reversing darkroom fan

I just installed a new Doran 12x12" darkroom fan. The problem is the fan is blowing into the darkroom instead of exhausting. Does anyone know how to make the fan run in the opposite direction. I installed one just like it a few months ago and it works fine. I tried to reverse the hot wires but it still runs bass ackwards. I thought that maybe that would reverse the polarity. HELP! ......Thanks in advance, Robert

I guess just mount it on the other side of the wall?

Jon

Robert -

I'm not familiar with the Doran fan, but the simple answer is to simply flip the fan to its other side.

The fan I use has an arrow embossed in the metal frame to indicate the both the direction of rotation and the direction of air flow.

On the other hand, the ideal darkroom ventillation system is "positive pressure" which means that air is forced into the darkroom. If you use a fan to pull air out of the darkroom, it will find all kinds of paths to flow in - around receptacles and plumbing pipes, around doors, etc - pulling dust in with it. But if you force air in, and include a filter in the air path, then those "spurious" paths will become the ways that air leaves. In that arrangement, you have much better control over dust.

I contacted the Doran Co. They are sending a new motor and fan blade today. If I had to wait to exchange it with B&H it would have been weeks. Kudos to Doran's customer service.

Thanks Louie. I already have a filtered fresh air supply into the darkroom. It is the toxic fumes I'm trying to exhaust at this point.

Does anyone use both a fan for incoming air and a fan for exhaust?

If your intention is to eliminate odors then mounting to the other side of the wall as previously advised is good. If your desire is to achieve good ventilation than I would suggest a more complex solution. Build an air tight plenum on the outside of the wall your fan is mounted to which holds a couple of auto air cleaner filters. Install a pipe from the opposite side of the darkroom that leads back to the plenum. Then connect the fan to a voltage reducer, a light dimming switch may work fine, for speed control. Now, you have a recirculating ventilation system with air cleaning.

RobertP said:

I contacted the Doran Co. They are sending a new motor and fan blade today. If I had to wait to exchange it with B&H it would have been weeks. Kudos to Doran's customer service.

Click to expand...

Well the doran fan arrived and I replaced it. Same thing...the fan blows into the darkroom instead of exhausting. So I took the fan blade off and reversed it. This is a small aluminum fan blade with a boss welded to the center with a set screw to hold the fan to the motor shaft. Apparently with this run of fan blades they must have welded the boss on the wrong side of the fan. I turned the fan blade around and it works like it should now. This puts the fan a little closer to the motor but with some creative bending it works like a charm. Now I have a spare motor in case one should burn out. Problem solved. Robert

jstraw said:

Does anyone use both a fan for incoming air and a fan for exhaust?

Click to expand...

Yes. The incoming air is sucked by a fan through a high quality furnace filter to keep any dust or dog hair outside the darkroom. This is on the dry side of the 10x13 foot darkroom.

On the opposite wall, the wet side, I have two fans with 4 inch PVC pipe putting the intakes at the top of the eight foot sink splash rail, sucking the fumes from the trays away from me and outside.

I particularly like the Panasonic Whisper Line fans because they are very quiet, a bit more expensive than most and have the added advantage of sending the air in the direction indicated.

John Powers

jp80874 said:

Yes. The incoming air is sucked by a fan through a high quality furnace filter to keep any dust or dog hair outside the darkroom. This is on the dry side of the 10x13 foot darkroom.

On the opposite wall, the wet side, I have two fans with 4 inch PVC pipe putting the intakes at the top of the eight foot sink splash rail, sucking the fumes from the trays away from me and outside.

I particularly like the Panasonic Whisper Line fans because they are very quiet, a bit more expensive than most and have the added advantage of sending the air in the direction indicated.

John Powers

Click to expand...

I would LOVE to see a photo of this arrangement at the back of your sink? What kind of fans are you using to connect to the 4 inch PVC? Where does it vent to...outside? Very interested in this arrangement and timing couldn't be better.

wilsonneal said:

I would LOVE to see a photo of this arrangement at the back of your sink? What kind of fans are you using to connect to the 4 inch PVC? Where does it vent to...outside? Very interested in this arrangement and timing couldn't be better.

Click to expand...

I am sorry but I don’t have a digital camera to show you. Possibly a description will help. On the outside wall of the basement darkroom I have an eight foot stainless Arkay sink on a stand. There is a cabinet to the left of the sink holding the print washers. That pretty much fills the 13 foot wall.

Above the sink in the rafters approximately four feet apart are two in line rafter fans pointing outside. The top of the wall is about four feet above outside ground level. The 120 cfm Panasonic fans are here http://www.rewci.com/panwhisvenfa.html. The intake for the fans are about two feet in from the wall. White 4 inch PVC pipe from Lowes or Home Depot is connected to the fan intake. PVC pipe drops and curves down to the splash rail of the sink back. At the sink end of the pipe I have two Ts effectively giving intake the 8’ length of the sink. The sink is 30” deep. I use stainless trays for 16x20 prints. The intake is above the trays hard against the far wall and splash rail effectively pulling the fumes away from me, up and out. This as opposed to the common mistake of a having a ceiling fan that pulls the fumes straight up from the trays right by the user’s nose.

Across the 10’ depth of the room I have this fan http://www.rewci.com/panfvwhis.html pulling air through a furnace filter, out into the darkroom at about four feet, toward my back when standing in front of the sink, toward the intake of the exhaust fans.

Again these fans are more expensive than common bathroom fans, but they are Q U I E T, allow me to listen to music or simply think about what I am doing in silence. Kodak says the minimum accepted is to change the air in the room six times an hour. Personally I like to have enough breeze so that I have to wear heavy shoes and hold on with one hand.

I hope this is clear. If not please ask questions.

John Powers

jp80874 said:

Above the sink in the rafters approximately four feet apart are two in line rafter fans pointing outside...

I hope this is clear. If not please ask questions.

John Powers

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Yes, John. Thanks, that's very clear. Gives me some thoughts on different ways to rig my exhaust system. Thanks,
Neal

I built a s/s backsplash for my sink that is shaped like a 10x10-inch x 9-foot (length of my sink) 3-sided box. This is set to overlap the back side of the sink by 1 inch, to allow a 1-inch x 9-foot opening over my sink area. Just behind the sink is a 900 cfm exhaust fan on the outside wall, wired to a rheostat, which opens into the backsplash. The backsplash acts as a shroud to collect fumes from the sink area and duct them outside. The backsplash also serves as a flat area to mount the faucets.

Makeup air comes in high on the opposite wall through a fan/filter device used in wood shops. It also has a rheostat to control flow. I usually adjust the incoming flow slightly higher than the outflow, to slightly pressurize the room. Having excess cfm capacity, I can turn it up high to clear the room or for certain processes that create more fumes, and then turn it down to a whisper for other processes.

Awesome looking setup.
N

jp80874 said:

Yes. The incoming air is sucked by a fan through a high quality furnace filter to keep any dust or dog hair outside the darkroom. This is on the dry side of the 10x13 foot darkroom.

On the opposite wall, the wet side, I have two fans with 4 inch PVC pipe putting the intakes at the top of the eight foot sink splash rail, sucking the fumes from the trays away from me and outside.

I particularly like the Panasonic Whisper Line fans because they are very quiet, a bit more expensive than most and have the added advantage of sending the air in the direction indicated.

John Powers

Click to expand...

Thanks very much. I'll take a look at those Panasonic fans.

Doran Fan Disappointing

I went the easy/cheap route on darkroom ventilation. I went with a Doran 12x12 on one end of sink, and at the other end, 6 feet away, is a lite-tite vent. The Doran is advertised as 400CFM. I hooked it all up and it didn't seem to move the air at all, similar to another post here on APUG. I called Regal (nice people) and their suggestion was to remove two of the four internal baffles. I did this, and was able to get some perceptible airflow (used an incense stick to create a little smoke for testing). I have a LITTLE airflow, but nothing like 400CFM.

I am disappointed. And it's too much of a hassle to do anything else right now. I've got this 12x12 hole in the wall if I remove the fan and return it. Arggghh.

Why didn't I do the powerful fan and plenum that was previously recommended? Noise. I checked out one of those squirrel cage fans that pulls a true 465cfm, and they're loud. With half the baffles removed from the Doran it's pretty loud too.

Thanks for letting me vent. Any suggestions are appreciated.

Neal