So, while we're on this subject, my water heater is now in the 12th year of its five-year warranty. It's been no trouble, but I'm wondering whether I should replace it "just because."

For all those thinking that putting the WH in a pan with a 1" drain hose is going to protect you from leaks: You should have seen when my old heater failed. It was quite spectacular, with water shooting out of the flue opening like a geyser. No way would that have been contained by any reasonable pan.