Fan placement in Canopy

[juiced_rl]

I have seen alot of people place fans on the sides and in the back of their canopies.
I am wondering if I put a 4" fan on the top to draw the heat out if that would be enough.
I am restricted on room in the canopy on the sides and the back.
I am at about 86 degrees with the new MH's and need to get it down. I do not want to cut a hole in the top if it won't work.

 

[birdy]

It will work, but I would blow the air in, studies people have done show that blowing air in will cool a canopy better than pulling air out.
Is the back of your canopy open? if not I would find a way to vent it.

 

[juiced_rl]

It is open but there isn't enough room for a fan because of the reflector for the PC lights.
I am going to try and take a pic in a bit.
I have 2 65watt actinics PC, and two 250 watt MH stuffed in there it's pretty tight.
The reflectors kind of push on each other.
There is probably about 3 inches open air on the back of the canopy.

 

[birdy]

As long as there is some opening in the back for air to move through the canopy, I would mount the fans blowing air in, beause they will displace the hot air in the canopy, the more cool air you have blowing in the more hot air you will push out the back of the canopy.
That is what I would do anyway.

 

[juiced_rl]

Thank you birdy I am going to give it a shot.
I have a few fans laying around that I never used for my car stereo they are actually five inch units and should move a bunch of air.
I am going to place the fan in between the two MH bulbs and hopefully that will do the trick.
If not I am going to have a canopy with a 5" hole in the top for sale and build something much taller.
I am wondering if the HQI MH bulbs put out less heat then the screw in type. Maybe I should have purchased those instead.

 

[birdy]

I think HQI actually put out more heat, at least the ones I do put out more heat than the SE bulbs did.

 

[dogstar]

Im not an Air Engineer but I know hot air rises. So I built my hood totaly inclosed and put 2 fans in the top near the center, either side of the center MH, blowing out and intake vents on each side, down low, near the front.
This lets cool air move constantly in one direction as it gets sucked in down low near the water surface and the fans pull it upwards across the lamps and out. This way the heated air never gets down near the water.
IMO if you blow the air in, It will cause turbulance inside the hood and the hot air can/may get down to the water surface befor moveing out side. JMO

 

[chipmaker]

I have em in the sides on most of my hoods and in the top on a few as well, but one thing I do is make em blow air not pull air out. best to keep any salt laden air from going through the fans themself, as well as the heated air.. I do not think blowing air in actually pushes heat into the water, even if they were mounted above on the top....or if they did the amount would not be enough to notice.....

 

[acrylic51]

I have to agree with Birdy on the fact that I think HQI's do put off more heat than SE bulbs, but have to agree with DogStar about heat rising......I thought along the same lines and when building my fishroom that is why I opted to install a bath exhaust fan in the top of the canopy to pull the hot air from the top of the tank with fans blowing in from the back.......

 

[juiced_rl]

well I was able to get one installed on the top and one on the side.
I do have them both blowing in because after testing them they are pushing a whole lot of cool air.
I turned the MH's on and am watching the temp for a few hours tonight to see how it works.
I will post some pics tomorrow