Mighty Therm VW - PW Volume Water Heaters
Page 11
2F-4. Water Hardness
Consider the water hardness when selecting a
pump for the heater (see Table 3). Hard water needs a
pump which can provide high flow to prevent scaling,
while soft water needs low flow to prevent erosion.
34.
Carefully slip a hand inside to make sure there
are no gaps between the heat exchanger and the
flue collector.
35.
Check to make sure the wiring is not pinched
against sharp edges, or resting on the collector
assembly.
36.
Replace the two flue collector holddown clamps.
37.
Replace the top assembly and fasten it with the
hex-head screws.
38.
Replace the front cover.
39.
Reinstall the vent cap or drafthood if one was
removed.
40.
On indoor installations (sizes 175-250), insert the
draft hood switch plug into the receptacle on the
left side of the heater.
2F-2. Water Chemistry
Laars equipment is designed to be used in a
variety of water conditions. With the proper pump, the
water velocity in the heat exchanger tubes is kept high
enough to prevent scaling from hard water, yet low
enough to avoid erosion by soft water.
NOTE: It is possible to have hard and soft water
in the same city. Check with the local water
companies.
If an installer sees damage to any water handling
equipment at the installation site, it should be repaired
as soon as possible to help reduce maintenance costs.
If there is erosion, resize the pump to reduce water
velocity before the tube ruptures. If scaling is bad, set
up a heat exchanger tube-cleaning maintenance
schedule to prevent heat exchanger tube cracking and
wear. Not fixing the condition will mean serious
damage to the heater and the water system.
NOTES:
•
In areas where the water supply is soft or
corrosive, the heater must have cupronickel tubes
in the heat exchanger.
•
Laars does not warrant heat exchangers damaged
by scaling, corrosion, or erosion.
2F-3. Freeze Protection
Although VW-PW heaters are design certified by
the International Approval Services (IAS) (formerly
American Gas Association [AGA] and Canadian Gas
Association [CGA]) for outdoor installations, such
installations are not recommended in areas subject to
freezing temperatures unless proper precautions are
taken. Consult the local factory representative or Laars
for additional information.
Hardness
Grains per
Parts
Category
Gallon
per Million
Soft
1 through 7.5
17 through 128
Normal
7.6 through 17
129 through 291
Hard
Over 17
Over 291
Table 3. Water Hardness.
2F-5. Pump Requirements
The VW heater does not have a factory installed
pump (see Table 4 for pump performance require-
ments). The PW heater does have a factory installed
pump which is for heater-to-tank circulation only.
VW and PW heaters are not designed for applica-
tions where the temperature of the water flowing
through the heater remains below the dew point, 110°F
(43°C).
The factory provided pump on the PW heaters,
and the pumps recommended for field installation on
VW heaters, are sized to provide proper circulation
through the heater, and through the heater-to-tank
circulation loop (see Figures 20 through 22).
If the heater-to-tank circulation loop does not
contain more than 6 elbows or 30 feet (9.1 m) of pipe,
the minimum pipe fitting should be 1-1/2 inches (38
mm). If the loop does contain more than 6 elbows or
30 feet (9.1 m) of pipe, the minimum size should be
2 inches (51 mm).
2F-6. Pressure Buildup in Water System
The water utility supply meter may contain a
check valve, back flow preventer, or water pressure
reducing valve that will create a closed water supply
system. Contact the water supplier or local plumbing
inspector on how to control this situation.
During the heating cycle of the heater, the water
expands creating a pressure buildup in the water
system. The pressure relief valve may discharge hot
water under these conditions, causing a loss/waste of
energy and a buildup of lime on the relief valve seat.
NOTE: Do not plug the relief valve.
There are two methods to prevent the relief valve
from discharging hot water in a closed water system:
1.
Install a pressure relief valve on the cold water
supply line. Make sure that the discharge of this
valve is directed to an open drain and protected
from freezing.
2.
Install a properly sized thermal expansion tank
on the cold water supply line.
