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Special Applications
Combination Space Heating/Potable
Water System
Some water heater models are equipped with inlet/outlet
tappings for use with space heating applications. If this
water heater is to be used to supply both space heating
and domestic potable (drinking) water, the instructions
listed below must be followed.
• Be sure to follow the manual(s) shipped with the air
handler system.
• This water heater is not to be used as a replacement
for an existing boiler installation.
• Do not use with piping that has been treated with
chromates, boiler seal or other chemicals and do not
add any chemicals to the water heater piping.
• If the space heating system requires water tempera-
tures in excess of 120°F, a tempering valve or an anti-
scald device should be installed per its manufacturer’s
instructions in the domestic (potable) hot water supply
to limit the risk of scald injury.
• Pumps, valves, piping and fittings must be compatible
with potable water.
• A properly installed flow control valve is required to pre-
vent thermosiphoning. Thermosiphoning is the result
of a continuous flow of water through the air handler
circuit during the off cycle. Weeping (blow off) of the
temperature and pressure relief valve (T & P) or higher
than normal water temperatures are the first signs of
thermosiphoning.
• The domestic hot water line from the water heater
should be vertical past any tempering valve or supply
line to the air handler to remove air bubbles from the
system. Otherwise, these bubbles will be trapped in the
air handler heat exchanger coil, reducing the efficiency.
• Do not connect the water heater to any system or
components previously used with non-potable water
heating appliances when used to supply potable water.
Some jurisdictions may require a backflow preventer
in the incoming cold water line. This may cause the
temperature and pressure relief valve on the water heater
to discharge or weep due to expansion of the heated water.
A diaphragm-type expansion tank suitable for potable
water will normally eliminate this weeping condition. Please
read and follow the manufacturer’s instructions for the
installation of such tanks.
Also see Water System Piping for additional instructions on
the safe and correct installation and operation of this water
heater.
Coil
Must be vertical to
remove air bubbles
Figure 16
Typical Tempering Valve Installation
Combination Space Heating/Potable
Water Heating System
Domestic
Hot Water
Out
Tempering
Valve
Hot
Water
Out
Unions
Cold
Water
Inlet
Pump
Flow Control
Valve
To
Air
Handler
Out
In
Air
Handler
Shut-off
Valve
Massachusetts code
does not allow this
type of installation.
Solar Installation
If this water heater is used as a solar storage heater or as a
backup for the solar system, the water supply temperatures
to the water heater tank may be in excess of 120°F. A
tempering valve or other temperature limiting valve must
be installed in the water supply line to limit the supply
temperature to 120°F.
NOTE: Solar water heating systems can often supply water
with temperatures exceeding 180°F and may result in water
heater malfunction.