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Building a Darkroom: Ventilation
Contents
What kind of ventilation do you needInstalling a fan for ventilation
Tools
Materials
Construction
Installing an air conditioner
Tools
Materials
Construction
Comments
What kind of ventilation do you need, Negative or Positive Pressure?
According to some photographers, you should have positive pressure ventilation, others say you should have negative pressure. There are advantages and disadvantages to both.Positive Pressure
- Any dust in the room is pushed out through minor air leaks
- The fan must have a filter, and the filter must be cleaned regularly
Negative Pressure
- The fan can be located near the sink, where it will extract fumes from chemicals directly, and thus faster than a positive pressure system
- No filter is required on the fan
My preference
I prefer an equilibrium, I use both a positive pressure fan and a negative pressure fan at the same time. I do this because I believe the purpose of ventilation is to remove the fumes, but I don't want to be sucking dirt and dust in from outside the room.- I use an air conditioner which blows air in
- and an extractor fan which pulls fumes out
- the fan is near the sink, so fumes are pulled out quickly
- the air conditioner has the added benefit of cooling the room in the summer
Installing a fan for ventilation
Selection criteria
- The volume of air must be sufficient to cycle the air in the darkroom at least 10 times per hour. To calculate this number, multiple the room dimensions and divide by 6 (a 4' by 6' by 8' room is 192 divided by 6 is 32 cubic feet per minute (cfm). When buying a fan, get one that does at least that many cfm (my 8x8x8 room uses 100cfm).
- The best fans I found were ceiling mount bathroom fans, the come with a louver, and are built into a metal box, with tabs for nailing onto 2x4 studs.
- You can mount this fan in the wall or make it into a portable unit, if you use the portable unit, you will still need a way to vent through a wall to the outside. I recommend in the wall, it is much simpler!
Tools
- framing hammer or screwdriver
Materials
- Fan, described above
- Framing nails or screws
- Romex
- Switch
Construction
- Locate the stud you where you will attach the fan
- Screw or nail it in place
- Connect the wiring to Romex, and run the Romex to the switch you are going to use to control the fan, connect to the switch.
- When you put up the drywall, put in an opening on the other side of the wall, in the same cavity, about 4 feet away, to act as a light baffle. As you see at right, the air will travel through the wall, but light (which doesn't bend) won't enter the darkroom
Installing an air conditioner
Tools
- framing hammer
Materials
- Wall or window air conditioner
- Framing nails
- 2x4 lumber
Construction
- Locate the studs between which you will be placing the air conditioner.
- Remember to put it near an electrical outlet
- Allow room on top beside the air conditioner for the face grill!
- Cut a 2x4 to fit between these studs, and nail it in place, keep it level,
The air conditioner will sit on top of this cross member.
Note: if you are unable to nail into the end, it is very difficult to toenail a cross member and keep it perfectly level, so instead, cut a small block and nail it below, or above, the cross member, and attach the cross member to the block
- Cut and install another cross sill which will be at the top of the air conditioner. Make the opening about 1/4" larger than the A/C unit.
- If the opening is wider than the A/C unit, cut a vertical member to fill up the gap, leaving 1/4" or so on the sides.
- When you drywall, leave the opening the size of the inside of this framed area you just made. The A/C unit will just slide into this window. You will stuff foam into the gaps after it is in place to prevent light leaks.
- On the back of the air conditioner, at the bottom, there is almost always a condensation drain, unless this is outside, you will want to run a hose from this hole to the outside. During the summer I had a considerable amount of water drip all over the garage before I realized it was happening.
Comments
I stole this comment from a thread on photo.net, I hope Terry doesn't mind.The easy answer is to buy a darkroom fan and darkroom vents. These are manufactured devices that are light proof and have a fan or not. I would be careful venting into a crawl space. I would run a duct from the exhaust to the outside. For 880 cf, you want a fan of between 88 and 220 cfm. That will give you between 6 and 15 air changes per hour. Remember to take into account that ducting will reduce the air flow of the fan due to backpressure (technically static pressure losses). The best setup for a darkroom is a combination of positive and negative pressure ventilation. You blow filtered air into the darkroom and you power exhaust air at the same time. You size the fans such that you blow in slightly more air than the draw out. This way any leaks leak air out of the darkroom, rather than in carrying dust. THe best place to exhaust is over the sink. This way the chemical vapors and dusts are removed closest to the source. The absolute best way is via a slot hood. This is an opening about 1-2 inches high the width of the sink. This is the exhaust port. You then size the exhaust fan to suck about 200-400 cfm throught the slot. Antyhing from the sink rises slightly and then back and out the exhaust. I built this for my sink and it works great. BTW my background includes industrial ventilation design for contaminant control. So I am giving you advice to make a GREAT setup. The other posts will work, maybe not as well, but they will work. The big thing is to exhaust near the source and get enough airflow. -- Terry Carraway, September 01, 2000.
Visitor Comments
The comments stated below are not necessarily the opinions of Andy Hughes or DarkroomSourceWhen planning the ventilation system in conjunction with the air conditioner, the builder may want to make sure that the conditioner does not simply recirculate the air already in the room. If this is the case, you may want to add a positive pressure fan (filtered, of course)in addition to the exhaust fan and AC unit.Contributed by on 2000-07-09 00:00:00
I am a young photographer, so i\'m too poor to own my own darkroom (not yet buttt soon!) but to the story my teacher used one of those \'ionic breeze\' air cleaners this year and that cut the duts way down compared to last i can really see an improvement in my prints . i recomend the big one with the anti-germ light sucks that bad boy sucks up all the dust from the ceramics class next door like a champ and even kills of the germs from those dirty freshmen.Contributed by on 2005-01-20 21:27:43
