fan direction

[Quinn]

well my tank is fluctuating by over five degrees F per day, with two fans in the canopy. they are producing a fair bit of air flow, as the wood in the canopy is only slightly warm, the back of the reflectors are cool enough to touch - however my eurobracing is much hotter that i would have expected, obviously because of the light blazing down on them. i have to add more venting, because if i close the canopy lid and door, the fans actually slow down, as they are pushing more air in than is escaping i expect. so i am going to add two more fans. the question is, should i put them below my other two, meaning i'll have four on one end? should i put them on the other side, blowing out? the easiest thing would be to actually put them blowing down from the canopy lid, and i expect this would cool the eurobracing the most... any opinions?

[Chad]

In my experience in the computer industry, trying to keep high end systems cool, getting the air out as much as in is just as important. So, I would say putting two fans on the opposite end blowing out would be a good option. It is hard to say since I don't know what your vents are like but if you have two fans blowing in and no quick way for the air to escape its just going to swirl around and make it hotter.

Chad

[Jack]

It's best to have an input and output. I use a bigger fan for the input to really force hot air out.

[ree-fready]

you definetly need as much fan cfpm blowing out as in and i would say more. my canopy cooled down by alot. i have 1 fan inside the canopy moving the air around and have 1 sucking it out. air is able to enter the rear of the canopy via a 3" space at the back of the canopy.

[Quinn]

i'm sold. you all have good reasoning. i've heard that fans blowing out erode eventually due to salt, but hey, what's 14 dollars. i'll set it all up tomorrow. i sure hope this works, because my tank is hanging out at 86 degrees.

[Aquattro]

Unless you have a pressurized canopy, the air is getting out just fine. The purpose of having fans is to promote evaporative cooling, not cooling the bulbs or evacuating hot air. Your tank will cool by having air blowing across the top of the water. If you need more, maybe put a small clamp on desk fan over your sump.

[Quinn]

if i block the vents on the canopy, the two fans i have slow down noticeably. they are at least six inches off the water so that may not be optimal. i may also add a sump fan. we'll see.

[Chad]

Originally Posted by reef_raf

Unless you have a pressurized canopy, the air is getting out just fine.

You'd be amazed the problems that can be caused by some backpressure. If the fans are blowing in more than can escape it will cause some issues. Seen it. Maybe it doesn't relate 100% but having hot gas (air) circulating inside a canopy isn't going to cool things down all that much if it has no way to get out efficiently.

Just my two cents...

Chad

[Delphinus]

I myself do one in, one out. It's a small catch-22 because two fans that each produce "X" cfm of air movement will yield you 2x"X" if they are either both in, or both out, but if in series then you only get 1x"X" cfm despite two fans. But nevertheless, the air movement is more controlled (i.e., comes in one side, exits the other). The difference I found with this arrangement seems enough to convince me. If I put my face in the outward facing fan, it's blowing considerably warm air.

But like Brad points out, it's only keeping the bulbs cool, it doesn't do a whole lot to keep the tank itself cool. For that, you really do need a fan blowing downwards onto the water. I have this over my sump though and despite it being an 8" fan it doesn't seem to keep up. All it does is make me have to replace 5g per day of evap loss! I'm wondering if a fan pointing downwards onto the water surface in the hood itself may not be a bad idea. .. I'm not sure yet.

PS. I should mention that in 3 or 4 years of fans in my hoods, I've only ever chucked out one fan, and that was after about 2 or 3 years of continuous use. And it was one of those bargain bucket fans from Princess Auto -- these fans aren't new. So who knows how many hours of runtime it had over it's lifetime. If you buy a brank spanking new fan I would expect you not to have to worry about garbage canning it for quite some time.