This piping is like a primary/secondary boiler
installation with a bypass in the secondary boil er
piping. Inlet water temperatures below 140°F (60°C)
can excessively cool the prod ucts of combustion
re sult ing in condensation on the heat exchanger and in
the flue. Condensation can cause operational prob lems,
bad combustion, sooting, flue gas spillage and reduced
service life of the vent system and related components.
The bypass allows part of the boiler discharge water to
be mixed with the cooler boiler return water to in crease
the boiler inlet temperature above 140°F (60°C). This
should prevent the prod ucts of com bus tion from
condensing in most in stal la tions. The bypass should be
fully sized with a bal anc ing valve to allow for proper
adjustment. A valve must also be provided on the boiler
discharge, after the by pass. Closing this discharge
valve forces water through the bypass. Start boiler
adjustment with the bypass valve in the full open
position and the boiler discharge valve half open. A
small amount of the high er temperature boiler discharge
water is mixed with the system water to maintain the
de sired lower system tem per a ture. A remote low tem -
per a ture range operator is recommended to control the
boiler operation based on the lower system tem per a ture.
This remote op er a tor should be wired across the R and
W terminals (see Room Ther mo stat Connection and
Terminal Strip Instructions).
FIG. 45 Boiler Piping with a 3-Way Valve
The installation of a three way valve on this boiler is not
generally recommended because most piping meth ods
allow the three way valve to vary flow to the boil er.
This boiler is a low mass, high ef fi cien cy unit which
requires a constant water flow rate for proper op er a tion.
Low flow rates can re sult in overheating of the boiler
water which can cause short burner on cycles, system
noise and in extreme cases, a knocking flash to steam.
These conditions can cause operational prob lems and
non-warrantable failures of the boiler. If a three way
valve must be installed, please pipe in a
primary/secondary system as shown in Figure 45.
Based on boiler sizing and system flow requirements,
this piping may still result in boiler short cycling.
FIG. 46 Boiler Bypass Piping
The heat exchanger is generally capable of op er at ing
within the flow rates of a residential heating system.
Should the flow rate exceed the maximum allowable
flow rate through the boiler (30 GPM) an external
bypass must be installed. The bypass should be fully
sized with a balancing valve to al low for proper
ad just ment of flow. Flow rate can be determined by
measuring the temperature rise through the boiler.
The basic guide for minimum flow in this boiler is
based on a 40°F temperature rise in most in stal la tions.
Low er flow and a higher temperature rise is acceptable
if the boiler system is specifically de signed for the
char ac ter is tics of a higher tem per a ture rise. A system
not specifically designed for a higher temperature rise
may experience over heat ing of the boiler water. This
can cause short burn er on cycles, system noise and in
ex treme cases, a knocking flash to steam. These
con di tions can lead to operational problems and
non-war rant able fail ures of the boiler. High
temperature rise systems must be designed by a
qualified engineer.
35
BOILER FLOW RATES
The maximum flow rate through the boil er with a
copper heat exchanger must not ex ceed 30 GPM.
ƽ CAUTION
