Hood Builders, lend me your ears

[SkiFletch]

So as some of you know, I'm building a hood for my tank and am looking for some oppinions on fans. The framing of the hood is allready cut and the inside stained white. Next step is to notch out my overflows in the back and notch out some holes with the jig saw. I've designed the hood with a lot of room for fans since its 12" tall. I was thinking some 120mm A/C fans (since I'll have plenty of A/C wiring for the lights). But how many should I put in there? I was leaning towards having two pushing air into the hood and two interior pointed at my water level for extra evap cooling. Exhaust would happen through the extra room created by notching out the overflows. What do you guys think of that?

[JackiinFl]

I would think if you put 2 fans sucking cool air in then none pushing it back out you will have warm air blowing at your water, heating it.Even with some holes notched for the overflows thats not much of an escape. IMO the best thing to do is put 2 or even 1 fan blowing in and 2 or 1 fan blowing out keeping the bulbs and canopy cool expecially if it's wood, when the wood gets too heated it cracks. The bulbs also don't last as long when they are kept warm. If you want to cool the water through evaporation why not add a clip fan to your sump? This is just a thought
Good luck

[Chrsnwk]

What my way of doing things in hoods i've constructed, is to have 2 fans, each in a short side of the hood, both blowing air inwards, and 150-300% of the intake area cut into the top of the hood above the lighting covered with louvered soffit vents. (example, if i cut 2 holes for 3" fans, i would have 3-5 3" holes in the top of the hood, or an egress equivilant in area of some other geometry) IME this encourages the heat already produced by the lighting to leave out the top, which is where it naturally wants to accumulate anyway.

My hood fans of choice are 120V muffin fans froma Digi-key catalog, chosen sized to turn over the volume of the hood 5-10x per minute and since i hate noise, the lowest Db rating i could find.

On my AGA 29 reef witha 175W MH bulb I had used 2 Sunon fans Part number 1083HBL which drew .13A each.

As for fans blowing at the water, I have one blowing onto the "waterfall" in my sump, but that is just a cheapo clip on desk fan.

[SkiFletch]

Thanks for the oppinions guys. Cutting through the roof will probably not be an option since I need most of that space for my lighting. Since the tank is a 45, its only ~12" wide which leaves me just enough room for a Halide and a PC and not much room for fans. I'm pretty much limited to the sides or back. Right now I'm leanin towards two on the sides blowing in, and one in the back blowin out, along with the larger holes by my overflow box. Should have a mostly positive pressure inside the hood this way.

Chris, thanks for the tip from digikey. Never thought of ordering fans from them :)

[Rwojick]

I have started the same project and I am going to be routing some holes in the top to allow some heat to escape alog with a few fans in the back for real ventilation, the slits don't interfere with the reflectors and alow heat to escape.
Rob

[Chrsnwk]

Another reason I've had for no fans actively exhausting the hot air is an issue of fan longevity. If the air they are moving is from the outside, it's (relatively speaking) dry air, as opposed to warm moist salty air that will corrode the bejesus out of the bearings, shafts, grilles, blades, etc. If I put a stainless screen on the outside of the fan to filter dust and other such things, (also from digikey) the fans remain quiet and virtually maintainence free for years.