Northern California here. Darkroom in garage, seems to sit at a constant temperature of 18-22C depending on outside cold and time of day. Usually it's 18C on the dot at night. I typically don't do any heat regulation, I just wear another layer if it drops down a little cooler.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.
To keep dust out the fan should always blow air in to the darkroom - you want positive pressure.
If the inlet air is well filtered the effect of a positive pressure is to blow the dust out of the darkroom along with the excess air.
You need to keep the fan blowing all the time to keep the darkroom dust free. Dust is drawn back into the room if it breathes with changes in temperature and barometric pressure. Counter-acting the breathing doesn't require much positive pressure: a small muffin fan (you can rip one out of an old PC XT power supply) will do the job if the vents are closed. A bit of thin plastic sheet over a hole between inside and outside air can be used as a check that the darkroom is pressurized - make sure it always bulges to the outside air. It is a good idea to check the room stays pressurized in high outdoor wind conditions.
The best filter for the inlet air is one of the 3M or AprilAire fine particle filters.
I keep my house at 60F in the winter. To keep the developer at 68F I use a heating pad under the developer tray. I put ensolite insulating foam between the heating pad and the bench so the pad doesn't waste its effectiveness heating the bench along with the developer.
Last edited by Nicholas Lindan; 07-11-2009 at 10:27 AM. Click to view previous post history.