LAARS Mighty Therm LO-NOx PH (Sizes 250/400) - Install and Operating Manual - Manual (Page 13)

Mighty Therm LO-NOx Hydronic Boiler Page 13
Temperature Rise in °F °C
20°F 11°C 25°F 14°C 30°F 17°C 35°F 19°C
Size GPM H/L* L/s GPM H/L* L/s GPM H/L* L/s GPM H/L* L/s
ft m ft m ft m ft m
250 20 2.1 1.26 0.6 16 1.00 1.2 0.4 13 0.82 0.8 0.2 11 0.69 0.6 0.2
400 31 1.96 5.2 1.6 25 1.58 3.4 1.0 21 1.32 2.3 0.7 18 1.13 1.7 0.5
Water Flow - GPM or L/s: Gallons per minute or Liters per second.
*Pressure drop (head loss) through the boiler, expressed in feet or meters of water (H
2
0).
Figure 23. Multiple Boilers, Low Temperature System.
must be increased by changing the piping or pump
size.
2.6.3 Variable Water Flow Systems
There can be reduced water flow through the
boiler in heating systems using zone valves, zone
pumps or 3-way valves. This can result in a high
temperature rise across the boiler. Laars recommends
primary-secondary pumping for all variable flow
systems. The boiler pump in a primary-secondary
system maintains constant flow through the boiler even
though the system flow is variable. In a primary-
secondary system the pressure drop of the boiler is not
added to the system (see Figures 22, 23 and 24).
2.6.4 System Pressure Requirements
The HH, PH boilers are designed to operate on
closed, pressurized systems. A minimum of 12 psi
(82.7kPa) should be maintained on the system where
boiler supply water temperatures are 200°F (93°C) or
less. If higher temperatures are required, the minimum
system pressure should be at least 15 psi (103.4 kPa)
above the water vapor pressure corresponding to the
elevated water temperature.
Do not use the HH, PH boilers to operate on
open, pressurized systems unless the supply water
temperatures are kept below 180°F (82°C), and a
minimum of 5 psi (34.5 kPa) static head is maintained
at the boiler.
Table 3. Temperature Rise.
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