Burnham FREEDOM Installation, Operating And Service Instructions page 50

Method 2: Direct Connection to Heating System (Generally NOT Recommended)
The FCM can be connected directly to the heating system as is done with conventional boilers (Figure 9.8). If
this is done, the flow rate through the boiler will equal the flow rate through the system. The flow rate through the
system must therefore always remain within the limits shown in Table 9.1. For this reason, the pressure drop through
the entire system must be known, added to the boiler pressure drop, and a circulator selected which will provide the
required flow at the total calculated pressure drop.
This method is generally not recommended because it is often very difficult to accurately calculate the pressure
drop through the system. In replacement installations, it may be impossible to get an accurate measurement of the
amount of piping and number of fittings in the system. In addition, if the system is zoned, the system flow may drop
well below the minimum required when only one zone is calling for heat.
The one advantage to this method is its installation simplicity. It may make sense to use this method when the
boiler is to be installed with a new single zone system having a low-pressure drop. Pressure drop curves for the
FCM Series boilers are shown in Figure 9.9. Calculation of the system pressure drop, and selection of the
circulator, must be performed by someone having familiarity with pressure drop calculations, such as an HVAC
engineer.
Figure 9.8: Piping Method #2 - Direct Connection of boiler to Heating system
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