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About four months ago, we replaced our electric water heater. Last weekend
the pressure relief valve started dripping small amounts of water
intermittently. Some research/analysis resulted in a diagnosis of high
pressure due to a one-way valve between us and the street; sure enough, it
drips worse when we don't use water for long periods. And it only started
recently because we have an Aprilaire humidifier (the kind that has a
trickle of fresh water running through it whenever it's running), and of
course just turned that off for the spring.

So. The question is: do I *need* an expansion tank? I was given two
options:
1) Expansion tank.
2) Just run a tube from the valve to the floor drain nearby


Put the exp tank on; they are inexpensive and required.

If you just let it drip, the whole system is over-pressured,
which can be damaging. Plus, the relief valve will soon wear out.

Jim