I was just thinking about this today, and it crosses my mind from time to time, so i thought I'd share, and see what you guys do.
Seems like the other plumbers in the area put the thermal tanks on the hot side. Why? Doesn't excessive amount of heat ruin rubber? Thats what the guts in them things are, aren't they?
I was at a Grundfos seminar about a year ago, and this guy (company rep) was talking about recirc systems and hot water heaters, and somehow-or-another, he got to talking about expansion tanks, and he says "and what side do we put the expansion tank on?" Like zombies everyone else replied "on the hot side". Then he asks : "And why do we do that?" followed by the sound of crickets. He answered his own question with : "because hot water heaters have that little heat trap check valve nipple that won't allow the expanded water to flow back into the cold piping.
I was dying to ask the question "So are you telling me that you can fill a hot water heater to pressure through the hot nipple, and nothing will come out the cold side?"
His claim seemed outrageous without even giving it a second thought, and it got me wondering how many people are putting them on the hot side. I've been taught to put on the cold because supposedly it will last longer.
How are you doing it and why? Maybe this has been discussed and I missed it.