Closed Loop System
A system becomes closed when a Check Valve or a back-
flow prevention valve is installed in the cold water piping
upstream of the water heater.
A check valve will prevent water being relieved into the
cold water system due to pressure created when
water is heated in the water heater.
5
WATER HEATER
DOMESTIC HOT WATER
SUPPLY AIR
BLOWER
HEATING COIL
RETURN AIR
COLD WATER INLET
ANTI-SCALD VALVE
(WHEN REQUIRED)
VALVE
(shut off)
VALVE
(shut off)
VALVE
(shut off)
VALVE
(balancing)
COOLING COIL
(OPTIONAL)
DRAIN
VALVE
EXPANSION TANK
OR OTHER MEANS
(WHEN REQUIRED)
CHECK
VALVE
Combo System Basic Principles
Open and Closed Systems
Open and Closed systems both deliver hot water and space
heating.
Water systems that incorporate a pressure tank (i.e. well
systems) are normally Open Systems and most municipal
water systems are Closed Systems.
Drain Valve
A drain valve is required to allow the heating loop to be
drained for service or repair and to remove air from the
heating loop when commissioning a system. The drain
valve should be near the low point of the return piping sys-
tem to be near the water heater. Ball, Globe or Gate Valves
are suitable for drain valves.
ATTENTION
Check valves should always be installed in a
vertical rise with the flow of water shown.
IMPORTANT
Refer to local codes, local bylaws and installation
manuals supplied with water heater before starting
any installation work.
This Check Valve
minimizes Thermo-
Siphoning. Thermo
Siphoning is the cold
water backflowing
through the heating
loop when domestic
hot water is called
for.
Conventional
Cooling Coil
(Not available
through Airia)
