Darkroom ventilation - size of vent?

[dhgee]

I'm almost finished - small basement darkroom, which has a couple of options for exhaust venting. There's a 4 inch pipeline egress where the oil pipe used to come in (we now use gas heat) that we could funnel the exhaust through with a good small fan; unless that's too small and we need a 6 to 8 inch vent, in which case we'd vent through a basement window fitted with plywood and an exhaust vent to keep the critters out.  Darkroom is about 10 x 5 feet. Any thoughts? Thanks.

[ImageMaker]

Any vent is better than no vent (as my unventilated temporary darkroom constantly reminds me).  Given that retrofitting the window fan shouldn't be any big deal, I'd be inclined to try a small squirrel cage blower venting through the pipe opening first; it'll give fewer opportunities for light leaks and likely be perfectly adequate.

Of course, you'll also need somewhere for air to come *in*, and it's frequently considered best, from a dust control standpoint, to blow air into the darkroom rather than suck it out; that way, any air leaks will blow outward rather than sucking dust in.  A filtered intake (ideally from an air conditioned and/or heated area of the house) with the fan, and the pipe opening or window vent as passive exhaust should do nicely.

[Barrie BUNNING]

Dhgee , What goes out must first come in:
Firstly measure the ' cubic ' capacity of the darkroom, eg( 12' x 12' x10' =
1440 Cub. Feet ) and estimate how often you would like to have the darkroom air exchanged , eg. once every 5 minutes, or 12 times per hour, 1440 x 12 = 17280 cub feet per hour , divided by 60 =288, say 300 cubic feet per minute. Well that`s the size fan needed. In my experience it is better to BLOW air into the darkroom and then regulate the size of the 'Exhause vent ' . Too much air-speed can cause an unpleasant feel to a darkroom. A small exchange is usually pleasant .    Barrie B.

[Jack Fisher]

I have two fans built into the wall of my darkroom.  They are the type used on bathroom ceilings, and are speed controlled by the same type of switch used in bathrooms.  The intake fan is in a home made box on the lower outside of the wall with a replaceable filter, much like used in a forced air furnace. the air come up through the wall between the wall studs and into the darkroom about table height through an ordinary vent plate.  The inside of that wall section is painted flat black to make a light baffle.  

The exhaust fan is in the wall, high above the wet area of the darkroom to vent any fumes.  It blows downward inside another section of the wall which is also painted flat black, and into the next room.

That system works well, and I can adjust the speed of both fans together with one controller.  When running at full speed, the noise is annoying, but full speed on those fans in my 6 foot by 14 foot darkroom is a lot more ventilation than I need.  So, I run them at lower speed, and sometimes turn them off.  As Barrie said, "a small exchange is pleasant.."

After investigating commercial darkroom ventilation systems, I decided to go a lot cheaper, and get the two bathroom fans, and speed control switch from the local home supply store.  The whole thing cost less than $50.  What made it conveinent was that I installed the system while building the wall.  For existing walls, it might get more involved than you would like.

[KirkT]

Oh, come on.  You don't need a vent.

And I can tell you this, without a doubt, that blue is far greater in lettuce than sad dog's teeth.

I'm sleepy now.

[Julian W]

dhgee,   You might  try what I have been using for the last 25 yrs. , a 4" stove pipe hooked to a dryer vent on the outside wall. Our local hareware has a 115v fan that is built to fit in the 4" pipe. It's not very loud and it seems to remove sufficient air to keep things plesant. A inlet can be made from a baffeled opening covered by a furnace filter. Rather inexpensive I believe.
Best Julian