SDT/SET
Installation & Operation Manual
12
4
Domestic Side (Tank) Piping
Basic Domestic Piping
Figure 4-2 on page 15 shows typical domestic water piping
for a tank. The function of the components shown are as
follows:
a. Shut-off valves (recommended) - Used to isolate the
tank for servicing.
b. Backflow Preventer (required by some codes) - Used to
prevent water from backing out of the tank and into
the main potable water supply in the event that inlet
water pressure drops.
c. Expansion Tank (required for thermal expansion)-
Absorbs the increased volume caused by heating water.
Use an expansion tank designed for use on
domestic water systems. Refer to the expansion tank
manufacturer’s literature for the proper size expansion
tank to use.
NOTICE
When an expansion tank is used, do not
put any valves between the expansion
tank and tank inlet.
d. Unions (recommended) - Used to disconnect the tank
in the unlikely event that this is necessary.
e.
Drain (required) - Used to drain the tank for inspection
or
servicing.
Multiple Tank Domestic Water Piping
The two pipe reverse return piping uses more pipe than the
two pipe direct return piping, but the flow is more balanced
and even in the two pipe reverse return piping layout
(see FIG. 3-4).
Each tank must have its own T&P valve. It is recommended
that each tank be equipped with its own isolation valves,
unions, and drains so that one tank may be removed from
the system. If local codes require a backflow preventer,
check with the appropriate authority to find out whether
one backflow preventer may be used for tanks or each tank
must be equipped with its own backflow preventer. If each
tank must have its own backflow preventer, each tank must
also have its own expansion tank. If a common backflow
preventer is permitted, an expansion tank must be sized to
accommodate the expansion volume of all tanks.
Domestic Water Piping for Distant Fixtures
In some cases the furthest fixture may be quite distant from the
tank. Such an installation would result in an unacceptable delay
before hot water reaches these distant fixtures. Even if all the
fixtures are relatively close to the tank, the building owner may
want hot water at all fixtures as soon as they are opened.
To prevent delays, return circulation piping with a check valve
that allows flow to the inlet of the tank. This should be installed
on each branch circuit at the farthest fixture or device, so that
hot water is supplied upon demand.
Because hot water is always circulating in the hot water branch,
the entire branch should be insulated to prevent excessive heat
loss.
