Recirc Pump with Tempering Valve

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John Gayewski

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Wow. Thanks for all the responses. However, I think I didn't make myself clear as to what was being installed and/or asked.
Watts (and Grundfros) make a recirc pump that typically mounts to the hot outlet on top of the water heater. The pump has a clock/timer that tells the circ to move water at the set times, usually from 6am to 9am and sometimes at night or whatever the customer desires to meet their instant hot water needs.
A manifold is also installed under the farthest sink that will move a miniscule amount of hot water into the cold line when the pump is running. There is NO actual separate recirculation line on the system.
See: http://media.wattswater.com/IOM-WQ-500800.pdf
I've installed several of these systems over the years and they work quite well to get hot water quickly to the farthest fixture from the water heater. They also help in the winter with problem water lines that typically freeze inside walls, as the water is constantly moving (if the timer is set as such during the cold months).
If a tempering valve was to be put on the system, would it go before or after the recirc pump?
PS- Terry - thank you for the idea of the Grundfros Aquastat Clip. Tonight I just came from a job that does have the separate recirc line and pump that was wired to run 24/7. I indicated to the new customer that perhaps this is why he keeps getting pin holes in his hot and recirc lines. I was going to pick up an aquastat and well, etc tomorrow and install it for him, but this will save him money and me time so I can help other customers. Thank you as always. Bill
A tempering valve mixes hot and cold water. If you fill the cold side with hot what will the mixing valve do?

What is the purpose of the mixing valve? Is it to make more capacity for the heater? Or is this a boiler system that uses a mixing valve for saftey?

Without a dedicated recirc there is a scald danger whether you have a mixing valve or not.
 

John Gayewski

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I like the $38 dollar part wired to the pump. It's what everyone does in Seattle.

But yes, sell more hardware to customers that have been living in their homes for 15 years. Rip those walls open and change out shower valves. It's only money.

The reasons for adding a tempering valve to a water heater is to increase the amount of heated water, in this case so that dad could shower in the morning.

You could just turn the thermostat up, but then you're scalding people. This the temper valve is a safety device too.

They don't want to wait for heated water to arrive at the far end of the home. They typically already have working recirc pumps in place.

So how to have more heated water, be safe, and not wait for it.
Add the tempering valve and the aquastat. All of this is done at the water heater, a very simple add-on. It makes people happy.
This can be a scald hazzard if the heater is turned above 120. I don't know what else to say about it. Other than we disagree.
 

BILLIARD

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A tempering valve mixes hot and cold water. If you fill the cold side with hot what will the mixing valve do?

What is the purpose of the mixing valve? Is it to make more capacity for the heater? Or is this a boiler system that uses a mixing valve for saftey?

Without a dedicated recirc there is a scald danger whether you have a mixing valve or not.
Hi John, I understand your point but keep in mind that at the water heater the cold side never gets hot. Its still "cold" or room temperature at worst. Never hot. The manifold under the farthest sink basically has a pin-head hole in it that moves a very small amount of hot water into the cold line at the sink. The worst problem I've encountered (from my own wife) is that when she turns on the cold side of the faucet its not "cold" immediately, its warm for a few seconds until the cold water gets back to that faucet.
The beauty of the timer is you can have the pump come on and off every 15 minutes thereby virtually eliminating those "issues".
The reason for the mixing valve in this case is the customer indicates his indirect water heater doesn't give him consistently hot water. If we boost up the temp in the heater and set the mixing valve to a desired temperature, he'll be a happy camper - AND get instantaneous hot water to boot!
 
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John Gayewski

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Hi John, I understand your point but keep in mind that at the water heater the cold side never gets hot. Its still "cold" or room temperature at worst. Never hot. The manifold under the farthest sink basically has a pin-head hole in it that moves a very small amount of hot water into the cold line at the sink. The worst problem I've encountered (from my own wife) is that when she turns on the cold side of the faucet its not "cold" immediately, its warm for a few seconds until the cold water gets back to that faucet.
The beauty of the timer is you can have the pump come on and off every 10 minutes thereby virtually eliminating those "issues".
The reason for the mixing valve in this case is the customer indicates his indirect water heater doesn't give him consistently hot water. If we boost up the temp in the heater and set the mixing valve to a desired temperature, he;ll be a happy camper - AND get instantaneous hot water to boot!
Most indirect heaters have a tempering valve on them. Is that the case here? If so you need to find out what kind and it's perameters. If what your saying is the case "that the pump doesn't move much water" then the tempering valve may not work as intended. If your shopping for a mixing valve I suggest you call Caleffi (not sure on that spelling) they have a very good technical team based in the US that will guide you to exactly the valve you need.

I know these systems and have worked on them. They do in fact fill the cold water side with extremely hot water and can cause issues. I agree that a timer would/could cure that, but then your dealing with creating a legionella breeding ground in the cold water line.

As long as you have the components worked out and are confident you have a good balance then more power to you. But you should proceed with specific components that will work as intended.
 

BILLIARD

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Most indirect heaters have a tempering valve on them. Is that the case here? If so you need to find out what kind and it's perameters. If what your saying is the case "that the pump doesn't move much water" then the tempering valve may not work as intended. If your shopping for a mixing valve I suggest you call Caleffi (not sure on that spelling) they have a very good technical team based in the US that will guide you to exactly the valve you need.

I know these systems and have worked on them. They do in fact fill the cold water side with extremely hot water and can cause issues. I agree that a timer would/could cure that, but then your dealing with creating a legionella breeding ground in the cold water line.

As long as you have the components worked out and are confident you have a good balance then more power to you. But you should proceed with specific components that will work as intended.
I don't see too many ID heaters here with tempering valves installed. They are required now on new installations. On existing systems I've installed them for the sole purpose of getting more hot water from the existing water heater and/or consistent hot water temperature out of the water heater. I have Caleffi valves in stock and waiting to be installed. They're a good product.
Lastly, I doubt the Legionella will ever have a chance to start or flourish in the lines.
 

John Gayewski

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I don't see too many ID heaters here with tempering valves installed. They are required now on new installations. On existing systems I've installed them for the sole purpose of getting more hot water from the existing water heater and/or consistent hot water temperature out of the water heater. I have Caleffi valves in stock and waiting to be installed. They're a good product.
Lastly, I doubt the Legionella will ever have a chance to start or flourish in the lines.
A recirculation system will give you more consistent temps, but a dedicated system is the perfered way to go.

Read up on legionella and the temps they thrive in. It's already in the cold lines heating them up just fires them up and can cause proliferation.
 

wwhitney

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This can be a scald hazzard if the heater is turned above 120. I don't know what else to say about it. Other than we disagree.
So, the product the OP linked to consists of a pump with optional timer control, and a temperature sensitive bypass valve installed at the far fixture. The specs say the hot to cold bypass opens below 98F and closes above 98F.

I infer that the the pump is one that can handle running indefinitely under no flow conditions (or it has some sort of built-in shutoff when the outlet pressure is sufficiently higher than the inlet pressure). Then when the bypass valve opens it can pump (presumably fairly slowly) hot water into the cold side until the bypass closes again.

Thus as far as I can see, as long as the bypass valve is working properly, and there is no other hot to cold bypass in the system, the temperature in the cold line can be no higher than 98F. The hot water side should never get hotter than it would from opening a fixture. The thermally activated bypass valve is effectively acting as an aquastat by controlling when the pump can move water.

Now, if the bypass valve fails open, then the system behavior depends on the mixing valve behavior. If the pump is running constantly (rather than on a timer), and if the mixing valve can't throttle the hot inlet fully closed, and if the heat loss through the loop is zero (which it is not), then the loop (including the cold water return line) would eventually reach full tank temperature.

As to the question in the OP, the pump cited lists a maximum temperature of 140F. So when installed with a mixing valve, the pump should be installed on the mixing valve output, rather than at the water heater. That way it pumps only tempered water. As per the above, a mixing valve that would fully close off the hot side when the cold side reaches the set temperature would provide an additional margin of safety against bypass valve failure. Alternatively an aquastat at the pump, set to a higher temperature than the mixing valve set temperature, would provide another fail safe.

Caveat: I have no direct professional experience with any of the above.

Cheers, Wayne
 

BILLIARD

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So, the product the OP linked to consists of a pump with optional timer control, and a temperature sensitive bypass valve installed at the far fixture. The specs say the hot to cold bypass opens below 98F and closes above 98F.

I infer that the the pump is one that can handle running indefinitely under no flow conditions (or it has some sort of built-in shutoff when the outlet pressure is sufficiently higher than the inlet pressure). Then when the bypass valve opens it can pump (presumably fairly slowly) hot water into the cold side until the bypass closes again.

Thus as far as I can see, as long as the bypass valve is working properly, and there is no other hot to cold bypass in the system, the temperature in the cold line can be no higher than 98F. The hot water side should never get hotter than it would from opening a fixture. The thermally activated bypass valve is effectively acting as an aquastat by controlling when the pump can move water.

Now, if the bypass valve fails open, then the system behavior depends on the mixing valve behavior. If the pump is running constantly (rather than on a timer), and if the mixing valve can't throttle the hot inlet fully closed, and if the heat loss through the loop is zero (which it is not), then the loop (including the cold water return line) would eventually reach full tank temperature.

As to the question in the OP, the pump cited lists a maximum temperature of 140F. So when installed with a mixing valve, the pump should be installed on the mixing valve output, rather than at the water heater. That way it pumps only tempered water. As per the above, a mixing valve that would fully close off the hot side when the cold side reaches the set temperature would provide an additional margin of safety against bypass valve failure. Alternatively an aquastat at the pump, set to a higher temperature than the mixing valve set temperature, would provide another fail safe.

Caveat: I have no direct professional experience with any of the above.

Cheers, Wayne
Thank you Wayne
 

DIYinATX

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How does this look for a mixing valve to go before my Watts 500800?

A Honeywell AMX300

I'm a little concerned about this warning though:

This product does not comply with the “Safe Drinking Water Act,” which requires that products meet low-lead standards in order to be used in systems providing water for human consumption (drinking or cooking). This item is for non-potable (non-human consumption) water applications only.

I do use my water line for drinking water.
Untitled.jpg


EDIT:
Some models are apparently lead-free. Such as the AMX300TLF that I bought.
 
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DIYinATX

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I went ahead and ordered the Honeywell AMX300 mixing valve and the L6006C1018 Aquastatic controller.
I'll post back if it causes any issues with my Watts 500800 recirculating pump.

Recirculation Loop
The purpose of a recirculation loop is to supply immediate
tempered water to all hot water fixtures. This helps conserve
water. In the recirculation loop, the hot water supply returns
from the fixture furthest from the heating source and is
connected to the AMX300 Mixing Valve recirculation port
(marked "R" on the valve body) and the cold supply line of the
water heater.
The AMX300 Mixing Valve allows easy recirculation
connection through the integrated recirculation port. A
temperature-controlled circulating pump is required to move
the tempered water through the recirculation loop. The
Honeywell L6006C1018 Aquastat® Controller is the
recommended temperature control device for the circulator.
The Honeywell Aquastat Controller should be set 5° to 10° F
(3° to 5° C) below the controlled mixed water outlet
temperature.

 
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