Navien tankless as backup to solar DHW system.

michael_34

Hi,

Has anyone been using the Navien (NR 180) tankless as a back up to SDHW system?



How are they? Pros and Cons?

Thanks,

Michael

TonyS

I do

I have a Navien 180 directly fed from the solar tank I feed the Navien with 135 degree water and have the Navien set at 130. whenever the solar water becomes lower than 130 the navien picks up the difference. I have 2 showers with Moen balance valves in them. It works surprisingly well. I was really having some doubts when I piped it, but I didnt like the way I had seen them piped in diagrams using the 3 way valve. When the solar tank is above 135 I can feel the water is hotter at the head but not so much it bothers me. My 180 is not the A model. If I would do it again I would use the A model. The small buffer tank would probably be a benefit to stabilizing water temp and also eliminates minimum draw requirements.

hot_rod

do

you have a thermostatic mixer on the solar tank to limit the input to the Navian to 135F, Tony? Or can that model Navian take higher incoming temperatures?



I think most plumbing codes require no more than 120F to the faucets.



Thermostatics mix valves don't work well on the output of instant water heaters, unless they have a small storage tank attached.



It's a tough situation trying to maintain or flash the DHW to 140F for legionella, yet send "lawsuit safe" temperature to the faucets.



Many of the new solar controls have a legionella setting that allows, or forces with the back up element, the tank to 140F for a 1 hour period every 24hrs. I hear it is required in some countries already and spreading across Europe. Soon to be required here along with the no-lead laws I suspect.



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TonyS

Yes

I do have a thermostatic mixer on the solar tank. I had originally set the Navien to 120 but it wasn't hot enough for me. I don't know, maybe the Moentrol valves always mix some cold with the hot. I never took readings at the shower head, I just bumped up the Navien till I was comfortable and 130 is where it ended. I figured if I wanted to keep the Navien off I would set the solar at 135. I did this over a year and a half ago now and haven't touched it since. I lost the exchanger in my solar tank a few months ago and haven't repaired it yet. The Navien seamlessly takes over the entire load. So far I have really been impressed with it. 

hot_rod

I like

to hear actual use feedback, thanks.



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