LAARS Mighty Therm LO-NOx PW (Sizes 500-1825) - Install and Operating Manual - Manual (Page 14)

LAARS HEATING SYSTEMS Page 14
3.3.5 Water Pressure
It is very important that water pressure in the
system be maintained above 30 psi. If the system
pressure should drop below this, the vapor pressure of
water in the suction side of the pump can cause
hammer and cavitation in the pump and damage the
heater through lack of water circulation.
For protection against excessive pressure the
water heater is equipped with a pressure relief valve.
When the water heater is connected to a separate
storage vessel, a temperature and pressure relief valve
must be installed on the storage vessel. The
temperature and pressure relief valve must be design-
certified in accordance with the requirements for
Relief Valves and Automatic Gas Shutoff Devices for
Hot Water Supply Systems, ANSI Z21.22. (in Canada,
in accordance with the requirements for the Standard
for Temperature and Pressure Relief Valves and
Vacuum Relief Valves, CAN1-4.4).
The temperature and pressure relief valve must
have a BTU/h (kW/h) capacity rating that is greater
than the BTU/h (kW/h) input of the water heater. The
temperature and pressure relief valve must be marked
with a maximum working pressure not to exceed the
maximum working pressure shown on the rating plate
of the water heater, or the maximum working pressure
of the separate storage vessel, whichever is the lower
pressure. The temperature and pressure relief valve
must have a maximum working temperature not to
exceed 210°F (99°C).
Do not place any shutoff valves between the
temperature and pressure relief valve and the storage
vessel.
The relief valves discharge water in large
quantities should circumstances demand.
3.3.6 Tank Installation
1. Be sure the floor is waterproof and structurally
capable of supporting the tank when it is filled
with water.
2. The tank should be placed so that manholes,
inspection covers, nameplates and drain valves
are accessible.
3. Be sure the tank is suitable for the water in the
system. Some water is corrosive and requires a
protected tank with a special lining.
4. If the tank is glass-lined, it should be equipped
with a suitable magnesium anode. It is good
practice to replace the anode when it is
approximately 50% used. The factory warranty
on a glass-lined tank, if provided, will be void if
a satisfactory anode is not in place at the time of
a failure or if it is consumed by cathodic action.
5. Make sure the tank connections in the heater-
tank circulating loop are the proper size as listed
in Section 3.3.4. If tappings are smaller than the
recommended pipe size, a larger pump may be
required. Consult the factory if in doubt.
6. Install a pipe in the tank drain fitting that goes to
a floor sink, and install a drain valve. If a floor
sink is not available, install a hose bib.
3.3.7 Two-Temperature System
See Figures 15 and 16 for piping schematics.
This system is designed to maintain the tempered
water circulating loop at the desired temperature
Legend
Check Valve
Tempering Valve
Venturi (Suction) Tee
Throttling Valves / Service Valves
Figure 15. Two Temperature Hot Water Supply system with Horizontal Tank.