A.Dave Yates, a plumbing
contractor in York, Pa., responds: This initiative
actually got its start in Canada, when the Canadian Institute
of Plumbing and Heating (CIPH) began requiring 140°F
minimum temperatures in storage-tank water heaters to suppress
bacteria numbers. This measure is aimed in particular at
Legionella pneumophila sero-group 1, the bad boys that cause
legionellosis, or legionnaires' disease, a pneumonialike
Estimates of the number of deaths from potable hot-
water system bacterial infections range widely, but 10,000 per
year is the middle ground. Roughly 25 percent of all potable
water heaters have measurable levels of Legionella pneumophila
SG1, which thrive in water temperatures between 95°F and
These bacteria begin to die off only when the temperature rises
above 131°F — but because of stratification (where
cooler water sinks to the bottom), 140°F is the minimum
recommended setting for a storage-tank water heater.
You can't contract the disease by drinking or bathing in
infected water; you have to breathe in the bacteria, which is
carried by fine water droplets.
Of course, once you raise water temperatures high enough to
kill bacteria, scald protection becomes increasingly important.
CIPH now requires an ASSE-certified thermostatic mixing valve
at the water heater's outlet, or ASSE-certified 1016
scald-guard faucets or valves installed at each point of
A single ASSE 1017 point-of-source mixing valve costs less than
multiple valves, but either approach will add to the cost of
plumbing a house.
Unfortunately, code changes come slowly in this country, and
until now our code bodies have largely ignored this issue. One
reason is that a change like this requiring an additional layer
of antiscald protection marginally increases construction
costs, so it's been opposed by many builders' groups.
Nevertheless, the code changes you've already seen in your
state are just the beginning of what will soon become a
A mixing valve installed at the water heater reduces
domestic hot-water supply temperatures. The outlet temperature
of the ASSE 1017 point-of-source mixing valve shown here is
adjustable from 80°F to 120°F.