Closed/Open Combo System
From the aspect of delivery of domestic hot
water and space heating, the Open and Closed
systems operate the same. A system becomes
closed when a backflow prevention valve or
check valve is installed in the cold water piping
upstream of the water heater. A backflow
prevention valve will prevent the pressure created
when water is heated in the water heater, from
being relieved into the cold water system.
Therefore, an expansion tank (or equivalent
device) may be installed as part of any closed
system. The operations of the valve and
expansion tank are discussed later in this
section of this manual.
Note: Water systems that incorporate a pressure
tank (well systems) are normally open systems.
5
Combo System Basic Principles
SCHEMATIC SYSTEM
DIAGRAM
(Closed Loop System)
SCHEMATIC SYSTEM
DIAGRAM
(Open System)
Note:
Plumbing components and system
configuration may vary from diagram
portrayed. Refer to local codes, local
bylaws and installation manuals
supplied with water heater before
starting any installation work.
