iMac 21.5 late 2013 idle fan speed I recently upgraded my HDD to a SSD. Before upgrading I never checked fan speed.
Now, after my upgrade the fan spins at 1400 rpm on idle. 

Is this normal? I thought it would be quiet like on a MacBook Pro, with the fan turning on after it reaches a certain temperature. However, it seems to me the fan is now on sooner and because of this my iMac is noisier than before.

Can someone who has original hdd check fan speed and temperature and post it here?
A fan speed of 1400RPM really is nothing to worry about. And your model iMac does not require an external thermal sensor for an ssd upgrade, so that shouldn't be an issue for you.

My first step would be to try resetting your System Management Controller. To do this:


Shut down your computer
Unplug it from power
Wait 15 seconds
Plug the power cord back in
Wait for an additional 5 seconds
Press the power button to turn it back on


Software option

You can also try installing SSD Fan Control to see if that resolves your issue. However, I would only do that if the SMC reset does not resolve your issue.