Is there any need for a darkroom window?

[J Rollinger]

I'm planning a small darkroom in my basement and was wondering if a window is necessary? There is a glass block window in the area now that i would rather permanently seal off. I plan on installing a vent to remove the moisture from the room but was concerned about bringing fresh air in. Would i be fine with just the vent?

Thanks
Jim

 

[DLawson]

I plan on installing a vent to remove the moisture from the room but was concerned about bringing fresh air in.

If the vent has a fan, then you are bringing fresh (indoor) air in anyway.

The fan pumps air out, leaving a slightly lower pressure in the darkroom. Then new air leaks in wherever it can (gap under door, etc.).

There are various camps on this. A fan blowing out gives what is known as a negative pressure situation. A fan blowing in (with a passive vent out) gives a positive pressure situation.

There are lots of fans (no pun intended) of positive pressure. You know where the air come in, so you can filter dust there. It is said that positive pressure gives less dust settling on things, but I've never understood that one.

As for your lungs, both are probably identical.

 

[Diapositivo]

I have no experience of forced ventilation but I would reason that if you adopt negative pressure, you expel air of your darkroom and all the bad smells of chemicals, and you have air from the rest of your house leaking in, which may have dust, but does not smell.

If you adopt a positive pressure situation, you get fresh air from outside, and you can filter it from dust, but you will push smell of chemistry in the rest of your house. So if you have other rooms in your basement, that you use for your everyday life, I would think twice before adopting positive pressure.

The best solution is probably as it is done in offices, forced ventilation in, forced ventilation out, you can choose between slight positive pressure and slight negative pressure, but the double fan solution should be superior in any case. You could install a duct that brings air deep inside your room, and a vent to expel it from a peripheral wall.

Fabrizio

 

[JBrunner]

I power a vent to the outside, so I have a negative pressure darkroom, but I have an intake from the house that I filter. Having the filter on the intake means the fan blows unobstructed to the outside, moving the most amount of air. This has worked well to leave dust out and send smell out, so two vents. I'm sure there are "leaks", but they are negligible compared to the air I'm moving through the darkroom from inside to outside. The intake to the vent that blows outside is located a foot above and a foot behind behind the sink, that way it doesn't draw fumes from the trays over my head, but back and away from me on their way out.

 

[eclarke]

You also don't have a lot of control on moisture, uneven vapor pressure will equalize itself on both sides od a 6 foot concrete wall! My neighbor took his glass block window out and replaced it with a 3 fan panel when he built his darkroom, it seems nice to be able to turn the air over in the basement once in a while. I use an Airpura 2000 sq ft/hr air purifier with a hepa filter to scrub the chemicals and keep dust down....EC

 

[Steve Smith]

It is said that positive pressure gives less dust settling on things, but I've never understood that one.

We have clean rooms at work which have positive pressure. I don't think the actual pressure will affect dust settling on things but every time you open a door from a positive pressure room, air goes out. If it was a negative pressure room air would come in and probably bring dust with it.

If you positively pressurise a room you can filter the air and have complete control over what comes in.


Steve.

 

[c.d.ewen]

Anyone who creates a negative pressure situation should make sure there are no gas/oil-fired furnaces or water heaters in the affected area. If you expell air, it gets replaced from somewhere, and you don't want that somewhere to be from the carbon monoxide laden exhaust of a heater.

Charley

 

[bblhed]

The reason people are big on Positive ventilation is because if you use use positive ventilation you have better control of the amount of dust in the air because you can filter the air coming into the space more easily. With Negative pressure you get more dust because you are sucking in air through every dusty crack that will let air in. Negative pressure has the added advantage of venting all the fumes to a single location, not out all the cracks in the room.

Negative pressure is good in your bathroom where you are trying to remove moisture but don't care about dust.

Positive pressure is good in a paint booth where you want to limit particulate (dust) in the air. Then again people in paint booths wear an outside air respirator.

The Darkroom is a double edge sword, you want positive pressure to keep dust out, but you want negative pressure to be able to evacuate chemical fumes quickly.

You will have to decide, but now you know the advantages of both.

 

[sepiareverb]

I love my darkroom window. Where I live I can work on moonless summer nights with the window open. Few printing sessions can compare to the pleasure of working with the windows open and a nice summer breeze blowing through the darkroom.

 

[Steve Smith]

Anyone who creates a negative pressure situation should make sure there are no gas/oil-fired furnaces or water heaters in the affected area. If you expell air, it gets replaced from somewhere, and you don't want that somewhere to be from the carbon monoxide laden exhaust of a heater.

Do you still have oil or gas appliances which draw air from the room?

In the UK they are all either fan assisted or balanced flue and draw the air in from the outside. The flues are one tube inside another with hot exhaust going out through the inner tube and fresh air replacing it through the outer tube.


Steve.

 

[Diapositivo]

Do you still have oil or gas appliances which draw air from the room?

In the UK they are all either fan assisted or balanced flue and draw the air in from the outside. The flues are one tube inside another with hot exhaust going out through the inner tube and fresh air replacing it through the outer tube.

Steve.

Somebody might still have a traditional fireplace, or stove, in their basement. Normally nowadays one would install a fireplace with an air intake in an external wall of the same room, so that the depression caused by the chimney is immediately compensated by the inflow of outside air at atmospheric pressure.

In this situation if you insert a fan in an adjacent darkroom to expel air outside I think you are in danger because the opening in the wall of the fireplace room might not completely "decouple" the two rooms, and if the fan is sufficiently strong it might attract air both from the opening in the wall AND from the chimney.

In this case, if I get it right, to be safe one should open an air intake in the darkroom as well, so as to decouple it completely from the adjacent rooms.

Fabrizio

 

[fschifano]

Anyone who creates a negative pressure situation should make sure there are no gas/oil-fired furnaces or water heaters in the affected area. If you expell air, it gets replaced from somewhere, and you don't want that somewhere to be from the carbon monoxide laden exhaust of a heater.

Charley

So, with a positive pressure ventilation system, the air has to come from somewhere. In a basement, it might not be from the outside. It could be from inside where there are heaters, furnaces, etc. If you have a CO problem, the least of your worries is the darkroom.

 

[squinonescolon]

+1 to a window. If you plan it well you can print while looking outside, I do. My darkroom window looks out to the garden and it's specially lovely in the afternoons when the light is raking and the wind from the SF bay blows in. It's a pleasure printing like that. I ordered red film form a company (I can't quite remember the name right now) and it works great. I do use a meter to get my work print. Shades have to be drawn while I measure, but once the first work-print is done, the shades come down, and the rest of the session is done while looking outside.
Steven

 

[Maris]

I insist on an emergency exit and a window will do. It goes back to my career as an analytical chemist where a fire or chemical spill near the only door out meant doom. My worst incident was the rupture of a 5 litre plastic bottle of glacial acetic acid, stop-bath concentrate, that had become embrittled in long storage. Leaving via the window was a blessing although going back in with a bag of soda-ash to neutralise the mess wasn't.

 

[J Rollinger]

Thanks for all the detailed advice. I'm going with the window, i just have to make sure its light tight.