Specifications

Part number 550-142-120/0113
– 39 –
WM97+ gas-fired water boiler — Boiler Manual
Simplified pipe/circulator selection
1. Install the boiler and piping using the recommended piping
layouts shown in this manual.
2. Size the piping and components for each circuit in the space
heating system using Figure 41. At the flow rates listed, the
head loss in all piping will be 0.04 feet per foot of pipe.
a. Det
ermine the heating load (Btuh) for each circuit.
b. Calculate the flow rate for each circuit using its load.
c. To use a 20°F temperature drop, just divide the
MBH (1,000’s of Btuh) by 10.
d. Example — Flow for 20°F temp drop with 35,000 Btuh:
FLOW = 35 MBH / 10 = 3.5 gpm
e. Find the pipe size in Figure 41 that has a max flow rate
just larger than that required for the circuit.
f. Find the total equivalent length (TEL) of the circuit.
g. TEL accounts for losses through fittings and valves by
using the equivalent length of pipe that would cause
the same head loss. Add these numbers to the measured
length of the circuit to find TEL in feet.
h. TEL is usually close to 1.5 times the length of the
circuit for residential baseboard, radiator or con-
vector applications.
i. Measure the length of each circuit from the circulator
outlet back to its inlet. Then multiply this length times
1.5 to get the approximate TEL of the circuit.
j. Find the head loss for each circuit:
TEL = 1.5 X Circuit Length
(feet)
HEAD = TEL X 0.04
(feet water column)
k. NOTE: Size system header piping for the total flow of all
connected zones.
3. Example:
a. For a circuit with heating load = 45,000 Btuh (= 45 MBH).
Measured length of circuit is 88 feet.
b. Flow = 45 MBH / 10 = 4.5 gpm.
c. TEL = 1.5 x 88 feet = 132 feet.
d. From Figure 41, select 1" pipe (max flow = 7.1 gpm).
e. Head loss = TEL x 0.04 = 132 x 0.04 = 5.28 feet.
f. Select a circulator that can deliver at least 4.5 gpm at a
head of 5.28 feet. (Read the NOTICE below.)
To use this method, limit the flow through ¾"
finned-tube baseboard to 3.9 gpm, or use 1" base-
board and limit flow to 7.1 gpm. If the total load
of the circuit requires more flow, split the circuit
into two or more.
Figure 41 Flow rates for 0.04 feet head loss per foot of
pipe
(140°F water)
Pipe size
(inches)
MAX Flow rate (GPM)
@ 0.04 feet per foot
Pipe size
(inches)
MAX Flow rate (GPM)
@ 0.04 feet per foot
¾
3.9
2
45
1
7.1
2½
75
1¼
16
3
140
1½
24
4
290
Install relief valve
1. Install relief valve in ¾” street elbow piped from boiler supply
piping tee (Figure 6, page 13).
2. Pipe the relief valve only as shown, in the location shown.
3. Connect discharge piping to safe disposal location, following
guidelines in the
WARNING below.
To avoid water damage or scalding due
to relief valve operation, as per local or
state codes
:
Install relief valve ONLY with the spindle verti-
cal, as shown in illustrations in this manual.
Discharge line must be connected to relief
valve outlet and run to a safe place of disposal.
Terminate the discharge line in a manner that
will prevent possibility of severe burns or
property damage should the valve discharge.
Locate away from the top of the boiler.
Discharge line must be as short as possible and
be the same size as the valve discharge connec-
tion throughout its entire length.
Discharge line must pitch downward from the
valve and terminate at least 6” above the floor
drain where any discharge will be clearly vis-
ible.
The discharge line shall terminate plain, not
threaded, with a material serviceable for tem-
peratures of 375 °F or greater.
Do not pipe the discharge to any place where
freezing could occur.
No shutoff valve shall be installed between the
relief valve and boiler, or in the discharge line.
Do not plug or place any obstruction in the
discharge line.
Test the operation of the valve after filling and
pressurizing system by lifting the lever. Make
sure the valve discharges freely. If the valve fails
to operate correctly, replace it with a new relief
valve.
Failure to comply with the above guidelines
could result in failure of the relief valve to oper-
ate, resulting in possibility of severe personal
injury, death or substantial property damage.
Install water piping (continued)