Ventilation specs for darkroom

[Tin Can]

Welcome Wizard of OZ

[Drew Wiley]

Thank you. I have a pair of tinsnips you can borrow if needed.

[Jac@stafford.net]

One question concerns how far we need to move the air - is push or pull or a combination of both better and under what circumstances?

[Drew Wiley]

Pulling air is always more efficient than pushing it. An in-line fan somewhere in between, with ducts both directions, is a compromise. But there are also logistical issues. It's fairly easy to locate a high-quality in-line fan in an attic, and it can be set up to service more than one room or duct line. Wall fans have to be shallow to fit inside stud spacings, and sometimes ceiling fans have to too; but these types, if squirrel-cage design, are less expensive than other squirrel-cage options. A more elegant alternative is a weatherized externally-mounted fan or combination of them, which pulls the air as well as isolates noise. More money. I use a large version of one of these, plus a small booster fan connected to a portable fume arm which I can place just above something noxious being mixed, and does not need to be quiet because it's only temporarily used. It's own flexible duct exits into the main fume hood.

[UnaSutherlands]

To be honest, I don't understand anything about air conditioners at all. Of course, I tried to figure it out myself, but each time I only made it worse. Although everything is simple in the drawings. I don't understand why this is so.

[Drew Wiley]

Let me repeat, pulling air is ALWAYS more efficient than pushing it. But sometimes an intermediate in-line fan is the best logistical compromise. But knowing that doesn't mean I always get it right. Last time I crawled into an attic and installed a big in-line fan using a headlamp, I accidentally hooked up the wiring wrong. When I turned it on down below, it was blowing air back down instead of pulling it up! So back to that cramped attic I went, to correct it.

[Scraps]

Let me repeat, pulling air is ALWAYS more efficient than pushing it.

Thanks for bringing up that point. I want to set up ventilation via a portable floor air conditioner since it extracts a significant amount of air as well as cooling and dehumidifying the basement room in summer months. Since pushing air - as in laundry dryers - is inefficient at pushing air to the outside I should try using an in-line fan. It'll make more sense to install it as near as possible to the window since the basement window is 7.5' up the wall and will require extra piping adding more distance than is recommended for these dryers. I'll treat it the way you installed an extraction fan in the attic.