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I have heard that you should have your canopy fans blowing into the canopy and i have heard you should have your canopy fans blowing out of the canopy. How are they supposed to be?
not sure of "the correct way" but I have one fan at each end of my canopy. One fans blows in and the other fan blows out. I figured this would keep air circulating throught the canopy the best.
I have one at each end of my canopy. They are mounted in a plenum that is about 6 inches above the main top. They both blow out of the canopy. This way the heat from the lights (which naturally will rise) gets sucked up and out of the canopy. I have tried it both ways and this works the best for me.
Well I don't know what the best way is, but I'll tell you how I did it.
On my canopy, I installed two fans. One on the right and one on the left. One blow into the canopy while the other blows out. I also left spaces between the wood on the top of the canopy. This lets convection (rising heat) to take place and remove any heat the fans don't get.
With the kind of heat that is generated from a MH bulb, I would not think that you could get a cold spot. MH will generate much more heat than regular HO or VHO bulbs. I would think you would have to blow "cold" air on a MH to get a cold spot on it. I could be wrong, but I do not attempt to touch my bulbs for at least an hour after they are turned off.
I would blow the air into the canopy and then have vents at the top to vent out the hot air. The fans blowing in will create a slight high pressure area that will also aid in the hot air venting out of the vents.
I don't think "cold spots" like PC or VHO is comparable to halide. But I do know that Metal Halide, sodium, and halogen bulbs must run at a higher temperature to reach optimum output. I don't think there will be any "adverse" effects of fans blowing in on halides, but the idea is to remove the heat that is generated, not cool off the bulb so heat isn't produced. I think you are going to find most proof to be up in the air. Find what works for you and stick with it. Heck, try it both ways and see which reduces temp more, or is quieter, or you like better. For my opinion, however, I'll stick with the "out"