Install Instructions

4 Hydronic piping (continued)
31
Installation & Service Manual
Low Temperature Bypass
Requirements
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 for temperatures lower than 100°F.
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 in Section 5 of this manual).
Three Way Valves
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. Based on boiler sizing and system
flow requirements, this piping may still result in boiler short
cycling.
Boiler Flow Rates
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.
TABLE - 4D
MAXIMUM FLOW FOR HEATING BOILER
The maximum flow rate through the boiler with a copper
heat exchanger must not exceed the following:
Model Maximum Flow
Maximum Flow for
CuNi Heat Exchanger
90,000 - 500,000 30 GPM 38 GPM