Hood Fan Questions

[Ugla]

I am getting ready to rebuild my hood to accomodate MH lights. It is made of maple and needs to be raised about another 8-10" My question is about fans. I am considerins putting the fans on the back of the hood with two blowing in over the first light and two blowing out behind the second light. They will be 120mm computer fans (about 5") I would prefer not to have holes on the ends of the hood.

Has anyone tried this? Would it work ok?
Tank is 100 gallon acrylic with two 250 watt mogul sockets with reflectors.
I have attached a drawing of the proposed setup

 

[Kensn]

I did have a fan blowing in over each MH from the back of the hood, and 2 fans exhausting out the front top corners of the hood. When I replaced them I reversed the flow. Now I push in room air from the top corners and exhaust behind the MHs. It cooled the tank down a few degrees not blowing in over the mh's. It was just blowing air over a heat source and the circulating it. Now the cool air enters and takes heat away from the MHs and exaughts it. Not a huge difference, but every little helps. Here is a pic of the hood as I was building it, you can see the 2 fans behind the MHs, the ones in the top were not installed yet.

Ken

 

[pvillalba]

well i`m have one clip fan( about 6" with two velocity) attached to one of the corners of the canopy and is in angle to put some fresh air by one corner and exit the heat by the other corner , my canopy is build to 8" and this is doing fine for me .you can try put the air fans on the top of the canopy to pull out the heat like one extractor or like some light systems (orbital , satelite of current or coralife)

 

[Katchupoy]

Ugla... you can even do all 4 of them blows in air.... just put a vent on the top if you dont want on the sides. Since warm air goes up then this is a good solution. Since you are going to use computer fans... which I also use... you can connect them to one high ampere multi-voltage adaptor... maybe 1 amp is more than enough....

multi-voltage means you can adjust them from 3 volts to 12 volts....

I have two 4 inch fans running on 3 volts on a 250watt MH... why? the reason is you dont have no noise in 3 volts.... then if its not enough then make it 4.5 or 6 or whatever suits you... then the more fan the better... whihc in your case... 4 fans...

good luck...

also about the vent on the top... you can put it on the front part so you will have a complete cross ventilation.

-

 

[bc_slc]

I have a similar setup and have fans on the end. Mine are not mounted behind though. I found that on a previous setup that if the tank is near a wall, then the flow is limited. I have vents cut in the sides and the air blows out. I used to have it blow in, but for my particular tank, it runs cooler with the air pulling out. This may limit the lifespan of the fans, but hell, for like $6 a fan, it isn't a huge deal. The nice thing about the computer fans is that if you want to reverse the flow then you just swap the wire input.

 

[reedman]

be careful having fans blowing on the bulbs. This actually changed the spectrum on my XMs and caused them to put out a high pitched whine. When I moved the fan to blow elsewhere the problem disappeared and the color spectrum returned to normal.

If you put vents on the top of your hood natural cooling will happen as hot air rises. I used the plastic vests designed for the outside of a house to vent the top of my canopy and I have 3 fans blowing air across the surface. just a thought for you to chew on.