What I mean is that heat damages sperm, that is why when it's hot out your balls relax and seem to hang down to your knees. (not literally of course) Conversely, when the testes get too cool, they retract pulling the testes in close to the body in order to warm them up.
Again let me stress that I'm no expert but if you talk to a specialist the first thing they advise for people who have problems getting pregnant is to either switch to boxers or go commando (although I'm sure they wouldn't say it quite like that) The reason for this advice is to allow the testes to fuction as they should.
What this tells me is that if you do warm ups using a heat pad or even rice sock, your intentionally heating the testes in order to cause them to relax and descend. Get carried away with the heat and the testes won't be able to cool the sperm properly which could cause problems getting pregnant.
The bottom line is, if you want to get pregnant and it's not happening ease up on the heating pad. Otherwise, barring an injury from overdoing it, Penis Enlargement can only help you become more fertile because of the increased circulation and vascular health that Penis Enlargementing promotes. Not to mention the increases in testosterone resulting from a healthy prostate.
So, no worries...Penis Enlargement all you like.