How big of a Fan do I need?

[psyco_guy_abd]

Hey guys, with temps getting into the mid 80's now I'm looking for a way to help keep my tank cool. I was thinking of adding a few fans to blow water across the surface of the tank but I was wondering how big of a fan do I need. The problem is that I only have about 2-3 inches between the lights and the water so the fan has to fit in that space. I could get some of the 60mm computer fans in there but I'm wondering if the 10 - 20 CFM that they move would be enough. Any thoughts?

[Aimforever]

I'm not sure how big your tank is, but all it took to drop the temp from 84 to 79 on my 36 gallon was a single computer fan (roughly 3 inches across) pointed straight down at the surface of the water. My evaporation is much faster now though... I top off with about a gallon every 36 hours. It used to be a gallon per week at most. HTH

[psyco_guy_abd]

Thanks for the quick reply. My tank is 75 gallons. I guess if one was able to drop your temp then I guess my plan will most likely work out. I was going to mount 4, two blowing in and two pulling air out on the opposite end. Then I was going to build one of those variable speed controller things that was posted on here a day or two ago to run them on.

[AZDesertRat]

Can you clip a $8 Walmart 7" fan on the tank rim somewhere? I have used those for years both over a tank and over a sump and you can easily lower temps 5 degrees with a single fan.

Twn fans blowing in and two out only gives you the CFM of two fans. My 100G canopy is completely enclosed all around including the top so I put one 4" fan in each end blowing across the length of the bulbs and drilled 2, 4" holes in the top directly over the reflectors for heat to escape both by convection and from the fans. Works great. I also still have a clip on fan over the sump on a Ranco controller so if the temp goes up 2 degrees it comes on as a back up.

[Aimforever]

I didn't see the thread about building a variable speed controller, and I'm not sure how much it cost or how much time it would take you to build it, but for mine I just used a variable voltage AC to DC power adapter from RadioShack. I just wired the fan directly to it, and by sliding the switch on the front, you can adjust the voltage (and hence the speed) of the fan. Just something to think about if there was a lot of work involved in the DIY project. I'm not sure if this link will work... if not just search for "3-12V Regulated 1000mA AC Adapter".

http://www.radioshack.com/product/index.jsp?productId=2552560&cp=&sr=1&origkw=ac+adapter&kw=ac+adapter&parentPage=search

[Randall_James]

<a href=showthread.php?s=&postid=10015651#post10015651 target=_blank>Originally posted</a> by AZDesertRat
Can you clip a $8 Walmart 7" fan on the tank rim somewhere? I have used those for years both over a tank and over a sump and you can easily lower temps 5 degrees with a single fan.

Twn fans blowing in and two out only gives you the CFM of two fans. My 100G canopy is completely enclosed all around including the top so I put one 4" fan in each end blowing across the length of the bulbs and drilled 2, 4" holes in the top directly over the reflectors for heat to escape both by convection and from the fans. Works great. I also still have a clip on fan over the sump on a Ranco controller so if the temp goes up 2 degrees it comes on as a back up. Absolutely...
trying to do with with variable speed PC fans is both a pain and just more expensive. I just run the fan with my light cycle although the Ranco controller would be a worthwhile investment.

[Dave12678]

<a href=showthread.php?s=&postid=10015651#post10015651 target=_blank>Originally posted</a> by AZDesertRat
Can you clip a $8 Walmart 7" fan on the tank rim somewhere? I have used those for years both over a tank and over a sump and you can easily lower temps 5 degrees with a single fan.

Twn fans blowing in and two out only gives you the CFM of two fans. My 100G canopy is completely enclosed all around including the top so I put one 4" fan in each end blowing across the length of the bulbs and drilled 2, 4" holes in the top directly over the reflectors for heat to escape both by convection and from the fans. Works great. I also still have a clip on fan over the sump on a Ranco controller so if the temp goes up 2 degrees it comes on as a back up.

That fan kicks @ss. It would work perfect for a 75g, on my 54g I have to turn it off it gets to cold depending on the temp the ac is set on. Its a great fan and cheap pick one of them if you can.

[psyco_guy_abd]

Here is a link to the DIY variable speed controller...
Link (http://www.reefcentral.com/forums/showthread.php?s=&threadid=1127852)
It controls the speed based on temperature and its only like $5. I like the idea of the PC fans because I think it will look cleaner installed flush in the hood rather then having a big fan sticking up. I do have a clip on fan, just got it yesterday but I'd like to keep that a temporary solution. Does anyone know how many CFM the 6-7" clip on fans are?

[Aimforever]

Wow very nice. I think I'll try that myself when I get the time. Thanks for the link!