Water Heaters - The Great Sulfide Gas Mystery

OK. I'll admit my criminal past. I used to be an HVAC
contractor. Ahhhhhhhhhh!!

All kidding aside, there were many problems that I
attempted to resolve, not really caring about the
cause. If the homeowner was happy, so was I.

Hydrogen sulfide gas from water heaters was a problem
I dealt with often. Frequently, I would here the same
story from homeowners. They lived in the same house
for twenty, thirty, even fourty years. They never
drained their heater or replaced the anode rod. Even
when their heater was rusted and leaking they never
smelled any gas.

I get a call telling me they smell gas. The heater is
a mess so I replace it with a heater that has a solid
aluminum rod. They call me again because the gas
will not go away. I flush the system with bleach or
hydrogen peroxide. The smell goes away for several
days. Call number three tells me the gas smell has
returned. Finally, I replace the rod with a combo-
alloy rod made of aluminum, zinc, and tin. 95% of
the time that resolves the problem.

The question I always asked myself is why do people
live in houses for decades, let their water heaters rot
and never smell any gas. All of a sudden, for no
apparent reason they smell gas. Even when you
replace the heater the problem doesn't go away.
The chemistry, physics, and psychology involved in
this problem is beyond my feeble brain!