LAARS Mighty Therm IW (Sizes 500-1825) - Installation, Operation and Maintenance Instructions - Manual (Page 16)

LAARS Heating Systems
Page 16
2I. 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. If for any
reason the water supply is turned off temporarily to
service a piece of equipment, the manual gas valve
on the Model IW should be closed until the water
pressure has been restored and the lines bled of
accumulated air. If the heater fails to fire when it is
turned back on, it may be airlocked. To eliminate the
airlock, open the pressure relief valve and allow air to
bleed out until water flows. As soon as full circulation
is resumed, the entrained air will be carried out
through the hot water faucets.
2J. 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 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 2H. 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.
7. Hot water tanks in an existing installation are
likely to have a deposit of silt on the bottom.
Therefore, it is important to extend the pump
suction pipe in the tank to a position near the top.
Pipe the return from the heater to the bottom of
the tank.
2K. Two-Temperature System
See Figures 16 and 17 for piping schematics.
This system is designed to maintain the tempered
water circulating loop at the desired temperature
during idle periods as well as when there is a demand
for hot water. It is recommended for general purpose
water supply including shower and bathing
applications. Water at 180°F is available directly from
the tank.
SECTION 3.
Operation
3A. Controls - General
1. Electronic Ignition Controls:
a. Intermittent Ignition:
Pilots are automatically lit when the
operating aquastat calls for heat (System #9
and #4)
The unit performs its own safety check and
opens the main valves only after the pilot is
Flow Head* Temp. Rise
Water Rate Loss Across
Model Category (GPM) (ft.) Heater, (°F)
Soft 45 5.0 17
500 Normal 68 9.9 11
Hard 90 15.7 8
Soft 45 5.1 20
600 Normal 68 10.0 14
Hard 90 15.9 10
Soft 45 5.3 24
715 Normal 68 11.0 16
Hard 90 17.8 12
Soft 45 5.4 30
850 Normal 68 11.1 20
Hard 90 18.1 15
Soft 45 3.9 35
1010 Normal 68 7.5 23
Hard 90 11.7 18
Soft** 68 7.8 27
1200 Normal 68 7.8 27
Hard 90 12.2 21
Soft** 68 8.1 32
1430 Normal 68 8.1 32
Hard 90 12.6 24
Soft** 68 8.3 37
1670 Normal 68 8.3 37
Hard 90 13.0 28
Soft** 90 13.5 30
1825 Normal** 90 13.5 30
Hard 90 13.5 30
Water Category Grain Hardness per Gal.
Soft 1 through 7.5
Normal 7.6 through 17
Hard
Over 17
* Pressure drop includes loss through 30 feet of pipe and normal fittings when
heater is installed with storage tank. Pipe and fittings are assumed to be 2" on
Models (500-850) and 2 1/2" on Models (1010-1825)
** To prevent erosion, these models must be ordered with cupro-nickel heat
exchanger tubes.
Table 4. Pump Performance Requirements.