Navien NPE-240A2 x2 units--please help me configure

[Jughead135]

New to the forum (great site!), and I'm nobody's plumber. Trying to figure out how best to use the WHs in my new home. Pics attached.

Existing DHW install in new home: 2x Navien NPE-240A2 units, side by side, wall mounted. Water supplied by well. Single cold water supply line, "T"-valve supplies both heaters. Another "T"-valve combines the output of each to a single hot water line. Separate intake & exhaust venting for each. NO recirculation return line installed (new construction--**slaps forehead**). NO communication line installed between them. Shortly after the "T"-valve, the hot (and cold) water supply lines split and supply two distinct areas of the house (with further splits visible before the lines disappear into the walls, but not enough to account for every output, so obviously more splitting downstream).

Q1) Are these two "working together" in any sense? Will I improve the operation with the addition of the Ready-Link Cascade Cable? That appears to be simple plug-in wiring & menu configuration--no plumbing, correct?

Q2) I note that the cold water supply line entering one or both WHs gets hot, a consequence (I assume) of how they're plumbed. Is this a problem? I suspect it's due to using RECIRC mode (in internal). Am I missing some check valves (perhaps one each on the cold water supply lines to each unit)? Does that apply to the A2 units w/ return via the main supply line & not the recirc connector? [As seen in the pics, I currently have recirc turned off & one unit completely powered down / water off for troubleshooting. This issue has NOT recurred in this configuration.]

Q3) Despite enabling the internal recirculation, it takes a long time to get hot water. I assume the NaviCirc bypass valve is the way to go in my situation (no recirc return line plumbed in the house)? I'm finding conflicting/confusing information on how those are installed:

Q4) NaviCirc: Is there plumbing required at the heater(s) to connect from the cold water supply line (to be used as a return) to the recirculation inlet fitting? [I gather that's NOT required for my A2 units, but IS required for the A--a point of considerable confusion!] If so, should that be to one or both units? If not, will I need some sort of check valve in the supply line so the recirculating water goes into the heater and no chance of backflowing the well; or does the action of the reirc pump take care of that?

Q4) NaviCirc: Given the two major "zones" of the house being fed by both the cold & hot water supplies, would I then want to install TWO (or more) bypass valves, one at the distant end of each zone? Or perhaps at the "most important" point, not necessarily farthest? [Thinking master bedroom & kitchen.] Will such a setup require fancier plumbing, or will it "just work"? I've seen this question asked & answered elsewhere on the forum--would doing do necessitate additional check valves at each point of installation? Should recirculation be enabled on both units, or only one?

Q5) Large house, generally only occupied by two of us--but frequently full-up on visitors. Considering Q1 above (Ready-Link Cascade Cable), would I be better off getting them "talking" to each other, or simply manually running a single unit, turning the other one on & off as required for larger groups? Or maybe both will be needed in winter? (We've never exceeded the capacity during our short time here--but, both units were running during the cold months.) Will the cable "shut down" one unit? How does mixing heated water with cold (from the non-operative heater) achieve fully-heated water?

Q6) Just how hot ("warm"; "tepid"; pick your adjective) is my *cold* water going to get, and how long to get cold? I'm particularly sensitive in the kitchen, where we have drinking water & two ice makers (freezer & a stand-alone)--feeding heated water to those taps just doesn't seem like a good idea....



Please note: I'm looking at the "Quick Installation Guide," Step 6 on p. 2., found at https://www.navieninc.com/downloads/npe-2-quick-installation-guide-en. I believe the diagrams may be mis-matched?? The detailed diagram under "...using the Cold Water Inlet" appears to describe the "...using the Recirculation Inlet," and vice-versa; whereas the simplified diagrams under each heading appear to be correct (and not match the detailed ones). This is a large part of my confusion, so please set me straight....

Love the system, but I'm pretty sure I'm not getting all I can out of it at the moment. Happy to provide more pics if needed. Thanks for any help or pointers you can provide!

 

[Jughead135]

Q2) I note that the cold water supply line entering one or both WHs gets hot, a consequence (I assume) of how they're plumbed. Is this a problem? I suspect it's due to using RECIRC mode (in internal). Am I missing some check valves (perhaps one each on the cold water supply lines to each unit)? Does that apply to the A2 units w/ return via the main supply line & not the recirc connector? [As seen in the pics, I currently have recirc turned off & one unit completely powered down / water off for troubleshooting. This issue has NOT recurred in this configuration.]

I finished cycling through different configurations--I'm confident this issue is due to the recirculation.

- With one unit OFF / water turned off to that unit & the other ON, there was no heating of either cold water supply, with internal recirculation ON or OFF
- With both units ON / water on, recirculation OFF: no heating
- Both units ON / recirculation ON a single unit: the cold water supply lines heat up (rather rapidly upon the recirc cycle starting). Both sides heat up, but it seems to happen faster/hotter on the opposite unit
- Both units ON / recirculation ON both: This was how things were set before; both sides heat up.

I've currently got the units set to one ON, one OFF (both at the panel and the water supply), with the internal recirc ON for the operating one. Plenty of hot water with only two of us at the house for the moment, and no heating issues as noted in the first bullet above.

So, the question remains: Is this a problem?

And: Do I need check valves (or other controls) in-line somewhere? If the recirc pump can force water down the cold water supply line, is it also forcing it to backflow to the well supply?

 

[Sponsor]

 

[Bannerman]

Because the hot water outlets are joined together, both WHs function together as a Cascade system, with each WH supplying 50% of hot water flow to each household fixture. Each WH must be configured for Cascade operation, and the cascade communication cable will.be required, allowing one unit to function as the Main (master), and the 2nd unit to function as a Sub (slave), controlled by the main unit

As 2 GPM recirculation flow is recommended for each unit, a recirculation return may either be plumbed to both units, with each set to external circulation, or recirculation return may be plumbed to only the Main unit, so the Main will require external circulation to be programmed, and the Sub unit will require internal circulation to be programmed.

Internal circulation will not speed up hot water delivery to distant fixtures, but will permit each A2 unit's internal buffer tank temperature to be maintained at the desire water temperature, during periods when no hot water is utilized. Tankless units normally have 0 hot water in storage to supply immediate hot water needs. As the gas burner will not fire until there is water flow through the unit, the water initially exiting the WH will be cold until the burner is activated and achieves full output. When short bursts of hot water are utilized, such as while rinsing dishes, there will often occur a hot water 'sandwich' condition whereby hot water in the pipes will be followed by brief bursts of cold water, each time a hot faucet is activated. The small internal buffer tank within each of your A2 units, allows the initial cold water exiting the heat exchanger, to mix with the constant hot water within the buffer tank, thereby increasing the temperature of the initial flow from each WH, thereby reducing/eliminating the cold water sandwich condition and allowing the initial hot water flow to be hotter than it would be otherwise.

A dedicated recirculation return line will always be superior compared to using a cross over valve such as a NaviCirc. A NaviCirc is a hybrid option when installing a dedicated return line is not possible or practical. To prevent cold water lines from filling with extremely hot water, a NaviCirc or similar valve will stop hot water recirculation flow once the hot water arriving at the device has reached a specific temperature. IIRC, NaviCirc will stop circulation flow once 100°F hot water is sensed at the device, whereas no temperature limiting device will be utilized when a dedicated recirculation return line is utilized.

Here is a link to the NPE-A2 Installation and Operation Manual. Cascade system configuration, including for recirculation, commences on page 70.

https://www.navieninc.ca/downloads/npe-2-installation-and-operation-manual-en

 

[Fitter30]

Ask the plumbing company to have the local rep of navian to meet with your plumber at the house. They are plumbers that haven't been trained on the correct installation of two units.

 

[Jughead135]

Thanks, @Bannerman ! I'm new here, but I've read enough to know you're the expert on this stuff, I appreciate you chiming in.

Because the hot water outlets are joined together, both WHs function together as a Cascade system, with each WH supplying 50% of hot water flow to each household fixture. Each WH must be configured for Cascade operation, and the cascade communication cable will.be required, allowing one unit to function as the Main (master), and the 2nd unit to function as a Sub (slave), controlled by the main unit

So, in my current configuration (i.e., no comm cable, and before I shut one down), am I "cascading" at all? Or are both of them trying to do their thing independently (which is what I assume has to be the case)?

Priority one is getting hot water (of course)--which, one unit is doing just fine, at least when there's just the two of us here. We'll see what happens with a house full of guests.

After that, the long-term health of the units is next in line. Following that is economy (gas + electric). So: It seems obvious that when I *do* use both units (say, with a bunch of visitors), I'll want the cascade cable & properly set up master/slave units. Otherwise: am I better off shutting one down completely and letting one handle the relatively light load? Or should I "set it & forget it," and trust the software to operate both units at an ideal level for longevity & economy?

The builder clearly felt two units were called for based on the size of the house (5 bd / 5 1/2 ba)--but it doesn't seem like it's optimally set up. (I think it's criminal that he didn't install return lines for a recirculation system, but that's a different thread.)

As 2 GPM recirculation flow is recommended for each unit, a recirculation return may either be plumbed to both units, with each set to external circulation, or recirculation return may be plumbed to only the Main unit, so the Main will require external circulation to be programmed, and the Sub unit will require internal circulation to be programmed.

Would it be the same answer if using a crossover valve (NaviCirc or otherwise)? I don't see how it could be practical to add a return line at this point.... Is one of those options (use Main to recirculate or both) "better" than the other? Does the cascade configuration optimize this function?

What if I install two crossover valves (one on each main sub-system)? (Or is that a bad idea altogether? Understood Navien says "just one"--but I also read multiple people have done it, and I can't fathom how a crossover on one end of the house will help me on the other end, when the lines split about two feet from the WHs...)

And: With my A2 units, my understanding is that using a crossover means I do NOT need or want to plumb anything to the return input--correct?

Internal circulation will not speed up hot water delivery to distant fixtures, but will permit each A2 unit's internal buffer tank temperature to be maintained at the desire water temperature, during periods when no hot water is utilized. Tankless units normally have 0 hot water in storage to supply immediate hot water needs. As the gas burner will not fire until there is water flow through the unit, the water initially exiting the WH will be cold until the burner is activated and achieves full output. When short bursts of hot water are utilized, such as while rinsing dishes, there will often occur a hot water 'sandwich' condition whereby hot water in the pipes will be followed by brief bursts of cold water, each time a hot faucet is activated. The small internal buffer tank within each of your A2 units, allows the initial cold water exiting the heat exchanger, to mix with the constant hot water within the buffer tank, thereby increasing the temperature of the initial flow from each WH, thereby reducing/eliminating the cold water sandwich condition and allowing the initial hot water flow to be hotter than it would be otherwise.

Thank you. I'd understood the bit about internal not speeding up delivery, but your explanation has finally let me grasp what the "cold water sandwich" effect is that I've been reading.

A dedicated recirculation return line will always be superior compared to using a cross over valve such as a NaviCirc. A NaviCirc is a hybrid option when installing a dedicated return line is not possible or practical. To prevent cold water lines from filling with extremely hot water, a NaviCirc or similar valve will stop hot water recirculation flow once the hot water arriving at the device has reached a specific temperature. IIRC, NaviCirc will stop circulation flow once 100°F hot water is sensed at the device, whereas no temperature limiting device will be utilized when a dedicated recirculation return line is utilized.

Here is a link to the NPE-A2 Installation and Operation Manual. Cascade system configuration, including for recirculation, commences on page 70.

https://www.navieninc.ca/downloads/npe-2-installation-and-operation-manual-en

I think I've read 95°F for the NaviCirc, but, understood on the concept.

My kitchen is both the farthest point (of one of the two main splits), and tied for most desirable for fast hot water with the master bedroom (on the other main split). However, I don't love the idea of feeding 95° water to the stand-alone ice maker, the freezer ice maker, or the drinking water faucet. Is this really the choice I have to make?


Any thoughts on the cold water supply lines getting hot when the internal recirc is running & both units are active?


Thanks again for your help!! As frustrating as this is, I'm actually enjoying learning how my new home's systems work...!

 

[Breplum]

The gas supply lines should be full 3/4" not choked down as you have, and read the rating on the flex to match btu.
Does not look like you followed the NavCirc instructions relative to check valves. You need two, one on each cold inlet.

https://www.navieninc.com/downloads/navicirc-installation-and-operation-manual-en.

Your bumbling plumber should read instructions and at worst, call Navien and live stream this embarrassing installation to the tech desk.
Navien Technical Support offers real time remote video support assistance through Visual Support - RemoteCall on your Apple or Android smartphone. This video support assistance allows you to share live job site video with our technicians using your smartphone camera.
They will not talk to homeowners, only plumbers who have knowledge and test equipment, though, you have to install correctly to start
- without question you need the ready-link cable and needs configuration
-not drip legs on gas !!!
-not piped for two units as per Navien drawings/engineers

 

[GReynolds929]

How big is the room they are located in? I find it unlikely that there is enough makeup air for both. Ideally they should be getting air from outside anyway.

 

[Jughead135]

Ask the plumbing company to have the local rep of navian to meet with your plumber at the house. They are plumbers that haven't been trained on the correct installation of two units.

That's something I'd been thinking of doing--not sure if Navien has any local reps, we're somewhat rural.... Thanks for the pointer!

 

[Jughead135]

The gas supply lines should be full 3/4" not choked down as you have, and read the rating on the flex to match btu.
Does not look like you followed the NavCirc instructions relative to check valves. You need two, one on each cold inlet.

https://www.navieninc.com/downloads/navicirc-installation-and-operation-manual-en.

Your bumbling plumber should read instructions and at worst, call Navien and live stream this embarrassing installation to the tech desk.
Navien Technical Support offers real time remote video support assistance through Visual Support - RemoteCall on your Apple or Android smartphone. This video support assistance allows you to share live job site video with our technicians using your smartphone camera.
They will not talk to homeowners, only plumbers who have knowledge and test equipment, though, you have to install correctly to start
- without question you need the ready-link cable and needs configuration
-not drip legs on gas !!!
-not piped for two units as per Navien drawings/engineers

Wow--OK, sounds like you're saying I've got much bigger issues than attempting to optimize things. I will definitely follow up with Navien--thank you!

FTR, there's no NaviCirc (or any recirculation) installed as yet. Chasing down this option is what's gotten me to where I am now.... Does that fact alter you answer about needing check valves, and/or my question about what's causing the intakes to heat up (and do I need to care)...?

 

[Jughead135]

How big is the room they are located in? I find it unlikely that there is enough makeup air for both. Ideally they should be getting air from outside anyway.

Approx 22' x 14'. Doorway is a "barn door" sliding style--so, not truly "vented," but not sealed in any sense.

I never expected this question, either. Man, I've got some work to do....

 

[Breplum]

No check valve needed if no NavCirc.
Definitely need link cable and setting up for twin units.

 

[Jughead135]

Ask the plumbing company to have the local rep of navian to meet with your plumber at the house. They are plumbers that haven't been trained on the correct installation of two units.

That's something I'd been thinking of doing--not sure if Navien has any local reps, we're somewhat rural.... Thanks for the pointer!

So, it turns out that Navien apparently does not have any local reps. I really think this was a great approach, but it's not available to me. Any other suggestions on how to get Navien involved?

My builder's guys are coming over today for some unrelated punch-list stuff. I'll discuss the WH issues with them, so at least that discussion will be started....

 

[Fitter30]

Plumber could contact navian talk to them how to set the units up, take pictures if they need them and how the units are wired between them.