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GSA
Gas-Fired Steam Boilers –
Boiler Manual
13
Part Number 550-110-738/1012
3 Install piping
continued
Condensate return
Modern steam boilers are designed to steam for less time than
older, larger boilers. When replacing an older steam boiler the
system condensate return time may be longer than the steaming
time. This could cause the following problems:
1. Boilers fitted with an automatic water feed could overfill.
2. Units fitted with only a low water cutoff would shut down and
cycle while waiting for condensate to return.
Following is a simple method for determining whether or not a
reservoir pipe is required to lengthen steaming time for a
residential installation:
1. Disconnect condensate return line at existing boiler.
2. Heat
boiler and allow to steam for 10 minutes. Turn off
boiler.
3. Measure length of time from when boiler started to steam to
when condensate begins to return through condensate line.
4. Measure length of time from when condensate begins to return
to when it stops returning. Divide this time by 2.
5. Add time measured in step 3 to time calculated in step 4. This
sum is the average time required for condensate to return to
the boiler.
6. If this total time is 10 minutes or less, no reservoir pipe is
needed.
If total time for condensate to return to boiler (from step 5) is
more than 10 minutes, a reservoir pipe (or boiler feed system)
is recommended. See Table 7, page 12, for suggested reservoir
pipe size. Install as shown in Figure 14.
For larger systems (as noted in Table 7), use a boiler feed system
with a condensate tank and feed pump. You will have to install a
low water cutoff/pump control on the boiler to operate the pump.
Use Table 8 to size boiler feed systems. See page 7, Table 4, for
tapping locations. (The use of a combination condensate tank and
float‑controlled condensate return pump is not recommended.)
For most residential installations a reservoir pipe may be all that
is necessary to ensure proper operation.
Figure 14
Recommended piping for parallel-flow systems with
optional reservoir pipe