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Why air
vent?
Recirculation pumps can cause air bubbles as the impeller spins.
Air bubbles cause noise in pump and plumbing pipes.
Air bubbles can cause water to stop circulating, and cause overheated
pump.
Air vent releases air trapped in the water line. Air vent has 1/4" pipe
thread/ install ordinary plumbing tee and use
1/4" reducing bushing / use teflon tape on 1/4" pipe thread
Install at highest point in recirculation loop.
Buy
air vent:
Air vent/
Float vent
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Installed on cold water line
Expansion
tanks at Amazon
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Why expansion
tank on
cold water line?
Expansion tank is installed on the incoming cold water line.
In some tankless recirculation drawings, expansion tank is
located on hot water line of recirculation loop.
Generally, however, the recirculation loop will not need expansion tank.
However, if the small water heater is set to very high temperatures
(135+), then it can cause thermal expansion on the 'closed'
recirculation loop.
Remember, the recirculation loop is 'closed' because of the check valve
between tankless and recirculation loop. Any closed system is risk for
thermal expansion, especially if water heater is set for very high
temperature. Tank temperature for the 20 gallon should be 120°F or less
since typical hand wash would be 110°. Temperatures over 140°F pose
serious risk of scald and should never be present in a residential
water heating system unless sterilization is needed. Use a mixing valve
and separate hot water lines for safety.
Most cases, the expansion tank on cold water line will ensure that
plumbing lines are not vulnerable to thermal expansion, or high
pressure that can cause damage to pipes and fixtures and water heaters.
Buy:
Expansion
tanks at Amazon
Resources
Thermal expansion and closed system
Expansion Tank Installation pdf
Advantages mixing valve |
Closed
system: the need for
expansion tank.
-Water expands as it is heated. When a water heater is running, the
'thermal expansion causes the volume of water to
increase, causing increase in water pressure, putting pressure on the
tank, pipes, and fittings.
Resources
Thermal expansion and closed system
-'In an open system the increase in water pressure flows back
into the city water supply.' In a water well service,
the pressure goes back into the pressure tank located at well.
-'In
a closed system, the increase in pressure is blocked from flowing back
into city water supply. The resulting thermal expansion can
create a
rapid and dangerous pressure increase in the water heater and the
system piping.' Symptoms include release of water from TP valve,
bulging
water heater or pipes, and premature tank failure.
Correctly sized expansion tank on incoming COLD water line solves
problem of thermal expansion.
-Your
water system probably does not have a pressure issue unless you have a
pressure reducing valve on the incoming cold water line, high incoming
water pressure over 80 psi from the city supply (put pressure gauge on
outdoor spigot to check), a check valve on incoming cold water supply,
or very high thermostat setting on water heater.
-Often local codes require an expansion tank as nod to the plumbing
industry and not particularly because of need.
With
the direct return line installation, do
the Check valves on the Hot pipes of recirculating system cause a
'closed system?'
I don't know for certain. But let's look at some factors:
1) The recirculation check valve from tankless is open when the
tankless
is supplying hot water to end user .... so we know for certain the
expansion tank will protect
during tankless operation.
2)
Expansion tanks are typically installed on incoming cold water supply
line, but with the small tank, the incoming 'cold water supply line' is
cut off by a check valve when the tankless is off and recirculating
pump is operating, so
technically this could cause a closed system.
3) There is no way to
know if the check valves will cause a pressure problem until the small
tank is in
operation, and then the symptom would be discharging TP valve on small
tank, or explosion of hot water when tap is turned on.
4) The small tank might not cause a lot of expansion. If the system has
direct return line,
the thermostat on small tank does not have to be set same temperature
as tankless. Since the average
hot temperature at tap is 104°, the small tank thermostat can be set at
110° (to compensate for heat loss in pipe) ... and the lack of very hot
water would
minimize (or eliminate) thermal expansion... the more the circulating
pump runs the more the heat would dissipate, and the less expansion on
line.
5) Most but not all
tankless recirculating diagrams show the check valves. The newer
diagrams all show the check valves for the direct return line
installation.
6) In one older tankless recirculation drawing, expansion tank is
located on hot water line of recirculation loop. Resource: Nortiz .pdf
However every new drawing available from manufacturer shows the
expansion tank on incoming cold water line, same as illustrations on
this webpage.
Since the .pdf
files posted on this webpage predominately show the check valves, and
show a single expansion tank on incoming cold water line, my best guess
is that thermal expansion on the recirculation loop is not an issue. |
Temporary pressure gauge |
Avoid water
pressure
over 80psi
Save
cost of water heater
replacement and plumbing repairs
Resources
Water
pressure:
Pressure over 80 psi can damage
water
heater
High pressure will also shorten life of plumbing fixtures, and cause
washing machine hoses to rupture, etc.
Symptoms: TP valve goes bad frequently. Cause: Closed system because of
check valve or faulty pressure valve, or community water problem or
water well pressure set too high.
Test and diagnose TP valve problems
Connect pressure gauge to water heater
drain
valve to accurately check
pressure.
Install pressure reducing
valve. Replace check valve. People with water well > turn down
pressure on
water well > save both hot and cold water, save
electricity, and well equipment lasts longer.
Buy:
Water
pressure gauge
Pressure
reducing valve
Temperature-pressure
gauge
Pressure
gages at Amazon
Resources
How to test pressure
Test and diagnose TP valve problems |
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Buy:
Replacement
crossover valve
Watts sensor valve kit
Applies to Taco, Grundfos and Watts. Does not apply to Laing
Crossover
valve installs under sink, and allows hot water to circulate from hot
side to cold side. Purpose of crossover valve: When recirculation pump
is ON, the crossover valve opens and lets hot water circulate back to
water heater through the cold water line. Immediate hot water is
available at the faucet. When you turn on cold water at the faucet, the
crossover valve closes, allowing cold water to enter
the
faucet.
Note: Cold is not available immediately
at the faucet.
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