Navien NPE-240A2: Dedicated Recirc seems to make water cooler

[DCouncil]

Hello,
I recently updated my aging NR240A with a NPE240A2, and immediately it was a better experience. Water heats faster at fixtures, the fan noise is significantly less, principally in the 'post-purge' phase.
After about a week of having it installed, i decided to create a dedicated hot water recirc line to take advantage of the ComfortFlow pump(i have other construction going on that made it easy). I tied 1/2" PEX :donthurtme: into the 1/2" copper lines in a kitchen and a bathroom and brought them down to the heater. This is the little manifold i made (a check valve on each recirc branch and then one before it goes into the heater)

I am 99% sure i configured the unit properly, its on external, no external pump, intelligent mode, valve is open to EXT.

The recirc does seem to be flowing, both branches are warm to the touch at the manifold, and at the tie-in near the fixtures are. However, i immediately noticed that when i am taking a shower, or using a lot of hot water in the kitchen, i have these big swings in temp, and it doesn't seem to get as warm as it did, even if i go full hot.

Hoping you all can provide me with some more ideas for debugging, or point out possible mistakes in my design.
I am using Intelligent mode, so it will be watching my use for the next 7 days (maybe i just need to wait for it to settle?)
I do have ball valves on each recirc branch, so i can try to balance branches.
Is it a problem to have the recirc in a 1/2" PEX? could it be not sucking enough volume through that diameter? (The 3/4" in the pictures is only present for about 6 ft before it goes into 1/2" copper, which is what is run throughout the house)
Do i need to tweak temp settings on the unit?

Thanks again,
DIY Dave

 

[Bannerman]

The NPE-240A2 manual specifies the maximum equivalent length including the allowances for each fitting for a recirculation loop is 100' for 1/2" copper, or 500' for 3/4" copper piping.

https://www.engineeringtoolbox.com/equivalent-length-copper-pipe-fittings-d_1670.html

Because the ID for 1/2" PEX is less than 1/2" copper, there will be much greater flow restriction, especially considering the additional restriction caused by so many check-valves and internal PEX fittings which further reduce the ID of the piping.

When using PEX, recommend increasing the piping diameter by at least 1 size.

 

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[DCouncil]

While i don't think i am anywhere near the max distance for these recirc runs, i do believe there's probably something to the ID being an issue. Hmmm maybe i will try bumping the recirc line to 3/4" PEX and see what happens...

 

[DCouncil]

Just a followup to your assessment, Bannerman, how would the limited flow through recirc line be affecting the temp of the hot water at the fixture? Thanks for the infos!

 

[DCouncil]

The new setup, 3/4PEX for the whole recirc loop, coming out of 1/2" copper. it is definitely quieter, so my hope is that it is flowing more.

When we shower, the flow rate is 1.0GPM, and after we turn off the shower, the heater ramps up to 3.9GPM (i think it is heating recirc loop again). Im wondering if we just need to increase the flow rate at the shower to get the water hotter. Supporting this idea is the fact that when we fill the tub, it is super hot, and the flow is well over 1.0GPM coming from the tub spout.
The showers still seem cooler than when we were using internal recirc, but i think i understand that the heater is pushing out the contents of the recirc loop with the newly heated water. Does that sound correct?

 

[Fitter30]

Pull the shower head try it. The return line doesn't need three checks since the two returns have their own thats all thats needed. Need to feel each return line the one that is run into the side outlet of tee (bull) probably has less flow that the other ( run). To balance them could add a globe valve to balance the loops before the check. Valve is piped in the bottom out the top.

 

[DCouncil]

Hugely helpful, fitter. Thank you! I will pop the shower head off and give the high flow scenario a try this afternoon. and i was thinking the 3 check valves were a bit much. ill pop the extra off and keep it for when one of the others goes bad Seems like globe valves will allow more precise control than the ball valves i have currently, i will look into what it takes to get one of those to work on pex. Thanks again for the ideas.

 

[Fitter30]

Hugely helpful, fitter. Thank you! I will pop the shower head off and give the high flow scenario a try this afternoon. and i was thinking the 3 check valves were a bit much. ill pop the extra off and keep it for when one of the others goes bad Seems like globe valves will allow more precise control than the ball valves i have currently, i will look into what it takes to get one of those to work on pex. Thanks again for the ideas.

Ball and gate valves are good for on and off but not to regulate flow. After adjusting a globe valve always count tus from either open or closed and label it if someone turns the handle.

 

[DCouncil]

Thanks for the tip on globe valve. Hard to find at the big box stores, but ill see if i can order one online.

I did confirm tonight that the water is getting chilly when the flow gets becomes less than or equal to 1.0 gpm, any of the smart guys know if this threshold triggers a different pump speed or heating regimen or ? Overall I'm pleased with my recirc results after installing the 3/4 pex, though it is still on 'intelligent' learning and is not running the recirc unless water has been called for recently (i think?). we will see how it continues to go.

 

[Andrew Herman]

Following thread.

Thanks.

 

[John Gayewski]

Thanks for the tip on globe valve. Hard to find at the big box stores, but ill see if i can order one online.

I did confirm tonight that the water is getting chilly when the flow gets becomes less than or equal to 1.0 gpm, any of the smart guys know if this threshold triggers a different pump speed or heating regimen or ? Overall I'm pleased with my recirc results after installing the 3/4 pex, though it is still on 'intelligent' learning and is not running the recirc unless water has been called for recently (i think?). we will see how it continues to go.

I'll go ahead and disagree. The globe valve will not pay for itself for all of the trouble to find and change from a ball valve which does work at a balancing valve. A gate valve does not work for balancing too prone to hammer. A ball valve isn't the best option which I agree with, but it works well enough to leave it and balance the returns. Ball valves have been used for years as throttle-ers didn't make them the best overall choice, but considering it's what you have already in place and it works, I'd leave them.

But definitely balance those returns. You need to report back after you do. Cold water could be sitting in one of those mucking everything up.

 

[DCouncil]

After closing off each branch of recirc and allowing time for full cycling, i seem to have eliminated all the issues. My guess is that i had a bubble in one branch that was preventing it from circulating. I now have both branches on full open (ball valves still :shrug, and they both seem to be balanced 'well enough'. Cool water issues at the fixture eliminated.
Highly recommend 3/4 pex for recirc, and actually the Intelligent mode of the heater should have just finished its 'learning week' so, i should have hot water at taps during the hours that I am typically using water. Once i encounter issues i will report back.
Thanks for the tips fitter/bannerman/john