Darkroom ductwork/ventilation/plumbing

[BetterSense]

In my house I have an 8x10 foot closet that I want to darkroomify. It buts directly up to a bathroom. On the other side of the wall from this closet, there is a bathroom with a shower/tub combo installed (with tile) directly on the other side of the wall from the closet. If I wanted to get real destructive, I could just tear that wall out and combine the closet and bathroom into a darkroom, but that approach lacks WAF.

The problem with the closet is there is no ducting into it, no plumbing, and no ventilation. The bathroom, on the other hand, has a duct in the ceiling and also has an exhaust fan in the ceiling.

My plan is to put a "T" into the ductwork going into the bathroom ceiling A/C duct, and run that it into the closet ceiling. This will cut the air going to each by 1/2, but I can have adjustable ceiling vents to close one room or the other off room off.

Then I will install a bathroom exhaust fan in the ceiling of the closet and "T" that into the same vent the bathroom exhaust fan goes too. The bathroom ceiling fans I have looked at all have 1-way valves installed in them so this should be enough to prevent crossover (no point in venting the darkroom fumes into the bathroom or vice versa).

For plumbing, I suppose if I cut a hole in the drywall in the proximity of faucet-side of the tub/shower combo that is installed on the other side of the wall, I will be able to see the plumbing and tap into both the drain and the hot/cold lines for my darkroom sink.

I'm not a plumber, HVAC person, or electrician, but those are my thoughts. Do you think it's worth approaching?

[Henry Ambrose]

Sounds like a good plan in general. The size will be very nice for a "big enough" darkroom - just about perfect for one person. Put a 24-30" deep 10 foot sink on one wall and 10 foot counter for enlargers on the other, leaving about 3 1/2 to 4 feet in the middle to walk in. Makes a very efficient space.

[WayneStevenson]

Your first plan would be to verify where your fans are bringing the air. Not all bathroom vents actually vent to the outside. Poor workmanship may have left them venting into walls, ceilings, attics, etc. Which may be fine for humidity (maybe), but not for chemical exhaust.

There is no way to ensure duct work is air-tight without you having seen it, or havng been the one who installed it. No easy verifying that the air you're exhausting into it, is all coming out at the end. And no way to ensure the added air pressure of another fan pushing throuh it isn't going to cause disconnects. Most ducts I have seen are just mashed together without any tape or anything.

Aim for 6 air changes per hour, or 1 air change per 10 minutes. This is Kodak's recommendation for their B&W chemicals. GOOD bathroom fans will give you 70 - 90CFM. So a good one should take care of your room size no problem.

But also remember that technically, if you're exhausting 80CFM of air, you need to really be bring in 80CFM of fresh air to replace it.....

But also ask yourself how anal you are about your health. If you're not worried, don't take it so seriously. If you are, do it right. Then you have absolultely no worries.

[WayneStevenson]

And you should be pretty spot on with your thoughts of the plumbing. Nothing to it really. If you're not farmiliar with plumbing, as long as you can sucessfully turn off water into your house, you'll be fine as the worst that can happen, is leaky plumbing.

Likely you have copper plumbed so you'll need to solder with a torch. Ensure you use pluming solder (lead-free). You can get compression fittings which make things easier for you, but solder and copper really is the way to go. Unless you go PEX. But the costs raise quite a bit going that route. And you have to marry the copper into the PEX. And if you're renting the crimper, you have to make sure everything is nice and dry before returning it because problems always happen after everything has closed down.

Drain is a little more complicated. Could be a P trap on there. Though might be below where you can see / have access to. Could be encased in concrete. So many different ways it could have done. Most I doubt woud not be worth the trouble.

I bring my water into and out of my darkroom with large kitty litter pails. Also have a water cooler / heater I use when I need a good supply. Been thinking about plumbing a bottle for it so it's a constant supply. But the more I use, the more I have to bring out. Toyed with the idea of using a water pump to bring it out of my darkroom, but not really worth the effort.

[John Jarosz]

Think about resale of the house. I'm sure you'll want to take the darkroom with you when you leave. Construct the plumbing so that you can valve off the water feed, unscrew the drain connection and replace it with a cap. It would help if the means for disconnecting or valving is inside the wall so you can just put drywall or some kind of panel over the hole to cover it.

It sounds like you've thought this thru OK.

john

[BetterSense]

I figured I would install a 14x14 plumbing access panel in the wall (under the proposed sink) and simply leave the cover off of it while my sink is installed. When I remove the sink, I should be able to cap the pipes and just put the acesss panel cover on.

I think the hot/cold water shouldn't be a problem but I don't know what tub drains look like so I might have some surprises; the bathroom is on the second story and the tub drain could be too down close to the subfloor to tap into easily.

Speaking of resale value, if I put in a big darkroom sink, don't I need some kind of backsplash guard? Otherwise the back would just be drywall.

[Colin Graham]

I did something very similar to a spare bedroom that shared the plumbing wall with a bathroom. Pulled water from the tub and connected the waste line under the house, past the tub's p-trap.

You will also need a vent to let the sink drain properly- that might be difficult to tap into an existing one, but if running a new one out through the roof is impractical, you can use a studor vent that attaches to the waste line after the sink's p-trap with a t-fitting.

Panasonic makes excellent bath fans. The whisper green line are very quiet and efficient- you can run them all day and not get noise fatigue. That's good advice about checking the ducting- better to add a new dedicated duct, too many bends reduce the CFM dramatically, and it's true most houses just have the ends of the exhaust ducts laying in the attic insulation or jammed into a bird block. Also, most bath fan dampers don't seal very well, so with the pressure differential you might force exhaust odors into any areas that share the same ductwork. A darkroom can add a lot of moisture vapor to a modern supertight house, so the bath fan is as much for air moisture control as exhausting odors, or mold can become a problem quickly.

I used a sheet of thin plywood laminated with formica for a backsplash, screwing the top of it to wall studs and caulking the bottom to the sink. Should be easy to remove without too much damage, just putty a few screw holes.

[Henry Ambrose]

You can install vents in the wall to let air flow through. Use the stud cavity as a duct -- one "return air" grill goes at the top of the wall opening to one side and the other at the bottom opening to the other room. Or put a dark vent straight through the wall. Either is easy to fix if you move by replacing with a piece of drywall. This might be better later on than a dark vent through a door. Drywall is cheaper and easier to fix.

I'd consider a new fan and vent for the darkroom as others have suggested. Place the air intake above the sink and away from the source of incoming air. What you want is clean air coming from behind/beside you and replacing the dirty air that's being pulled off the sink. Clean air flowing past you.

And as long as we're being critical of venting practices, you don't want either the bath or darkroom vent emptying into your attic. Not even if code allows. Vent through the roof and outdoors. Down side there is another piercing of the roof but better overall if done right.

[BetterSense]

Well there is already a through-the-roof stack from the bathroom vent; I figured I would "T" into that vent in the attic and share the through-roof pipe. It's unlikely I would need to run both the bathroom vent fan and the darkroom vent fan at the same time.

[Drew Wiley]

Best to position the fan duct where it pulls the air from the back of the sink, or up from
that area, rather than across your face. If your exhaust fan will accept a variable speed control that is very useful, so you can adjust the air as needed. 80cfm is a bare
minimum - if it is rainy or humid outside, you need something which will push against
to hydrostatic pressure, and the more kinks and corrugations you have in the ductwork, the more air friction will be involved too. Make-up air is essential, so you'll
also need a light-tight air intake. For drains etc be sure to use plastic pipe like ABS,
since metal connections can be corroded by many darkroom chem.