Canopy Fan Sizes

[lilredwuck]

I have ripped apart and old computer and took the on off switch, the processor fan, and the exhaust fan. One is 60mm and one is 80mm. I just built my new canopy. It is 18" tall, 2 doors in the front. Sides and top are sealed. The back has two 1x4 lengths downward on the back. 7" down in back is covered leaving a 9" gap in back. What fans should I use. Thinking I want some thermal sensor fans or are they just attachments for a fan? Anyway I have a 60 and 80mm fan. I plan on cooling metal halides 2 175w bulbs, 90 gallon tank. Should I cut into the side of the canopy or just mount them in the open space in the back or cut into the back to add them. The lights will be 6" above the water, canopy is 18" so I am going to suspend it from the top with some chains that come in Walmart shop lights I have laying around. Should I get the thermal sensor fans? Is that all I would need or do i need some kind of controller as well, I think I say just a sensor that hooked to a fan but can't remember

 

[gio28]

i found that cutting out holes on the top of the canopy to suck the hot air out works well. the hot air rises to its efficient to suck the air out of the top. also install fans on the inside if you wish to cool the bulbs. i dont cool mine and its fine...the fans sucking out the hot air from the top suffice.

 

[scsinet]

I'm not a big fan of blowing air directly on the lamps. Halides are designed to run hot, I've always been leery of negative consequences of doing so.
Thermal sensor fans have the benefit of running only as fast (and therefore as loud) as is necessary to keep the canopy cool. One thing to keep in mind is that thermal sensor fans are usually calibrated with the intention of keeping electronics like computers cool, so they spin up at lower speeds than you might expect to find in a halide lit canopy. In the end, they may end up running fast more of the time than you might expect. I used thermal sensor fans in a canopy once, and they ran at nearly top speed most of the time, so it might not be worth the investment.
From a size perspective, IMO most hobbyists put in far more fans than are actually needed. All you really need is enough circulation to exchange the air in the canopy a couple times per minute, which most fans are more than capable of doing. I'd say that (2) of either size fan is plenty.
Putting them on the top venting upwards is probably the best plan. The heat will rise to the top of the canopy, so exhausting from there would probably be quite efficient.

 

[flower]

I purchased 4' ice cap fans with the heat sensors..one pushes air in, and one pulles air out...but they are expensive and when running on high, very loud. Folks on this site use computer fans all the time...mine are sold for use in a canopy, so I trusted it more.

 

[gill again68]

Its my understanding that anytime you put a fan in the pull mode it will draw saltwater through it and then its only a matter of time before that fan fails. I would think that if you have holes in the top of the canopy and are pushing air into the canopy that would provide, combined with the natural tendency of heat to rise, enough flow to carry the air up and out.
Keep in mind I dont know as I am still setting up my display but this all makes since to me.