Fan direction question for a DIY hood..

doublezero

doublezero

Member
I am curious... I just finished building a hood(I like to call it a light box) for my 55g, I have two VHO lights in it... I have a 3" box fan, My question is what direction should the fan push the air??? Hot air out or cool air in???? any suggestions and reasons would be helpful...
thanks in advance
#00
 
ohioreef

ohioreef

Member
I really don't think it would matter. If you're drawing the hot air out, then cool air is flowing in at another vent. If you push cool air in, then the hot air will exit the other vent.
Someone correct me if my thinking is wrong.
Mine just happen to push the cool air in because that's just the way it happened to flow when I installed them. I didn't really pay attention to which way it went.
 
ohioreef

ohioreef

Member
Actually if you blow air into the canopy you will keep the fan itself cooler as opposed to drawing the hot air out over the fan. I hadn't thought of that.
 
B

bluedolphi

Guest
You want to blow the air in!? That would defeat the purpose.
You want to draw the hot air out away from the air that is above the tank. Sort of like an electronic appliance. You want to evacuate the hot air.
JMO.
 
ohioreef

ohioreef

Member
Bluedolphi,
as long as you have a vent at the opposite end of the canopy away from the fan, the hot air will be "pushed" out of that vent by the higher pressure inside the hood.
 
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bluedolphi

Guest
I build out a lot of computer cases. We find it much more efficient/safer to evacuate the heat from the enclosures. High end electronics/amplifiers with built in fans also evacuate the heat. In fact we purposfully "reverse" all fans on our power supplies to evacuate rather than blow cool air into a case to create positive pressure. This has always been more beneficial, in fact many manufactures have seen the benefit and are now advertising their power supplies with "reverse" fans (sucking the heat OUT of the enclosure as apposed to blowing air in).
You can put a thermometer inside the hood and try it both ways. I think you will be surprised.
I know it seems like it would be a good idea to blow cool air on an object that is hot and generating heat. But not the case in an enclosed environment. As you evacuate the hot air it is replaced with cooler air from outside the enclosure. The positive pressure idea just has never really outperformed the reverse in my experiences.
JMO.
 
harlequinnut

harlequinnut

Active Member
Ideally, it would be best to have fans on each side of hood with one side blowing air in and the other side drawing air out. JMO
 
bang guy

bang guy

Moderator
If cooler bulbs or cooler water is your goal then blow the air across them. For Saltwater Aquariums forcing air into the canopy works best.
The high humidity, salty air will also start to corrode the fan wiring after just a year or two if you try pulling the air out.
 
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bluedolphi

Guest
Spooky. Oh well. Do what you may.
Do consider that whatever is mixed with the air (including salt), wouild be CONCENTRATED, in a positive pressurized environment. If you want to reduce heat, along with any other matter that would be mixed with the air (smoke, moisture, corrosive salt, for instance), you would want to evacuate, not pressurize, or compress. Compressing (forcing in more air) would concentrate.
A for instance would be a firefighter. They point the fans outside of the building to evacuate smoke, airborne chemicals, etc..
Best way to find out is give it a shot both ways.
 
bang guy

bang guy

Moderator
Who said anything about pressurizing?
If it's easy enough try it both ways. Keep track of the water temp though (hint hint)
 
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bluedolphi

Guest
Bang guy,
You did.
You think it is better to create positive air pressure in an enclosure, by blowing air into it, in an attempt to cool off its contents. I was just trying to explain to you that that is in fact the opposite of what you want to do.
I just realized you are the one who made the post
"The fan will last a lot longer if you blow air into the canopy", sorta pretty much sums things up. Well.... for me anyway.
Yes, be sure to monitor that water temp. That is really the temp we are concerned most about. We just obviously disagree on the best way to reduce the air temp above the tank.
 
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bluedolphi

Guest
It does.... it creates positive pressure. The air pressure inside the canopy will be greater than the air pressure outside. If the fans are blowing in...... instead of out. Not quite like a balloon, more like a leaky balloon.
 
wester97

wester97

Member
just be sure to have a vent on the opposite end of the fan. MY lights came with a built in fan and it blows into the light and across the bulbs and out the other side.
 
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