PART NO. 100266523
– 5 –
DRAIN
STORAGE
TANK
TEMPERATURE
CONTROLLED
IWH
HOT
T&P
VALVE
CIRCULATOR
PUMP
EXPANSION TANK
(OPTIONAL)
COLD
COLD
MIXING
VALVE
CHECK
VALVE
T
Figure 2. Single Storage Tank Plumbing for a
Temperature Controlled IWH
T
COMBINATION INLET/
DRAIN VALVE
STORAGE
BOOSTER
TANK
NON-
TEMPERATURE
CONTROLLED
TANKLESS COIL
BOILER
HOT
HOT
T&P VALVE
CIRCULATOR
PUMP
CHECK VALVE
EXPANSION TANK (OPTIONAL)
PRESSURE
REGULATOR
(OPTIONAL)
COLD
COLD
MIXING
VALVE
Figure 3. Single Storage Tank Plumbing for a Non-
Temperature Controlled Tankless Coil Boiler
5.
Pay attention to the desired flow direction when installing
the circulator pump. If the pump does not have a check
valve embedded install one to ensure the desired flow
direction is maintained during system operation.
6. Install a mixing valve with the hot port going to the top
tank fitting. Connect the domestic hot water supply line
to the mixing port of the mixing valve. Connect the cold
port of the mixing valve to the cold water supply line and
place a shut-off in this line. Most mixing valves do not
operate properly if the pressure differential between hot
and cold port is too high. If this happens, lower mixed
water temperature will be provided. The shut-off valve
should be used to adjust this pressure differential. Set
the mixing valve outlet temperature to 49°C (120°F) to
avoid scalding.
7. A check valve may be installed in the cold water line before
the connecting tee.
Note:
The check valve can often be noisy and cause
reduced supply pressures. For multiple storage tank
systems, check valves must be installed to prevent the
circulator pump from pumping hot water into another tank
and overheating it.
8. The use of a pressure regulator is optional, but
recommended when the cold supply pressure is over
80 psi. Reducing the inlet pressure to 45-60 psi will
reduce probability of relief valve discharge due to thermal
expansion.
9. The water utility supply meter may contain a check valve,
back-flow preventer or water pressure-reducing valve.
This will create a closed water system. During a heating
cycle, water expands creating a pressure buildup in the
water system. A Temperature and Pressure (T&P) Relief
Valve must be installed (150 psi maximum pressure).
See preceding section. If the T&P valve discharges
periodically, it may be due to thermal expansion in a
closed system. To prevent this condition and to reduce
the possible buildup of lime on the T&P Relief Valve seat,
install a thermal expansion tank in the circulating loop as
shown in Figure 2 and Figure 3.
10. Some jurisdictions require a Vacuum Relief Valve to be
installed. Such a valve allows air to enter the piping system
thus preventing vacuum conditions that could siphon
water from the system. Check local code requirements.
