I finally picked up a 400 watt hps today. The reflector is a sun system that has 4" ports for ducting. Will one of the 4" inline duct fans from lowes or home depot be enough to keep it cool in a 3'x4'x5' cabinet? I plan on sucking hot air from the top of the cabinet through the reflector and out. I would like to buy this asap if it will work. What do you guys think? does anyone use them on their lights? how loud are they? I have a 5" 110v computer fan I was going to use but its very loud.

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i have several of those fans from home depot, also 4" and they work good. i just bpought a power tool replacement cord with the ground on it and wired her up. If it's quite in your house you might hear a little humming from the fan but other than that its fairly quite.

I ended up going with the 6" 250 cfm one although I dont think it really moves 250cfm. It is fairly quiet. I am warming up the light now. As long as the temp stays below 85 degrees I will be happy.

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nice man im gonna be using those inline fans aswell

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these fans cannot move large volumes of air and restricted they move less than half of what they claim....

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After running the light for a few hours I agree. At 96 degrees I shut off the light. there is no way that the fan even runs at 100 cfm let alone 250cfm. lt looks like I will be reconfiguring my duct work tomorrow. I am going to have the air cooled light sucking cold fresh air out side the cabinet and the passing it over the light and out I am going to have to setup a separate exhaust fan for the cab. I was hoping to do it all with one fan but it looks like thats just not going to work. I have 3 passive intakes on the back wall so all I need to do is add another fan and have it blow through a scrubber out side of the cabinet.

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Anything I say is fictional or theoretical. All pics posted by me are stolen from the web or are very good fakes.