friction involved with ducting which needs to be slightly convoluted just to keep light from piping in. Convenient corrugated ducting causes more air friction resistance than smooth ducting. Don't undersize your ducts. All these issues mean that if you think you need 100 CFM based on air exchange expectations, get a 200CFM fan instead, because you'll easily lose half the efficiency due to factors I noted above. If you are dealing with riskier chemicals like concentrated glacial acetic acid or color printing chemistry, the ability to rapidly exhaust the fumes out is important.

Other important things : have enough make-up air coming in from light-tight exterior vents to efficiently replace what you're extracting. If you don't need to draw in a large volume of air in cold winter weather, then just mount temporary covers over surplus intake vents. Arrange the airflow so it moves away from you across the sink toward the intake ports or fans.

A 200CFM basic 4-inch duct squirrel cage bathroom-style quiet fan from a premium manufacturer like Panasonic will run you around $250, with maybe another $50 for a dedicated speed control. Expect to pay double that for a more powerful 450 CFM inline attic squirrel cage (which is often the cheaper option because just one of these can handle multiple ducts). A big exterior industrial squirrel cage will cost considerably more; but you could also install multiples of small exterior fans if desired. Overall, you get what you pay for;
cheaper brands can obviously be used, but won't last as long.

[Vaughn]

On top of that, if one has the air flow keeping fumes from one's head, any movement of bodies in the room will disturb the air flow -- minor issue.

[Richard Wasserman]

I would like to add that dumping warm moist air into a cold attic is not best practice. It is much better to exhaust to the great outdoors so moisture doesn't condense and cause havoc with the building. I'm sure it depends where you live, and that it may be a bit temperature dependent, but it is currently in single digits here and all my vents in the house go outside.

[Daniel Unkefer]

https://live.staticflickr.com/65535/50376433896_a8e48dc3e5_z.jpg (https://flic.kr/p/2jKAoH7)HRU Wash Step Dental Clips 2 (https://flic.kr/p/2jKAoH7) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr

I used a driveway drain glued to PVC pipe and the largest bathroom fan I could find. It does pull odors outside rather well.

https://live.staticflickr.com/65535/50408776801_c42a7792dc_z.jpg (https://flic.kr/p/2jNsa8p)Kodak 3F Basket Line 1 (https://flic.kr/p/2jNsa8p) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr

Here's the other side of it. My Contractor and also Electrician put this together with my input. It vents out extreme top left.

[John Layton]

Here is my “backdraft” ventilation setup:
Photo 1 - two runs of 6” flexible heater pipe, running from two 4x12 boxes cut into the sink shelf, and up to a "Y" connector and up to the fan:

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Photo 2 - individual shutoffs for each run:

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Photo 3 - Variac transformer, note power level - which is where I typically set this for film and prints. When doing more toxic procedures I turn this up a bit. Full power (like a hurricane!) is hardly needed - but nice to know its there:

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Photo 4 - closeup of fan, purchased at Home Depot. Cannot ascertain/remember model, max CFM’s (quiet and powerful), but cost of fan was about 140.00, Variac (from Amazon) was 50.00, Piping, etc., about another 75.00:

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Finally, this system vents out of a 6" weather head, the hole for which I cut through the band joist/siding.

[Wayne]

Couple of small 4" surplus muffin fans can output 200cfm for $5 each.

[Drew Wiley]

Wayne, have you been reading one of those old Popular Mechanics articles telling you how to build your own nuclear submarine using recycled washing machine parts?

[Wayne]

No, but 20 years ago when I set up my darkroom someone mentioned surplus muffin fans for a few pennies a piece and I built my darkroom vent with 2 of them. Works great.

[Drew Wiley]

How far are you venting (duct configuration), Wayne?

[Wayne]

My fans are in the window directly behind my sink. No ducting at all, just a light trap

[Drew Wiley]

Bingo. Thanks. Nothing remotely related to true 250 extraction, but evidently useful for simpler applications. I had something similar exchanging air in a makeshift film drying cabinet, with nothing other than basic "permanent" coffee filters glued over the intake and outlet ports to prevent dust.

[Wayne2]

Bingo. Thanks. Nothing remotely related to true 250 extraction, but evidently useful for simpler applications. I had something similar exchanging air in a makeshift film drying cabinet, with nothing other than basic "permanent" coffee filters glued over the intake and outlet ports to prevent dust.


Not sure what your "Bingo" point is. I was just mentioning a cheaper source of efficient fans for do-it-yourselfers.

[Drew Wiley]

Efficient? Not by any HVAC standard by which things are conventionally classified. Useful perhaps under limited conditions, yes, as you have demonstrated, but not realistic under most darkroom circumstances, which necessarily factor ducting, long-term durability, and sometimes, formal building code inspections. Hardly suitable for color darkroom either, where fumes can be distinctly unhealthy. Then there's the hydrostatic weather and humidity issue I noted earlier.

But I do understand the need of affordable options. My first "darkroom" setup consisted of the enlarger in a bedroom with a blocked out window, and a drum processor in a small adjacent bathroom with the window wide open and an ordinary stand fan next to it. The color drums were light tight and loaded in the bedroom. All the chemistry was done in the bathroom. But even that was better than where I learned to do sheet film development for sake of masking in a filthy furnace closet, which had the necessary legal floor air vent.

[Wayne]

They may not be for everyone but they are plenty efficient in cost, airflow and power use, and they work just fine for color. They can be a bit noisy, but I like white noise.

[Drew Wiley]

I have R23 insulation in the sink and film rooms, which makes my darkroom itself the quietest place to be on weekends. I have neighbors over the back fence whose whole point for existence seems to be to get roaring drunk on cheap beer on game days, shout as loud as they can, mostly obscenities, and play loud "music" (also mostly obscenities). Even their cats left and adopted us instead. But now they've got a pet raccoon with a conspicuous beer belly of its own - friendly tubby feller, but probably due for coronary bypass surgery to clear all the french fry grease clogging things up. He's the only member of that group covered with fur instead of tattoos.

[Mike in NY]

For fresh air intake I use a light-tight vent installed in one of the darkroom's two doors. For exhaust, I use 6" duct tubing that hovers above the sink where I tend to do my fixing. The duct is positioned in a 6" diameter hole cut into a shelf above the sink. From there it goes straight up, then makes a curved 90 degree turn to the right and runs until it reaches the wall. Then it makes another 90 degree turn and runs down to an outside vent. There are three separate in-line duct fans installed within the tubing: the first one is just inside the opening above the shelf; the second fan is about half way down the first horizontal path; and the third fan is at the vent exit. They are easy to install; you just slice your tubing and fit it onto either end of the fan's housing, and run the cord to an outlet. I got my fans at Home Depot, but they are available from Amazon and other providers. They come in different sizes for 4", 6" or 8" tubing. The 6" fans I use have a speed of 2960 RPM, and a rated air flow of 240 CFM. Is it enough ventilation? I really don't know, but I know that it helps, and the fans are very quiet.

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[John Layton]

While these duct-vent "helper" fans might not be powerful enough (for darkroom venting), especially when placed at the beginning of such a long and curvy run, I think the fact that you have three of these in succession would make this sufficiently effective.

Does this vent to the outside through a weather-head equipped with an aluminum "anti backdraft" flap? If so, how much does this flap deflect upwards when the fans are on? (I'd worry if this deflection, when measured at the bottom of the flap, were less than about one half inch).

And a test: place a tea-saucer on your sink bottom...maybe about a third of the distance between your faucet and the vent opening - light a match and blow it out...then quickly place it on the saucer - and watch what happens to the smoke. (alternately, use a candle) Then...try the smoke-test from the other end of the sink. If your vented darkroom door is where it should be in this picture (off to the right, furthest from the fan), then the smoke, while it may take awhile to get there...should still be pulled towards the vent.

You might also want to try taping some very thin strips of tissue to the inside-top of your darkroom door-vent, to see that these deflect enough to give you confidence that your vent system is powerful enough to overcome enough air resistance so this system can be effective.

A final test: after your darkroom is up and running for awhile, leave it for awhile (lunch break?), then come back and see if you are greeted with a strong waft of fixer. If so, you might need more power in your vent system.

In any case...I'm also assuming that you arrange your trays to place the fixer closest to the vent, unless your developer happens to be particularly toxic.

[Mike in NY]

John, you've made some cogent points. As mentioned above, the first fan is positioned over the space where I perform my fixing. When I set this up, I tested the uptake draw with a tissue held beneath the first fan opening, and it pulled the tissue upwards. (I also lit and blew out a match, but it didn't really produce enough smoke for me to get a good sense of how powerful the intake was.) I haven't tested the strength of the intake flow at the light-tight vent in the door at the other side of the room; that's something I'll try - thanks for the suggestion. The exit vent in the wall does not have an anti-backdraft flap, as it is deeply recessed into the very thick foundation of the home, within a deep 30" x 30" by 60" window well, which is covered by hinged, iron grating (these enormous window wells are a most unusual feature, but our 94-year old home has several of them, all with operating drains in the base of them). So there is no resistance to the outflow of air from a flap, which I agree would have been an impediment.

[Wayne]

While these duct-vent "helper" fans might not be powerful enough (for darkroom venting), especially when placed at the beginning of such a long and curvy run, I think the fact that you have three of these in succession would make this sufficiently effective.

Does this vent to the outside through a weather-head equipped with an aluminum "anti backdraft" flap? If so, how much does this flap deflect upwards when the fans are on? (I'd worry if this deflection, when measured at the bottom of the flap, were less than about one half inch).

And a test: place a tea-saucer on your sink bottom...maybe about a third of the distance between your faucet and the vent opening - light a match and blow it out...then quickly place it on the saucer - and watch what happens to the smoke. (alternately, use a candle) Then...try the smoke-test from the other end of the sink. If your vented darkroom door is where it should be in this picture (off to the right, furthest from the fan), then the smoke, while it may take awhile to get there...should still be pulled towards the vent.

You might also want to try taping some very thin strips of tissue to the inside-top of your darkroom door-vent, to see that these deflect enough to give you confidence that your vent system is powerful enough to overcome enough air resistance so this system can be effective.

A final test: after your darkroom is up and running for awhile, leave it for awhile (lunch break?), then come back and see if you are greeted with a strong waft of fixer. If so, you might need more power in your vent system.

In any case...I'm also assuming that you arrange your trays to place the fixer closest to the vent, unless your developer happens to be particularly toxic.


I was wondering how much resistance the great length of ducting and each successive fan creates. Common sense says it would work fine but common sense is often wrong. You'd almost need an aerospace engineer to figure out the actual efficiency of some darkroom vent systems

[Keith Fleming]

As a side issue when constructing your exhaust fan system, give consideration to what covers the outside end of your exhaust pipe. Some of these covers include a single round flap that may not close completely when the fan is turned off. I had one of these, and starlings started building a nest inside, which I had to clean out by hand. I replaced that cover with one with multiple louvers that fully closed, and had no more starling problems.

That darkroom, by the way, was on the plans used by the home builder. Since new homes are more tightly sealed, the building code here requires each house to have a "whole house fan" to prevent the buildup of stale air in the home. I requested the plans for the house to specify a whole house fan for my darkroom that vented outside. The door to the darkroom included a light-tight air inlet from B&H. Once the starling issue was solved, it worked great for the years I owned that home.

Keith

[Luis-F-S]

Whatever type of fan you use, it will be better than not having an exhaust fan. That's my take on it. If you can get the # of air changes per hour recommended in the Kodak guide, great, if not, it's better than nothing.

[MrFujicaman]

[QUOTE=Drew Wiley;1588154]I have R23 insulation in the sink and film rooms, which makes my darkroom itself the quietest place to be on weekends. I have neighbors over the back fence whose whole point for existence seems to be to get roaring drunk on cheap beer on game days, shout as loud as they can, mostly obscenities, and play loud "music" (also mostly obscenities). Even their cats left and adopted us instead. But now they've got a pet raccoon with a conspicuous beer belly of its own - friendly tubby feller, but probably due for coronary bypass surgery to clear all the french fry grease clogging things up. He's the only member of that group covered with fur instead of tattoos.[/QUOTE

The raccoon is most likely the smartest one over there...

[Vaughn]

I have R23 insulation in the sink and film rooms, which makes my darkroom itself the quietest place to be on weekends. I have neighbors over the back fence whose whole point for existence seems to be to get roaring drunk on cheap beer on game days, shout as loud as they can, mostly obscenities, and play loud "music" (also mostly obscenities). Even their cats left and adopted us instead. But now they've got a pet raccoon with a conspicuous beer belly of its own - friendly tubby feller, but probably due for coronary bypass surgery to clear all the french fry grease clogging things up. He's the only member of that group covered with fur instead of tattoos.

I was wondering when we were going to get to actual venting!!:cool:

I have not blocked under my house yet -- too much work under there still to do. Raccoons and skunks move in -- then quickly move out. Seems like they do not appreciate the speakers turned downwards on the floor with the "Latest Hits of the 80s, 90s and More!" played at full bass (w/boost) and volume about 8" directly above their heads randomly through the day/evening. pillows and blankets over the speakers so I don't have to listen to it much.

Edit -- tried it with rats -- they just raided the fridge for beer and had a dance party....

[Drew Wiley]

Well, raccoons do have sensitive hands and fingers, as well as superb night vision. Maybe I should train one to develop sheet film. But I'm afraid they'd try washing snails in the pyro. Sure made a muddy mess in the cat's water bowl last night; but at least they were on the right track to a staining developer.