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

My concern is whether option (2) -- easy, cheap, etc. -- is a good idea
long-term. Will constant slight "blowing" of the valve cause it to fail
catastrophically?

I found this on one site:
"T&P valves are strictly an emergency measure and should be replaced every 2
years. At 180 psi , the temperature that the T&P valve opens, damage can
occur to your system and you may have voided the warranty on your water
heater."
and:
"Plumbing codes require that thermal expansion control be addressed in
plumbing systems. A temperature and pressure relief valve is not considered
a thermal expansion device. This is because when water is allowed to
continuously drip from the T&P relief valve, minerals from the water can
build up on the valve, eventually blocking it. This blockage can render the
T&P valve useless and potentially lead to hot water heater explosions."

Obviously these concern me! I just don't want to $pend more dollar$ if I
don't have to, though it sure sounds like I do have to.

Thanks in advance for any thoughts,

....phsiii