If you have a bunch of hard drives in 5.25 bays using brackets, is cooling necessary on them?  I ask as my case has 11x5.25 slots, so I don't have a need for a 5in3

Yes ... and No 

 

Yes, they need to be cooled.

 

But No, they don't need dedicated hard drive coolers, which are often marketed for using drives in 5.25" bays.

 

The adapter brackets you're using already provide some addition convective cooling;  so all you need to do is ensure that there's good airflow in the case for the hard drives.  If there's space for front fans, that's the ideal solution ... 2 or 3 120-140mm fans would provide superb airflow for the drives.

 

Despite the fact you have enough bays; I'd still consider using these excellent 4-in-3 adapters, which have excellent airflow directly over the drives:  http://www.newegg.com/Product/Product.aspx?Item=N82E16817993002

those are too cheap to not say no.  thanks for the link!

You're most welcome.

 

They are not only inexpensive, but they cool the drives FAR better than any 5-in-3 cage I've tried ... including Super-Micro, Icy-Dock, and I-Star units.    The better cooling and far lower cost are easily a good tradeoff for the slightly less-convenient process of changing drives.

 

I have one of the coolmaster 4-in-3 units, and it serves it's purpose. Changing drives is more time consuming then I want it to be. For the next build, I think I'm going to try one of these:

 

ICY DOCK Black Vortex MB074SP-B 3.5" HDD 4-in-3

http://www.newegg.com/Product/Product.aspx?Item=N82E16817198059

That new Icy Dock unit looks very nice ... same cooling as the Cooler-Master, but with front-access drive trays for easy drive swaps.

 

I rarely change my drives; but that looks like a nice alternative to the Cooler-Master for a very modest additional cost (only $4/drive more).

 

... I don't know why all these manufacturers seem to think they need to use blue LED fans, however.  Nothing you can't fix with some wire snips (just cut the wires to the LEDs) -- but a nuisance to have to do so.    If I wanted "bling", I'd buy bling !!

 

 

I have 3 of the 4 in 3 cooler master drive cage I will sell for $10 ea. Plus shipping brand new in box.  All three for $25

 

http://www.newegg.com/Product/Product.aspx?Item=N82E16817993002&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=4003003&SID=d99yyeunemz6