Question about darkroom ventilation

[brian steinberger]

Im building a new darkroom in my house and am not sure about the ventilation. I have a simple bathroom fan that is more than enough for my smallish 11'x11' darkroom. My question is about the louver I will need to install in a wall opposite of the exhaust fan.

Do I need to purchase a special light tight louver such as this? Or is there an easy way to make a simple household louver air tight?

 

[AgX]

You could make a zig-zag air guide yourself. Or a fit a right-angle air duct with long tube, all painted black inside.
Maybe a box-like cap, painted black inside is sufficient.

 

[David Brown]

... is there an easy way to make a simple household louver air tight?

light tight?

The answer is yes, I've done it, similar to what AgX suggests. But at the price of the one you linked to, that seems like less trouble and more chance of success.

 

[M Carter]

The linked louver says it's for 2 different fan models - so it may not interface with the standard ducting sizes for residential fans, something to keep in mind or see if there's a PDF out there somewhere.

There's plenty of ways to go light-tight though, even using flex tubing sprayed black inside and curled around once... or make a black plywood box with in and out on the same side. Honestly, go into a residential bathroom, turn off the lights, and see if anything makes it into the fan photon-wise - I've never seen it, probably in most cases the path the ducting takes ends up blocking the light.

The bigger issue is where does the exhaust actually go? You could just blow it into a well-ventilated attic I suppose, if there's no inspection and permitting going on. Even straight selenium would probably dissipate enough not to worry (yes, flame away on that one folks, and I wouldn't personally do that, who knows how that stuff interacts with insulation, etc.) Getting a proper vent cap installed (so that rain doesn't damage your roof over time) is a DIY job if your roof is DIY friendly. (Mine's about 30 feet up and steep, I freaking hate it up there!!! When we had our roof redone I bought three vent caps and had them installed for future remodeling).

You can also install a wall-mounted vent, that can be much easier. On a brick house, you need to get a hole through the brick (multiple small holes with a masonry drill around the circumference you need, and then smack with a hammer, clean up with a chisel), and you need tapcons to hold the cap to the wall, caulk, and screen - birds love building nests in those things!

If you live in a hot climate and run the AC all summer, humidity can condense on vent piping (which will be cold like a beer bottle) and you can get some serious staining on your ceiling as it drips and pools. You need to wrap exhaust piping/tubing in duct insulation, or spray solid ducting with spray foam.

And when you attach ducting, flex tubing, etc... don't use duct tape!!! It's really not for ducts. Use the silver-foil style HVAC tape (any hardware or big box has it), and also use zip ties to attach flex tubing to solid tubing and mounting flanges (after you tape). Duct tape dries out in a year or so and falls apart, the silver foil is decades-good. Pain in the rear to get the backing off, then you're solid.

 

[brian steinberger]

light tight?

The answer is yes, I've done it, similar to what AgX suggests. But at the price of the one you linked to, that seems like less trouble and more chance of success.

Yes I meant light tight. Haha. Would the 8"x8" louver be big enough for my 11' x 11' darkroom? They also make a 12"x12" model.

 

[brian steinberger]

Thanks so much for the post M Carter! I'm not sure exactly what you mean about the linked louver interfeing with standard duct sizes. I was just going to put it into the wall of the darkroom opposite the exhaust fan to let fresh air in. I will probably use furnace air filter material to filter it. My exhaust fan is a bathroom fan and will be vented just a few feet outside.

 

[mr rusty]

the light trap over my ventilation fan is made of cardboard - I think I used a breakfast cereal box.

 

[Sirius Glass]

A simple bathroom exhaust fan is sufficient in my bathroom-temporarily-converted-into-a-darkroom-and-back.

 

[M Carter]

Thanks so much for the post M Carter! I'm not sure exactly what you mean about the linked louver interfeing with standard duct sizes. I was just going to put it into the wall of the darkroom opposite the exhaust fan to let fresh air in. I will probably use furnace air filter material to filter it. My exhaust fan is a bathroom fan and will be vented just a few feet outside.

I've never seen a darkroom-specific louver like that... I was imagining louvers that are sold for residential exhaust fans, which usually have a round extrusion on the back that metal ducting or flex tubing slides over. That would be a louver that is directly attached to the ventilation system though; if those black louvers are just designed to create a ventilation opening in a wall that's all a moot point of course!

I've got an old house that we've redone several rooms in, and the bathroom fans I've installed are a metal box with a fan motor, where the interior louver attaches to the box itself (the box mounts on the wall or ceiling framing and the louver covers the hole in the drywall). The back of the metal box has a round port that interfaces with standard ducting and on to the exterior louver.

I just purchased one for my darkroom (we've converted a 2-story duplex to one home, so the upstairs kitchen is my darkroom until we can afford to make it into a master bath) so I'll mount it to the ceiling over the trays and exhaust through a roof vent... so I may want some sort of louver to allow air in and equalize the pressure, which perhaps is the sort of louver you linked too?

Here in Dallas, the summer is 90-102°f from may til september, so I'll need to insulate any exhaust ducting that passes through the hot & humid attic... in milder climates that may not be necessary though.

 

[john_s]

I have a small darkroom and use just a small computer type of fan (mains voltage though). It doesn't move a huge amount of air, but it's enough to move the smells out. Fresh air enters through a vent at the other end of the room with simple filter on it. Both vents are just a plywood box, painted black inside, quite adequate as the darkroom is a room inside a room. For outside venting, one extra baffle in the box would be needed.

 

[MattKing]

I could be wrong, but it seems to me that Brian is asking about a louver for an air intake, not the fan assisted exhaust.

It would be really good if you could use the output from an air cleaning unit as your intake, and the bathroom fan for your exhaust.

It would be important to come close to matching the air flow capacities though - with the exhaust air flow being just slightly more than the intake. It would be important to watch humidity as well.

And if you can, use ducting or plastic pipe to extend the intake to the exhaust fan so that odours and fumes from the chemicals are drawn away from you.

 

[Gerald C Koch]

At one time Kodak had a publication on the design of darkrooms. It may still be available used on some sites. It contains recommendations for ventilation. What is important is the exchange rate in ft3/min.

 

[MattKing]

At one time Kodak had a publication on the design of darkrooms. It may still be available used on some sites. It contains recommendations for ventilation. What is important is the exchange rate in ft3/min.

Google "Kodak darkroom design" to find it on Kodak's website (as maintained by Kodak Alaris).

 

[John Koehrer]

A dryer vent or two. One inside the room, one outside. Mounted back to back.

 

[brian steinberger]

Matt you are correct. I'm asking about an air intake. Just a simple vent I can add into the wall to let fresh air in. I was just curious if I needed a light tight one as I linked or if I could use a simple vent and light proof it. Also how to filter it.

Thanks for the responses guys. Good stuff.

 

[brian steinberger]

A dryer vent or two. One inside the room, one outside. Mounted back to back.

But how do you make it light tight? And filter the air?

 

[AgX]

At one time Kodak had a publication on the design of darkrooms. It may still be available used on some sites. It contains recommendations for ventilation. What is important is the exchange rate in ft3/min.

As a guidance is given in Germany a air-exchange of:

8x room-volume /hour


Of course not only the vol/h of the ventilator as such is of importance but also the design of the airstream through the room. Best would be seperate exhausts for critical areas and the for the general rest of the room.

 

[RalphLambrecht]

---

Iended up buildingan airtrap around a simple exhaust.It'spictured inmy book WbM but I don'tapicture of it handy at the moment.Anyway,itworks perfectlyand even blocks direct sunlight shining on it

 

[brian steinberger]

Since you're inquiring about the INCOMING air, I'd recommend that you place a filter in that path. Your darkroom is about the same size of floor area as mine but you don't mention your ceiling height (mine is 9 feet). The fan throughput should be adequate for your room volume. I chose a Doran 10x10 exhaust fan over the sinks vented to outdoors, then installed a Doran 10x10 louver for incoming air on the opposite (interior) wall so as to bring in home-heated air. Inside the darkroom I placed a furnace filter in the interior wall and pressed it against a soft rubber strip around its edges. You could cut this 12x24 filter in half for the installation, so you'd have a spare (it should be replaced periodically anyway). The filter is held in place by a wooden frame on the darkroom wall. It has been successful in minimizing the dust in the darkroom as well. The exhaust fan was connected to a fan speed rheostat control, but I don't use the fan while drying negatives hanging from a cable strung up over the sinks. Never have had a dust problem with the negatives.

Great ideas! Thanks. My ceilings are 7' in the basement. Does it matter which side of the intake I filter? I'd rather filter it on the back side of the wall as so the filter is not seen inside the darkroom and also sticking out from the wall. I guess now I'm just trying to decide which size louver for my darkroom. 8" square or 12" square. And also what placement on the wall? High up? Down low? Can u put it under the enlarger table low on the wall or does it need to be unobstructed?

 

[MattKing]

If you have the intake low on the wall, and the exhaust high, you may get a more complete "refreshing" of the air in the room.

If the filter is outside the intake, it may be less likely to spread dust in the darkroom when you change the filter.

 

[brian steinberger]

Thanks so much guys!! I think I'm gonna go for the larger 12"x12" louver and put it lower on the wall unobstructed. And I will filter on the outside.

 

[M Carter]

The other day I was playing with brushing straight selenium toner on some small scrap lith prints... my quote of the day was "Ggggk - acccckkkk - need to install that damn fan!!!"...

 

[Black Dog]

Sinus is nice and sinus can stop you

The other day I was playing with brushing straight selenium toner on some small scrap lith prints... my quote of the day was "Ggggk - acccckkkk - need to install that damn fan!!!"...

Well at least you won't have any sinus problems for a while

 

[gleaf]

Outlet location.. High or low depends on the fixer you are using i.e. fumes rise or fall depending. Also Kodak mentions that you want to exhaust air under power not pressure supply air in. Reason, so your darkroom ventilation does not push fumes into your home.

 

[brian steinberger]

Outlet location.. High or low depends on the fixer you are using i.e. fumes rise or fall depending. Also Kodak mentions that you want to exhaust air under power not pressure supply air in. Reason, so your darkroom ventilation does not push fumes into your home.

I'm using ilford Hypam fixer.