80mm case fan to cool MH?

[Mykayel]

I ordered a 175 MH retro kit and I'm thinking about my hood design. Concerning cooling, I'm planning on using two computer case fans for cooling (one in, one out). Would you suggest using 80mm fans (35 CFM) or 120mm fans (100 CFM). I know the bigger fans would provide better cooling, but 120mm (4.75") fan just seems huge and not to mention they are noiser (38 dB vs. 25 dB).

what do you use/suggest?

 

[chadfarmer]

two computer case fans for cooling (one in, one out).

both in or both out they dont work aginst each other

either fan will work and get ready to top off the tank more

 

[kentrob11]

mount both blowing in and then leave a 1" wide vent running the length of the top of your canopy for the hot air to escape....I ran a 90 gallon with dual 400watters on HQI and never had any problems with that fan configuration....

 

[Mykayel]

I guess i should have explained better. I still plan on having an open top, my "canopy" will just house the MH fixture and hold it 10" above the water. I plan on covering the bottom with a piece of glass to protect from any splashes so the fixture would be completely enclosed, and hense the need for fans as I assume it would be worse than an oven in there without cooling. So all I am trying to keep cool is the MH bulb. I plan on mounting the ballast outside the encloseure but still within or on top of the "canopy".