Fans- Top or side?

jess74

jess74

Member
My new light setup will be here next week and then I'm going to start on my canopy, but I don't know if its better to put the fans on the top or on the sides?
Also, if someone could tell me if you think two 3" fans are enough? My light is going to be 250w MH with 2xVHO's on a 36gal. I would really appreciate any responses to this, as it seems for some reason some people are avoiding my posts.
Thanks :)
 
nas19320

nas19320

Active Member
You may need more than two 3" fans but it will depend on your ambient temp and your canopy design. You may get a lot of different opinions on where to place your fans, some have them blowing out the top and some have them blowing in from the sides. I have mine on the sides blowing air in across the water with an open back canopy.
 
jess74

jess74

Member
Thanks for the reply Nas19320,
Maybe I should have done this as a poll, I'm still not sure which is better; top or sides and I though I could get some opinions of who likes what best. I'll put you down for sides, thanks!
I was planning on having an open back canopy and I just wondered if 3" would be enough because I found a good deal. I originally was going to get the 4" Thermal speed, I guess I should just go with the 4" to be safe.
 
saltynewbie

saltynewbie

Member
wherever you decide to place your fans, make sure that you place them so that they blow air from the outside of the canopy to the inside. this will make your fans last longer. if they are blowing the salty air out of the inside of the canopy, the fans will not last very long at all. just my $0.02! :)
 
buzz

buzz

Active Member
I have 2 - 5 inch fans both blowing in from the top on my 100g. The lighting you have may require more than 3 inch fans to keep them cool. But that depends on your canopy.
I like the top mounted fans for a few reasons. I personally think the canopy looks better, and I like the circulation given by the direction of airflow.
However, both ways work and are used by many. I do agree that having both blow in to the canopy is the way to go. The exhaust will find a way out....
 
golfish

golfish

Active Member
How about running a fan on each end blowing in and one on the top sucking out. You still want to have the back as open as possible.
Better yet, can the canopy and run the tank open top. Its a hec of a lot easier to keep the tank cool.
 
zanemoseley

zanemoseley

Active Member
on my 75 I have a canopy with a 4"x24" opening on the back, on the top of the canopy toward the front I have 4 4" 50cfm fans to suck air in, I could have gone with 2 4" 100cfm fans but 2 of the faster fans I calculated would be quite a bit louder than 4 of the slower fans, the Icecap fans are extremely loud from the specs I have seen, over 50db each
 
jess74

jess74

Member
Hey thanks for all the input!
I was going to order fans from the same site I got my lights, but they were out of them and I didn't want to it to delay my lights too. They had 4" Variable speed fans that were 50-112cfm. So far I've found 3", 3.5", and 4.5". I don't know why but I'm having trouble finding 4".
Keep the suggestions coming; I need to get some of the planning worked out so I can start on my canopy when my lights come next week. :)
 
tonya-sr

tonya-sr

Member
Hey Jess
Sorry, I must have past over your thread earlier. Here's my experience.
I have 4-4" (Radio Shack) fans each at 65 cfm mounted on the top of our canopy. They are tied to the timer that turns on the attinics, our MH's (250w) comes on a half hour later and they're off an hour before the attinics. The house temp is at 76-78 and the tank water is consistant at 78-80. Please note, I hope your canopy is at least 10-12" high. If you are in your tank as much as I am, you will eventually burn yourself:eek: I get so caught up with what I'm doing, I didn't see it coming - I'll remember their presence now

Good Luck I like my MH's and so does my tank creatures.
 
jess74

jess74

Member
Thanks Tonya,
Nice hood by the way! Thank goodness for this site; I've been reading on the DIY and Reef areas about hoods, so I was already planning on making mine around 12" (I'll have to see how it goes). The hardest part is going to be that mine is a bow, but thankfully I have family members that are good with woodworking and can lend a hand if I get stuck. :D I'm kind of leaning toward the idea of having more fans at slower speeds then having large noisy ones. Thanks for the pic, that helps! :)
 
dburr

dburr

Active Member
How about running a fan on each end blowing in and one on the top sucking out.
Actually, did you know that cold air is more dense than warm air? Your fan blade will "grab" and push more cold air than warm. It only make sense to have them all blow in.
 
jess74

jess74

Member
Well so far it seems to me that most people say to have the fans blowing in. If that's the case, (and I may be wrong or not thinking this out right) I would think it would be better to have the fans on top and with an open back canopy then the air would circulate better or should I say have a better flow? :notsure:
 
dburr

dburr

Active Member
Remember also, hot air rises. I would put them on the side and have planks across the top so most of it is open. Most of the heat will go out the top. Thats how I did mine (but no fans). The heat naturally rises.
My .02
 
mpls man

mpls man

Active Member
This is how i have my fans running now, i have 4 fans running for my canopy 2 on the top blow air in. 2 fans on the sides, 1 fan blows in, the other fan blows out, this is on my 75 gal. the temp never goes above 78* and the temp in the house is about 72* these are all 3" fans, i'm currently waiting for 2-3" varriable speed temp control fans that speed up faster when then canopy gets hotter, then slow down as the canopy cools off. good luck with deciding on your fans.
 
jess74

jess74

Member
Thanks everyone for the replies and suggestions.
Bill- thanks for the thread link, I don't know how I missed that thread in my search! Oh well, more info to digest! :D
 
dburr

dburr

Active Member
I just read that whole thread. :nervous:
I can't understand why they were worried about salt hurting the fans.:thinking:
Last I knew, salt is NOT in evaporated water. If it was our top-off would be salt water not fresh.:notsure: :D
 
jess74

jess74

Member
I'm not one to get into the logic of all that because I don't understand exactly. I do know that houses that are located near saltwater must use special paints, fixtures, and such because of the salt air. I would guess it’s the same principle. :thinking:
 
B

billb

Guest
Thats a good point! I don't know, but possibly it's other minerals etc. in Salt water, that seem to effect metals that get the moister around it.(look at boat maintenance) Interstingly enuf after I read that thread, I was just as confused as when I started (re: Push or Pull with the fans). My store bought unit pulls. If I were to build one I'd push on one side and pull on the other. Since the jury is still out on this one, and many people have tried both, I'd probably build a hood that could easily be converted either way. Most small fans will only change the temp a few degrees from what I can see(runnig compacs etc.), but that will in fact save you from buying a chiller in some cases. I'm actually getting border line right now, and the real summer heat has not hit yet. Side fans are definitly the choice. I'm out of my league here, but, I'd think with MH you would need a lot of cooling power, ie. 4 fans at least. If I went MH I'd raise the whole thing off the tank and lessen the chance of problems..but that is for the MH folks to discuss I guess...
Good Luck...
Billb
 
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