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Thread: Advice for installing louvers and a fan for a darkroom shed?

  1. #1

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    Advice for installing louvers and a fan for a darkroom shed?

    2020 has been a dumpster fire, but among the not so terrible bits is that I managed to get a 10x10 shed in the backyard to be used as my new darkroom! It's quite an upgrade from the bathroom!

    Lots of work to be done still - insulation in particular. But one thing has me a bit hung up. I bought Doran louvers as well as a louver/fan combo. The fan seems pretty obvious on how to install as it is thick enough where the rear end of it (the bit where you can attach a pipe) would go out to the outside with the louvers facing inside.

    But the regular louvers have me confused. They are only I dunno 2-4" thick - not enough to go through whatever I end up finishing the walls with (probably sheetrock due to cost - originally I was just fine with OSB but that stuff is expensive at the moment). So should I point the louvers to the outside and make just a hole with a vent cap for the inside? Should I get another one so I have louvers on both sides? Should I just install the fan and let the air come in from the inevitable cracks in the door and floor (I was worried that might bring in dust) Am I doing it all totally wrong? :P

    The instructions are super vague on how I should be going about this.

    Other thing I hadn't considered...when I'm not toning I don't need a crazy amount of airflow all the time. So been thinking about how to cover them up when not in use to help with heating or cooling the space.

    Any ideas or thoughts anyone might care to share?

  2. #2

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    The first rule is if you want air going out, you need temperature and humidity controlled air coming in. I was gifted a Doran setup like you have it helps but if you are using sulfide toner, or strong selenium, it's barely adequate.
    I bought a small dust collection system blower at Harbor Freight, small for sawdust, enormous for my 12x20 darkroom. My advice is to install the blower part in the cavity in the wall, box it in with some plywood or 1x4 etc. Then install your louvers on the interior 1/2" or 3/4 " wall material to make it light tight you can get a quality metal dryer vent outlet to attach to the round duct of the blower,on the outside. It has a flap that opens when the blower is on.

    I open my darkroom door, when I turn on my blower, even then you need to allow outside air in . I have to be careful not to trip the switch on the furnace that detects negative pressure.

    I worked in an analytical lab with big fume hoods, if it was cold outside the makeup air would hit the exhaust and condense sulfuric acid inside the hood. Big mess, hopefully you live in a warm climate. I haven't done sulfide toning for some time.

  3. #3

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Huh whoa today I learned industrial dust blower/filters exist! Something like this? I wonder if I can use that inside as well to keep dust to a minimum when, say, I'm drying prints or film? For film I was going to build a small box with a HEPA filter and a bulb or fan for sheet films; for roll films I might just bring them inside to hang in the bathroom.

    Anyways back to it! To make sure I have it right - the industrial blower would be pushing air IN or attached to the louver/fan combo on the exhaust? I assume the former so I can get positive (and filtered) airflow. You're right about temperature/humidity - this is exactly what I was worried about if I, say, wanted to print and tone all at once. In this case I couldn't temperature control the air coming in (or humidity) and would have to rely on the AC or heater to try and make up the difference.

    Outside of selenium, I was thinking I'd use the vent as needed for normal printing sessions just to suck out some of the fixer fumes. It hasn't been an issue so far (certainly far superior to my bathroom...).

    If I keep my toning sessions separate and do them in batches, I can always do those with the door open during the day to help. I was previously doing these in my garage (with the garage door open) and it worked but was a mess with the wash water and was a special day so I'd stack up several prints. This works but I'd like to do smaller more frequent batches.

    I'm in South Texas so yep mild winters typically, though at night it can get colder than ideal for BW chemistry. In the summers it's quite warm at night.

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    I have never liked forced air drying for films. I would just use distilled water and 1 drop of LFN or PhotoFlo. Too late to say more now. Keep the air exchange to a minimum. Humidity control is critical. Dehumidifier, will overheat your shed, you may need a tiny AC unit.

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Hey cool 3D printing

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    Louie Powell's Avatar
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    Re: Advice for installing louvers and a fan for a darkroom shed?

    It's nearly impossible to seal a darkroom so tightly that dust-laden air can't inflitrate around doors, receptacles, plumbing penetrations, etc. So I think that the best approach is to use a 'positive pressure' design in which air is forced into the darkroom, and allow to flow naturally out by way of a louver and all of those incidental and uncontrollable paths. But if you are bringing air in, you need to make sure that it is the kind of air you want. But the fact that there is only one air path that you need to be concerned about means that controlling that air is relatively simple.

    My darkroom is in the basement, and has air entering via a louver located near the enlarger station. That air is channeled through a length of standard plastic bathroom vent hose from a fan located outside the darkroom. The fan itself is a standard computer fan - it doesn't need to blow a gale, just force air flow into the darkroom. It is mounted in a box constructed by installing wood blocking between a couple of floor joists, and with the seams sealed so that the only way that air can get into the box is through a HVAC filter mounted on bottom of the box. Note, however, that this box could just have easily been constructed in the walls of the darkroom - I simply had the advantage that because my darkroom is in the basement, I could easily put the box outside the darkroom to minimize noise from the fan.

    I have a master power switch next to the darkroom door that switches on power to all of the lights. There is one receptacle that is also on that switched circuit to power the fan; it comes on and runs whenever I'm in the darkroom. I have separate switches that control both the white light and safelights.

    The fact that air is being forced into the darkroom means that air pressure inside the darkroom is slightly greater than outside the darkroom, which means that air cannot flow in through the many incidental penetrations through the darkroom walls and ceiling. Instead, air flow through those penetrations is always out of the darkroom. I did install a louver on the wall behind the darkroom sink that allows greater flow at the point where fumes are released from chemicals.

  7. #7

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Long ago I had a darkroom in a free standing 2 car garage. In Memphis the weather can be pleasant often at night and I would open the door at night when printing. Now my darkroom is in the basement and I use one of the Doran fans like you have. It works but is loud. I plan to change it soon, but have not decided on how I will replace it.
    Ron McElroy
    Memphis

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Quote Originally Posted by Louie Powell View Post
    The fact that air is being forced into the darkroom means that air pressure inside the darkroom is slightly greater than outside the darkroom, which means that air cannot flow in through the many incidental penetrations through the darkroom walls and ceiling. Instead, air flow through those penetrations is always out of the darkroom. I did install a louver on the wall behind the darkroom sink that allows greater flow at the point where fumes are released from chemicals.
    Yep this is what was taught from building PCs - you want slight positive pressure (wherein there are more fans pushing air in than pulling out) to prevent air from getting in from other parts of the case. The air that does come in you can then filter for dust. In practice, this doesn't seem to fully eliminate dust but it sure does help inside a computer case.

    For the darkroom, the louver/fan seems to be sucking air from the light tight vents and out the back - a pull rather than push. I could flip it around though the instructions do show it's meant to extract. So yep I kinda expected that might cause problems with negative pressure and dust.

    Also glad you like the 3D printing stuffs!



    Ron, some alternatives I have seen are Panasonic vent fans. You'd have to figure out how to make it light tight, but they're both quiet and seem to move a lot of air (but certainly not the cheapest fans on the market).

  9. #9

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Yes, the Panasonic bathroom vent fans are amazing, quiet! My blower system is rarely used. I can tone with selenium without a problem. I use citric acid stop and rapid fix. Film development color and black and white is run on a Jobo CPP3, with a lift. Modern color chemistry doesn't bother me. Air filtration, to be effective, can be, necessarily quite complicated. In your small shed not so much.
    There's a different approach entirely. I have a 3M double respirator, it's a very good setup, has carbon and acid fume removal capabilities. I was making silver nitrate, and I had it just in case my at that time Doran blower failed. It all came out all right, no problems but it works on stinky toner as well.

  10. #10

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    Re: Advice for installing louvers and a fan for a darkroom shed?

    Hmm respirator is a good idea. So far BW hasn't been bad. I haven't tried RA4 yet but I tend to do that in a print drum though I usually keep the chemicals I'm about to use in open beakers in a water bath. It wasn't bad in my bathroom darkroom though. For BW, I usually cover my fixer trays (I do two bath fixing typically) when I'm not using them. Having a means to occasionally extract fumes I think would probably be sufficient there.

    It's really the selenium. The ideal is to print and tone in the same evening so it's done. I think for that, I'd need to consider some sort of active solution. Not the worst if I have to tone on a subsequent day though. Actually I'm going to try toning for the first time in the new space probably today so I can gauge how convenient it is to do so - I'd imagine it's far more convenient than using my garage.

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