30C is pretty warm for the room - at that temperature a hard drive at 50-55C is probably not unreasonable. It might be a little better if you could get the temperature down into the high 40s, but the drive will work fine at 50-55C. It just might have a slightly higher chance of failing a little bit sooner.
Well now you have some data - you can see what a reasonable temp should be for a HDD. I have always shot for the 40s or cooler. It may run at 50 and 60c but the life of the drive will fall. If you continue to have cooling issues, you might want to look into a 5.25 HDD bay with active fan.
I have a slim box and according to the S.M.A.R.T. data on my hard drives they both hit 72C. At which point they both overheated with loud noises. I pulled the plug and left it off a couple of days. One drive has 99 bad sectors now, and the other only 1 bad sector... this is in balance with the usage. Fortunately they both are in working condition.
For Linux users I've created a cron job to protect your computer in case the hard drives are getting to HOT. I put my max limit at 48C with warnings before then. With basic usage I max at 45C. With intense usage I average 55C. Although I have pushed it to see how quickly it would go up. If I can't maintain a temp below 48 I'll have to better ventilate my computer and add more fans. Here's the script https://gist.github.com/3594541