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Table F: Domestic Water Heater Flow Rate Requirements
ΔT = Temperature rise, °F.
ΔP = Pressure drop through heat exchanger, ft.
SHL = System head loss, ft. (System head loss is based on the heater and tank placed no more than 5 feet apart and 50 feet equivalent length
of tubing and fittings.)
gpm = Gallons per minute, flow rate.
MTS = Minimum tubing size.
*Must utilize optional cupro-nickel tubes.
**With Hard Water (16-25 grains per gallon), the operating control must be set no higher than 130°F for scale free operation. For operating tem-
peratures above 130°F, a water softener must be utilized.
Model
No.
Input
MBTUH
Output
MBTUH
Soft (0–4 grains per gallon) Medium (5–15 grains per gallon) Hard* (16–25** grains per gallon)
ΔT gpm ΔP MTS SHL ΔT gpm ΔP MTS SHL ΔT gpm ΔP MTS SHL
HD101 100 85 9 20 1.8 1-1/2 3.8 7 26 3.0 1-1/2 6.3 4 45 9.2 1-1/2 18.0
HD151 150 128 13 20 1.8 1-1/2 3.8 10 26 3.1 1-1/2 6.3 6 45 9.2 1-1/2 18.1
HD201 199 169 17 20 1.9 1-1/2 3.9 13 26 3.2 1-1/2 6.4 8 45 9.4 1-1/2 18.2
HD251 250 213 21 20 1.9 1-1/2 3.9 16 26 3.2 1-1/2 6.5 9 45 9.6 1-1/2 18.5
HD301 299 254 25 20 1.9 1-1/2 3.9 20 26 3.2 1-1/2 6.5 11 45 9.8 1-1/2 18.7
HD401 399 339 34 20 2.0 1-1/2 4.0 26 26 3.3 1-1/2 6.6 15 45 10.3 1-1/2 19.1
Piping—Heating Boilers
All high points should be vented. Purge valves and a
bypass valve should be installed. A boiler installed
above radiation level must be provided with a low
water cut-off device. The boiler, when used in connec-
tion with a refrigeration system, must be installed so
the chilled medium is piped in parallel with the boiler
with appropriate valves to prevent the chilled medium
from entering the boiler.
The boiler piping system of a hot water heating boiler
connected to heating coils located in air handling units
where they may be exposed to circulating refrigerated
air, must be equipped with flow control valves or other
automatic means to prevent gravity circulation of the
boiler water during the cooling cycle. It is highly recom-
mended that the piping be insulated.
Air-Separation/Expansion Tank
All boilers should be equipped with a properly sized
expansion tank and air separator fitting as shown in
the piping diagrams (Fig. 10–12).
Three-Way Valves
Valves designed to blend water temperatures or
reduce water circulation through the boiler should not
be used. Raypak boilers are high recovery low mass
boilers not subject to thermal shock. Raypak offers a
full line of electric sequencers that produce direct reset
of boiler water temperature. Refer to the Controls
Section in our Complete Catalog.
Domestic Hot Water Piping
When designing the water piping system for domestic
water applications, water hardness should be consid-
ered. Table E indicates the suggested flow rates for
soft, medium and hard water. Hardness is specified as
grains per gallon.