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Tankless recirculation system

Tankless recirculation system
Larger image
Best design

Tankless manufacturers suggest installing 20 gallon secondary tank heater to ensure hot water arrives at destination.

Three Illustrations show:
Top two: direct return line/  
Bottom: without direct return line
Direct return line is better installation

Water must circulate through small water heater to ensure there is hot water in the recirculation loop. Reason: small pump cannot activate tankless burner or element

Check valve can be added on direct return hot water line as shown
Add check valve to cold water line for loop without direct return

System can have faucets that are not connected to recirculation loop... add a small 3 gallon under counter water heater to this faucet

Water flow causes pressure.
The small pump creates pressure. The check valve between tankless and recirculation loop (on top illustration) will keep recirculation pump from pushing water into tankless. So the pump is just recirculating hot water in the loop.
Using hot water during a shower also causes pressure... and when tankless is being operated, the other check valve will keep water from being pushed into small tank and backwards through recirculation loop.

It's also true that water flow can cause suction.
For example if end of garden hose is left inside a pond after filling pond.... and you turn on water tap inside house... the pull of water can draw water from the pond if the outdoor spigot has a small seep.
For example if end of garden hose is left inside a pond after filling pond.... and you turn on water tap inside house... the pull of water can draw water from the pond if the outdoor spigot has a small seep.
To prevent this problem, add anti-siphon connection on outdoor spigots.

However, in the case of recirculation pumps, the water flow is not very strong, and the system is a closed loop... a closed loop is not drawing water like an open spigot... and the 1/25 Hp recirculation pump is not moving the water very fast, so drawing cold water into the loop is not an issue.

Resources:
Compare small water heaters
Rheem-tankless-recirculation-system2.pdf
Rheem-tankless-recirculation-system.pdf
Using-point-of-use-recirculation.pdf
Tankless-recirculation.pdf
Nortiz-tankless-recirculation-diagram.pdf
Water heater valves

Which 20 gallon water heater

For whole house, you need water heater with 3/4" pipe fittings
1/2" pipe is too small for household size recirculation system
1/2" is for single faucet
Resources:
Compare small water heaters

Which recirculation pump?

Each plumbing system is different... distance, diameter of pipe, condition of pipe, number of elbows, ...  effect flow of water.
Resources:
How-to-choose-proper-circulator-pump.pdf
Compare recirculation pumps

Why isn't there a stronger recirculation pump?

Probably faster pump on small residential pipe would just cause water bubbles, and no water movement, and then resistance would overheat pump?
Tankless recirculation system
Larger image
Connect Hot from tankless to cold water inlet on small hot water heater
Tankless recirculation system
Larger image
No return line/ not best design
Check valve
Swing check valve

Swing check valve

Look at directional arrow located on check valve
Make sure arrow is same direction as flow of water
Buy:
Swing check valve at Amazon

Low pressure

Does check valve reduce pressure?
Check valve would have minimal affect on water pressure.
Unless check valve is stuck with sediment build-up, or lost its seal so water is flowing backwards.

More resources on low pressure
http://waterheatertimer.org/Low-hot-water-pressure.html
http://waterheatertimer.org/Crossover.html

Swing check valve

Check valve that swings open when water passes one direction.
And swings closed when water tries to pass other direction.
One way valve: Lets water pass one direction, but not other direction

Why is check valve important?

With some installations, recirculation system loop can draw cold water into hot pipe causing cold flashes during shower. This occurs during heavy use periods.
Or with the direct return loop type installation, the recirculation loop can lose pressure or lose recirculation effect when cold or hot is drawn elsewhere in the plumbing system.

If check valve is used elsewhere in plumbing system, and check valve goes bad, it can cause crossover, where cold enters hot pipe and hot water never arrives at faucet:
Or a bad check valve can cause high or low pressure
Swimming pool, or outdoor ponds: If water hose is left in pool or pond or puddle of water, then water use inside home can draw this unsanitary water back through water hose and into home water pipes. Install swing check valve. Do not leave hoses on ground. Or in pool.
Buy:
Swing check valve at Amazon

Resources:
Crossover
Low hot water pressure

Why air vent?

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
Often, recirculation pumps cause air bubbles as the impeller spins inside the water pipe
Air bubbles can cause pump, or plumbing pipes to make noise
Air bubbles can cause water to stop circulating
Buy air vent:
Air vent/ Float vent
expansion tank
Installed on cold water line
Expansion tanks at Amazon

expansion tank

Why expansion tank on cold water line?

Expansion tank can be installed anywhere on the cold water line
In some tankless recirculation drawings, they show expansion tank located on hot water line of recirculation loop
Generally, however, the recirculation loop will not need expansion tank
However, it the small water heater is set to very high temperatures (135+), then this 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
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
Read about expansion tanks and closed system
Expansion Tank Installation pdf

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 BTG 100 pressure gauge to water heater drain valve to 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 gauges
Temperature-pressure gauge
Pressure gages at Amazon

Resources:
How to test pressure
Test and diagnose TP valve problems


Crossover valve
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.
Taco recirculation systems  vv
Taco
Install pump at water heater
Install crossover under sink
Choose timed or thermostat operation
Plug into 120V outlet
1 year warranty with receipt
Buy:
Taco recirculation systems
Resource:
General Taco manual
General manual
Figure flow rates for recirculation pumps
Basic pump science/ pdf

Read more about recirculation
Grundfos recirculation systems
Grundfos
Install pump at water heater
Illustration shows typical water heater model
Install crossover under sink
Choose timed or thermostat operation
Plug into 120V outlet/ draws 1/4 amp
2 year warranty with receipt
Buy:
Grundfos recirculation systems at Amazon
Replacement crossover valve
Clip-on thermostat control
Cast iron flange set for flanged pumps
Resource:
General Grundfos product manual
Can use on tankless 0-9 GPM
How to choose proper circulator pump
watts recirculation systems
Watts
Install pump at water heater
Install crossover under sink
Choose timed or thermostat operation
Plug into 120V outlet
1 year warranty with receipt
Buy:
Watts recirculation systems
Replacement crossover valve
Watts sensor valve kit
Resource:
Watts recirculation system manual
Do not install on tankless
Tankless require .5 GPM
Laing recirculation systems
Laing Thermotech
Install under sink/ buil- in crossover valve
Pump and crossover built into same unit
Choose timed or thermostat operation
Plug into 120V outlet
2 year warranty with receipt
Buy:
Laing recirculation systems

Resource:
Autocurc manual
ACT 909 tankless recirculation pump manual
E10 autocirc manual
Laing thermotech

Read more about recirculation
Reliance water heater
Reliance
6-10 gallon
Side connections/
6 year warranty
Buy
Reliance water heaters
12-3 extension cords
12-3 southwire cable
Resources
Reliance manual
State manual
American tiny titan water heater
American
6-12 gal
Top connections/
6 year warranty
Buy
American tiny at Amazon
12-3 extension cords
12-3 southwire cable
Resource:
American manual
State point of use water heater
Rheem
2-6-10-20 gallon
Side connections/
6 year warranty
Buy 
Rheem point of use
12-3 extension cords
12-3 southwire cable
Resource:
Rheem manual
Recirculation pumps for solar claim 50-80 % improved efficiency
http://us.grundfos.com/cases/find-case/Circulator-Pumps.html.html
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