HDD may be failing; not sure

22F is too low. http://www.buildcomputers.net/hdd-temperature.html

22C would be just fine.

But if as you say you have backups (plural is so important) then can you recover your system if it fails today?

That is, some folk don't have recovery media (didn't make, keep or obtain.)
Bob

While it's interesting to read drive firmware might be available for this drive (read http://community.wd.com/t5/Desktop-Mobile-Drives/WD1002FAEX-00Z3A0-Firmware-05-01D05-No-Cache/td-p/64640 and ask WD!) it's possible this drive has newer firmware. I rarely update this but if a drive exhibits failures I duplicate the drive for safety then update the firmware and the restore from backup.

In your case you don't seem ready for all this work so this post is just to fill in something we didn't cover.
Bob

Your computer should -not- be losing files.

I use Active SMART to monitor my hard drives. It'll tell you if a drive is going bad.

If you are losing files, get a new HD. A good one that has a 5 year warranty.

Did you check for viruses?

...so much so, I almost hesitate to add to it. The common thread is BACKUP. You can choose to do this or not, just ask yourself what your data is worth to you? You've backed up your critical data, you say, great, I hope you made multiple copies. The stuff you haven't backed up, you say is software and such that you can rebuild, though in your own words, you say that is a pain. How much of a pain?

As Bob has pointed out, image copy backups and restores are comparatively quick, I'd guess half an hour or so for terabyte and a half, unlike file copies, which can take several hours for the same data. The downside to an image copy is that you generally can't restore individual files. Your choice.

A 2 TB desktop external HDD (3.5", self powered, the USB powered "portable" ones are significantly more) is $99 Australian here, so less USD. That looks to me to be cheap to protect all my data and software and avoid the pain of a manual rebuild but your mileage may vary.

Now about your system disk. I think the temperature is a red herring. Hard disks fail, fact of life. How soon? Depends on too many factors to make a reasonable guess but a rough guide is to check the manufacturer's warranty but then I have a couple of disks (not in critical use!) that won't see their 20th birthday again!

Sometimes (relatively rarely) they will go "poof" and that is the end of them and you are very glad you have a couple of up to date backups! But more often, they send early warnings such as you are getting now. You can ignore them and wait for the "poof" if you choose or you can do, as you have done, and investigate the issues with as many tools as you can find. Your manufacturer's tool is flagging a fail, that says the fault is real and you continue to use the disk at your own risk. The manufacturer's don't flag these errors for fun, they mean it.

There are circumstances when you might choose to go on using the disk and rely on your backups, or you may take the hint and replace the disk. Again entirely your own choice.

Could you wipe the disk, low level format it and try a restore on to it? Yes but there is no guarantee that this will work - it might. But remember it was the manufacturer who flagged the fail; suppose you follow this route and the disk apparently comes up clean? That intermittent fault is still there, waiting to pop up again when you exercise the issue that encountered it in the first place. Next time, it may not be a few ad hoc files that you don't really care about, it may be the key to all your valuable data. Worth the risk for a hundred bucks? Your choice entirely, mine would be to heed the warning and replace.

Twenty two degrees C is equivalent to 71.6 degrees Fahrenheit and one would have to question by any imagination that would cause any operational problem with a PC. Most electrical equipment have two spec ranges: a storage ,and operational and as you would surmise the storage is much winder ( ie IBM 60=>. 90 F on and 50=. 110 F off) The FLA area is notorious for lightening and rain and I would recommend any one in that region use a UPS and anti static mat to protect their PC investment. IC damage can occur from ESD at about 10 pico joules 10XE(-9)( a watt is 1 joule per second) and the simple power strip most users use provide a very low level of protection.
From a PC stand point the 2 least reliable items are the power supply and hard drive. From my personal view point any second or third party program or App used to check performance I treat with skepticism because most I do not think have the technical depth nor regression test disciple for those types of products. Using the designer and builder's (WD) test will probably be based on what they use to deliver their hardware and based on their years of experience would be my first choice.
There are 2 basic issue in replacing a hard drive; Data recovery and loading the Apps and operating system. With the very large drives one should have a relative small partition for the OS( Or I use 120GB SSD drive C for mine) and then use the large drive for data and Apps. I have personally used ACRONIS True Image ($) in the past with very good success and once the image was installed booting and using was just like the " old" drive.
It is not clear from your post if the chkdsk has the /f switch set which will have it attempt to correct disk errors. There are other artifacts which can cause errors , ESD as noted above, power supply problem ( noise ) or how one shuts it down. Just switching off is not a good approach since the flying heads can crash into the disk vs park at a planned location like windows when you shut down using it.
You do not have a hard failure and if it was my decision I would run the WD test periodically and look for trends of increasing errors. That has to be tempered by disk age, how often you power cycle ( once per day is generally recommended but do not let run over night vs fire hazard concern), audible noise increases from etc.
You should back up your data and if it does fail the only loss will be the relative short time to install, format the present OS ( You have the install disk I hope?). Except you of course will not have all the updates which will be additional effort This link http://www.techsupport alert .com ref " Never Re-install Windows Again" you may find use full
good Luck