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Thread: Darkroom Venting

  1. #1

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    Darkroom Venting

    Some time back I posted pics of my "last darkroom" 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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  2. #2

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    Re: Darkroom Venting

    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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    Last edited by Luis-F-S; 21-Feb-2021 at 13:39.

  3. #3

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    Re: Darkroom Venting

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

  4. #4

    Re: Darkroom Venting

    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.

  5. #5

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  6. #6

    Re: Darkroom Venting

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

  7. #7
    Vaughn's Avatar
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    Re: Darkroom Venting

    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.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  8. #8
    Jim Jones's Avatar
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    Re: Darkroom Venting

    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.

  9. #9

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    Re: Darkroom Venting

    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.

  10. #10
    Drew Wiley
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    Re: Darkroom Venting

    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.

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