Recirc Pump with Tempering Valve

[BILLIARD]

A customer has a large house and it takes a long time to deliver hot water to the farthest fixture in the house. In the past I have successfully installed the Watts (or Grundfros) Recirc pump system at the water heater. However we also want to install a mixing valve/tempering valve at the water heater.
Typically the recirc pump gets installed on the hot outlet of the heater and a manifold gets installed under the farthest sink from the heater.
Question: Has anyone done this? and if so, successfully? Then where does the recirc pump go in relationship to the tempering valve?
Thank you in advance

 

[Terry]

With a tempering valve in combination with a recirc pump, you will need to add an aquastat.
Grundfos makes one that clips onto the 1/2" return pipe. Without the aquastat, the temperature will continue to climb until the entire loop is as hot as whatever the water heater has been turned up to.

With the aquastat, the pump gets turned off when the recirc line reaches temperature. Customers I've installed these for say that it works well.
It was kind of a disaster without the aquastat. Nobody wants to see their kids dealing with 160 degree water out of their shower heads. The aquastat prevents that.

https://terrylove.com/forums/index.php?threads/honeywell-am-1-thermostatic-mixing-valves-water-heater-tempering.45651/

 

[Sponsor]

 

[wwhitney]

I have no direct experience. But it seems like the only restriction on using a recirc pump with a mixing valve would be that you have to ensure that the returning hot water can go either to the tank or the cold water side of the mixing valve as required. If you set up a system with a dedicated return line so that the return water couldn't make it to the cold water side of the mixing valve, then when recirculating there's no way for the mixing valve to mix in cold water, based on mass balance.

So as far as I can see as long as you satisfy that restriction, you can install the mixing valve and the recirculating system each as usual, and they will interact OK.

Cheers, Wayne

P.S. Plus what Terry said. I'm assuming a recirc system that would just run until you get, say, 120F water at the desired location. And I'm assuming that the mixing valve can deal with mixing, say, 140F tank water with 110F return water to put out 120F water.

 

[wwhitney]

With a tempering valve in combination with a recirc pump, you will need to add an aquastat.
Grundfos makes one that clips onto the 1/2" return pipe. Without the aquastat, the temperature will continue to climb until the entire loop is as hot as whatever the water heater has been turned up to.

In the diagram below (which doesn't show the pump location, but it's between the orange mixed hot water line and the purple return line), I labeled some locations on the cold side. When you had the above problem, did you perhaps have a check valve at 3 and the return line connected at 4? In that configuration the mixing valve can't add cold water to the recirculation loop, as there's no room for more water. So I would expect the recirculation loop to get up to full tank temperature, as you describe.

But as far as I can see, if you put the check valve at, say, 1, and connect the return line anywhere at 2-6, the mixing valve should keep the recirculation loop at the mixing valve set point. That is, I would expect that once the return water temperature hits the mixing valve set point, the mixing valve would close its hot water input, and then there's no recirculation through the tank.

Cheers, Wayne

 

[Terry]

You can try it yourself, but it's also in the manuals for recircs. Mostly it's not real noticeably, people tend to skip over that, but it is in their directions.
Whenever I do recirc with tempering, the aquastat gets added.
It's a $45 part that snaps over the pipe and a quick wiring job to the pump. No more calls about scalding water in showers.
From a legal standpoint, you would open yourself up to lawsuits if you leave it off.

After adding the aquastat, I have happy customers. Lot's of "safe" hot water.

 

[John Gayewski]

Why the tempering valve? Generally when you circulate water you don't use a singular mixing valve. You would mix at the fixture(s) that need protecting. The mixing valve will shut and the pump will need to be off BEFORE that happens. Unless these two are in sync and there's no possibility of the pump being on as the valve shuts which generally isn't practical. Also the pump will need to kick on AFTER the valve opens. If either of these two aren't in sync the pump is toast in short order.

There are mixing valves that have circulation bypasses built in.

What's the exact plan here? Because this would be an irregular situation.

 

[Terry]

It's a normal situation when someone wants more heated water from their tank. Let's pretend you're the dad and the kids and wife have had showers before you had your chance to. You could replace your 50 gallon gas water heater with an 80 gallon tank, but the chimney you have now is only a 3" and not the 4" needed for the 80 gallon. But then the dad calls me up and askes for advice on getting a shower in the morning. Dude, you will want a tempering valve at the water heater that allows you to turn the water heater temperature up all the way, blend that hot water with water from the cold side down to a safe 120 degrees. Your 50 gallon now heats like an 80 gallon. Yahoo!
But wait, you also have a pumped recirc line coming back from your furthest fixture, and if you allow the pump to just keep pumping, eventually the output from the tempering valve becomes as hot as the hot water in the tank. We need a way to turn off the pump when the return line has been heated, we just want to bump the recirc when it cools off and maintain a loop that's heated. It's a $38 dollar part that fixes the problem.
I get a call back from the dad, Geez Terry, you're a genius. Now I get my shower in the morning, and I don't have to wait for hot water either.

1/2" Clip-On Thermostatic Control for Grundfos UP Series Circulators​

 

[John Gayewski]

It's a normal situation when someone wants more heated water from their tank. Let's pretend you're the dad and the kids and wife have had showers before you had your chance to. You could replace your 50 gallon gas water heater with an 80 gallon tank, but the chimney you have now is only a 3" and not the 4" needed for the 80 gallon. But then the dad calls me up and askes for advice on getting a shower in the morning. Dude, you will want a tempering valve at the water heater that allows you to turn the water heater temperature up all the way, blend that hot water with water from the cold side down to a safe 120 degrees. Your 50 gallon now heats like an 80 gallon. Yahoo!
But wait, you also have a pumped recirc line coming back from your furthest fixture, and if you allow the pump to just keep pumping, eventually the output from the tempering valve becomes as hot as the hot water in the tank. We need a way to turn off the pump when the return line has been heated, we just want to bump the recirc when it cools off and maintain a loop that's heated. It's a $38 dollar part that fixes the problem.
I get a call back from the dad, Geez Terry, you're a genius. Now I get my shower in the morning, and I don't have to wait for hot water either.

1/2" Clip-On Thermostatic Control for Grundfos UP Series Circulators​

View attachment 88115

Where are you clipping the aquastat?

The recirc line won't get hot unless the pump runs.

 

[Terry]

Where are you clipping the aquastat?

It clips onto the 1/2" return line to the pump. I open the cover on the pump and wire nut the wires together.

 

[John Gayewski]

It clips onto the 1/2" return line to the pump. I open the cover on the pump and wire nut the wires together.

But that line is cold unless the pump runs, the pump can't run if the valve is shut.

You need to tell the pump that the valve is open

 

[John Gayewski]

You either need a complex control system or a tiny little (?) gallon water heater that can circulate the water in the piping and switch to the mixing valve main water heater secondarily and in series.

But like I said I think there are mixing valves that have a research bypass built in.

 

[Terry]

But that line is cold unless the pump runs

You need to tell the pump that the valve is open

I have installed a lot of these, and they work well. My supplier sells them for that purpose too.
It's a fix that costs me $38.00

Why does this bother you so much that it works?

 

[John Gayewski]

I have installed a lot of these, and they work well. My supplier sells them for that purpose too.
It's a fix that costs me $38.00

Why does this bother you so much that it works?

I'd be happy to look at a diagram but the mixing valve shuts off the hot water to the return before the pump shuts off. With no water going to the pump and the pump running that will ruin a pump. Unless there's some situation I'm unaware of.

 

[Terry]

Wow! The pumps came with the homes. Customers wanted more available hot water and with safe measures.
I installed a tempering valve and the $38 aquastat that have been working for years. It's normal plumbing, not weird plumbing.
Engineers came up with this. And my customers love me for it.
Can't please everyone though.

 

[wwhitney]

Here's an interesting discussion of some of the issues:

Temperature creep in hot water recirculation

We get a lot of tech support calls asking about proper piping of a point-of-distribution master mixi...

www.caleffi.com

One thing I didn't understand in my previous responses was that "most thermostatic mixing valves" do not have 100% close-off on their inlet ports. So if they can't completely cut off the higher temperature tank water, the recirculating loop temp can creep above the mixing valve's set temp.

As Terry suggests, using an aquastat to stop recirculating when the far temperature reaches the set point is one way to stop that temperature creep.

If you do have a mixing valve that will fully shut off the hot side (the above link suggest that digitally controlled ones often do), then I believe the discussion in my post #4 applies.

Cheers, Wayne

 

[John Gayewski]

Wow! The pumps came with the homes. Customers wanted more available hot water and with safe measures.
I installed a tempering valve and the $38 aquastat that have been working for years. It's normal plumbing, not weird plumbing.
Engineers came up with this. And my customers love me for it.
Can't please everyone though.

I can imagine a scenario where what you're talking about works okay. But I can also Imagine a scenario where the pump is either pulling cold water from the fixture or deadheading against the valve in which case the end user might not feel a system that's working improperly. Or even works against the goal.

Either case an engineered system, which I see a a lot of and regularly, doesn't usually look like this. Unless the mixing valve is of a 4-port variety

 

[John Gayewski]

I'm highly distracted right now so my posts are being edited in a little choppy

 

[John Gayewski]

A customer has a large house and it takes a long time to deliver hot water to the farthest fixture in the house. In the past I have successfully installed the Watts (or Grundfros) Recirc pump system at the water heater. However we also want to install a mixing valve/tempering valve at the water heater.
Typically the recirc pump gets installed on the hot outlet of the heater and a manifold gets installed under the farthest sink from the heater.
Question: Has anyone done this? and if so, successfully? Then where does the recirc pump go in relationship to the tempering valve?
Thank you in advance

Whitney posted a link of how to do what you wish. It's similar to being secondary and in series with a small tank like I suggested, but they don't have a tank in there. Those balancing valves direct traffic when the valve closes, and you have to make sure you have the specific right valve for it. There are a lot of different mixing valves out there for all different applications so be aware.

Normally we use mixing valves at the fixtures (Toto makes some good ones with with a one way design incorporated) and a thermostatic shower valve which will let you circulate water at any temp and be fully protected. I'm not sure the Caleffi diagram will do that, but it's a way that they say does work. They know hot water and it's components pretty well there and I might try this setup at one of the houses to see how she does.

 

[Terry]

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.

 

[BILLIARD]

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

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/53315-source/pf-ihwrs

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