Ventilation specs for darkroom

[Tin Can]

For anyone interested:
So you will need a low volume fan, perhaps a computer fan will work


(4) There should be at least 10 air changes per hour in the room to ensure removal of
chemical fumes from the area. The supply should be located so that it does not “short
circuit” and feed directly to the exhaust. A darkroom supply of 50% of the exhaust
rate is ideal.

[Pere Casals]

(4) There should be at least 10 air changes per hour in the room to ensure removal of
chemical fumes from the area.

Beyond norms, the key is not to have turbulence. Air has to flow laminar from the emision sources to the extraction, in that way fumes are never breathed. If we have turbulence we always breath some fumes, and we need a lot of air changes to keep fumes concentration low, but it will never be zero. With a properly designed system we breath zero fumes.

A properly designed system is essential when we use some kind of chem.

[Tin Can]

I am out as Pere and Drew tango

Make up air is important and can be very cold or hot depending on location, climate

[Tin Can]

No dancing? It's Hell-O-Ween!

Old threads on DR ventilation found on bottom of current page, some go back 20 years.
https://www.largeformatphotography.i...l=1#post709987

https://www.largeformatphotography.i...l=1#post583499

https://www.largeformatphotography.i...ll=1#post81143

https://www.largeformatphotography.i...ll=1#post30262

https://www.largeformatphotography.i...ll=1#post16335

[Drew Wiley]

A computer fan????? That's like a mouse dueling a mountain lion. Wrong Holiday. This is Halloween, not April Fools Day.

[adelorenzo]

I was reading Tim Rudman's toning book last night and he also recommends a minimum of 10 ACH.

[Tin Can]

OP is trying to figure out DR ventilation for a 6 X 6 X 7ft shed. 252 cubic feet

He needs a small fan, 240 CFM is too big by a factor of 10

I was reading Tim Rudman's toning book last night and he also recommends a minimum of 10 ACH.

[adelorenzo]

OP is trying to figure out DR ventilation for a 6 X 6 X 7ft shed. 252 cubic feet

He needs a small fan, 240 CFM is too big by a factor of 10

I wasn't making any comment on the size of the fan required, I was just giving the OP another data point for recommended air changes per hour.

[Tin Can]

I know you were. I was trying to repeat his needs

All good

I wasn't making any comment on the size of the fan required, I was just giving the OP another data point for recommended air changes per hour.

[Drew Wiley]

You don't know what you're talking about, Tin Man, or I am confusing you with a character in Wizard of Oz? If you take 240CFM, factor in hydrostatic pressure outside on a rainy day, or even in a humid climate, and then air friction from ductwork that cannot be straight because it has to prevent light entering and may very well be corrugated for ease of installation, the real world capacity is about half that air volume at best. Then one always needs a boost factor, even if ordinarily running it at lower volume, in case there's a spill of something you want rapidly exhausted, or during mixing of some concentrated chemical. So a fan of at least 180 cfm is called for, or even better, 240 because there's such an excellent in-line option in that case. That would be the routine specification for even a bathroom that size, where mainly just water vapor is involved, unless the climate is routinely arid. What one doesn't want is a cheap ceiling-mount propeller-style fan that is as noisy as a gas lawn mower.