Recovery is the amount of water per hour
the heater can raise the temperature of by 100
degrees.
The reason these numbers are important is
that many people believe that all 30 gallon
water heaters produce the same amount of hot
water; however there is a HUGE difference in
the amount they actually produce.
When sizing indirect water heaters, it’s
important to make sure that you have the right
Figure 9
circulator to enable the the tank to supply the
desired demands of hot water. The chart for the
SSU-45, which is a 45 gallon indirect tank,
shows that the required minimum flow rate
through the coil in the indirect tank is 10
gallons per minute. See Figure 9.
With that flow rate, the pressure drop
through the coil alone is 7.9 foot of head.
Add the associated piping to and from the
tank and the boiler to this number to get
the proper circulator size.
If there is 30’ feet of 1” copper to the
tank, the pressure drop for that would be:
30 x 1.5 = 45
40 National Oilheat Research Alliance
Pipe Sizing
Model
Dimensions
Capacity
Heat Exch.
Surface
Recomm.
Flow Rate
Pressure Drop
(Feet)
This was discussed in Chapter 3 on page 27,
under section 'Head" explaining Head Pressure
Drop.
Thus, 45 x .04 =1.8 foot of head loss. Add
that to 7.9 for the coil and you have 9.7 foot of
head. So your circulator demands just for the
indirect tank would be 10 gallons per minute
with 9.7 foot of head loss. Use the performance
curve to select the correct circulator. Figure 10.
Unfortunately, none of these circulators are
180° Boiler
Water First
Hour Ratings*
(in Gallons)
200° Boiler Water
First Hour
Ratings*
(in Gallons)
Ht. Dia. (Sq. Ft.) 115°F 140°F 115°F 140°F
SSU-20 27" 19¼" 20 15 8 6.0 121 168 136 185
SSU-30 39½" 19¼" 30 15 8 6.0 154 212 172 234
SSU-30LB 29½" 23¼" 30 15 8 6.0 169 234 189. 257
SSU-45 52½" 19¼" 45 20 10 7.9 212 292 237 322
SSU-60 52½" 23¼" 60 20 10 7.9 266 370 298 40
SSU- 80 72" 23¼" 80 34 12 9.1 9.1 330 440 370 503
SSU-119 73½" 27" 119 34 14 11.3 423 564 474 645
DOE test method based on 90°F temperature rise, 50°/140°W/ boiler water at 180°F
Recommended flow rate: 10 GPM Coil head loss 7.9'
able to meet the required
performance. So, you
will need to use a multispeed
circulator. An improperly
sized circulator
will prevent the water
heater from delivering
the gallons described in
its specification sheet.
See Figure 11 on following
page.
This circulator, set on
high speed, does meet
the requirements.
In additIon to sizing
the circulator correctly, to ensure the correct
amount of hot water is delivered, the boiler
Figure 10