• The tank should be drained and flushed
annually to remove any accumulation of lime,
iron and other minerals. If lime is found, water
softening equipment should be considered.
• Anodes should be inspected at least yearly
and replaced once they are down to one-third
of their original size or show signs of pitting.
• If a “rotten egg” odor is present in the hot
water, flush the tank with a manufacturer- approved
solution and replace the magnesium
anodes with new aluminum anodes.
42 National Oilheat Research Alliance
Safety considerations
Figure 13
Scalding and Legionnaires Disease
Water temperatures above 125°F can cause severe burns and death from scalds. Children,
the disabled, and elderly are at the highest risk from being scalded. This is because they
respond more slowly to exposure. The human threshold for pain is 118°F, and scalding occurs
over 125°F. A proper installation will have appropriate valves to protect against scalding
hazards.
NORA recommends the use of thermostatic anti-scald mixing valves on all hot water destined
for domestic use. Having these devices on appliances will also help to ensure that the
house has sufficient hot water.
Using mixing valves allows us to solve a significant problem that could occur if we merely
set the hot water tank to 120 degrees. Low or warm water temperatures allow the bacteria
that cause Legionnaires disease, a severe form of pneumonia, to thrive. It is recommended
that water temperatures be set at 140°F to kill the bacteria and the mixing valve be adjusted to
deliver the correct temperature to the faucets.
Temperature & Pressure (T&P) relief valve
The discharge drain tube of the T&P valve must be made of material that is rated for a
minimum of 150 psi and temperatures of at least 120° F and installed so it terminates plain (not
threaded) 6” above the floor drain.
Hydrogen gas
If a water heater equipped with anodes has been out of service for a period of time, the
guidelines contained in UL 174 should be followed”
“Hydrogen gas can be produced in a hot water system served by this heater that has not
been used for a long period of time (generally 2 weeks or more). Hydrogen gas is extremely
flammable. To reduce the risk of injury under these conditions, it is recommended that the
hot water faucet be opened for several minutes at the kitchen sink before using any electrical
appliance connected to the hot water system. If hydrogen is present, there will probably be
an unusual sound, such as air escaping through the pipe as the water begins to flow. There
should be no smoking or open flame near the faucet at the time it is open.”