Bradford White SW-2-40R-L Installation And Operating Manual page 13

Pre-installation continued-
IMPORTANT DECISIONS REQUIRED BEFORE
SIZING
1. Boiler DOE Heating Capacity – The indirect-fired water heater
will provide the rated performance only if used in conjunction with
a heat source with a DOE heating capacity (Boiler Output) at least
as much as the minimum noted in Table 3. If the heat source has
less capacity, the output of the tank will be reduced. To determine
the approximate reduction in output from the tank use the
following formula:
New Rating = (maximum continuous draw rating) x
Actual Boiler Output Capacity
Minimum Boiler Output Capacity
For example, what would the continuous draw rating be if a 50-gallon
indirect-fired heater were installed with a heat source having a DOE
heating capacity of 110,000 BTU/h?
Answer:
New Rating
= 180 gal/hr x (110,000 BTU/h)/(120,000 BTU/h)
= 180 gal/hr x 0.917 = 165 gal/hr
Increasing the boiler DOE heating capacity above the values
listed in Table 3 will not increase the rating of the water heater.
2. Circulator Sizing – Refer to Table 5 for the corresponding
pressure drop through the coil for the given model. Calculate the
pressure drop of all straight pipe and fittings on the supply and
return of the water heater at the selected flow rate. Add the
piping/fitting pressure drop to the pressure drop through the water
heater coil.
Select a circulator that will provide an appropriate flow rate at the
combined pressure drop.
INSTALLATION
NOTICE
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