Waterside Care and Requirements
3-2
750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
The air vent tapping on the top center line of the boiler should be piped into the expansion or compression tank.
Air trapped at the top of the boiler will find its way out of the boiler through the tapping.
3.2.1.1 — Minimum Water Temperature
The minimum recommended boiler water temperature is 170º F. When water temperatures lower than 170º F are
used, the combustion gasses are reduced in temperature to a point where water vapor condenses, causing corrosion
in the boiler and possible breeching.
Condensation is more severe on a unit that operates intermittently and which is greatly oversized for the actual
load. Condensation can be minimized by maintaining the boiler water temperatures above 170º F.
A temperature of 170º F is also recommended in order to provide a sufficient “temperature head” when No. 6 fuel
oil is to be heated to the proper atomizing temperature by the boiler water in a safety-type oil preheater. (The elec-
tric preheater on the boiler must provide additional heat to the oil if boiler water temperature is not maintained
above 200º F.
3.2.1.2 — Rapid Replacement of Boiler Water
The system layout and controls should be arranged to prevent the possibility of pumping large quantities of cold
water into a hot boiler, which will cause shock or thermal stresses. Water temperature in a boiler of 200º F or 240º
F cannot be completely replaced with 80º F water in a few minutes time without causing thermal stress. The same
fact applies to periods of normal operation, as well as during initial startup.
When individual zone circulating pumps are used, it is recommended that they be kept running, even though the
hear users do not require hot water. The relief device or bypass valve will thus allow continuous circulation through
the boiler and can help prevent rapid replacement of boiler water with cold zone water.
3.2.1.3 — Continuous Flow Through the Boiler
The system should be piped and the controls arranged to allow water circulation through the boiler under all oper-
ating conditions. The operation of three-way valves and system controls should be checked to be sure that the
boiler will not be bypassed. Constant circulation through the boiler eliminates the possibility of stratification within
the unit and results in more even water temperatures to the system.
A rule of thumb of 3/4 to 1 gpm per boiler horsepower can be used to determine the minimum continuous flow
rate through the boiler under all operating conditions. The operator should determine that a flow of water exists
through the boiler before initial firing or refiring after the boiler has been drained.
3.2.2 — Water Circulation
The following chart shows the maximum gpm circulation rate of boiler water in relation to full boiler output and
system temperature drop.
NOTE: If the operating water temperature going to the system must be lower than 170º F, the operating boiler water
temperature should be a minimum of 170º F (200º F if used to preheat No. 6 oil) and mixing valves should be used to
avoid damage to the equipment.
NOTE: The circulating pumps should be interlocked with the burner so that the burner cannot operate unless the cir-
culating pump is running in order to avoid damage to the equipment.
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