If you own, install, or service Navien equipment...

[Dana]

Navien tankless water heaters, boilers, and combi-boiler with water tube heat exchangers have a generally good reputation. Now the bad news...

There appears to be high failure rates of the exhaust vent gasket at the sheet metal under the vent collar, and failures the combustion chamber seal at the heat exchanger. I'm not normally an alarmist, but this is both a safety and reliability concern. If you've ever opened up the unit to see oily film on things, it's either this type of failure, or cross contamination of the intake air and exhaust due to improper installation/location of the intake & exhaust vents being too close to one another.

The gasket and combustion chamber seal failures are likely restricted to Navien's water tube heat exchangers, but that would include most models. Their fire tube heat exchangers are very different, and unlikely to fail in the same way.

This guy on Long Island up until a few weeks ago was a big proponent of Navien equipment, but after replacing dozens of heat exchangers, and recently replacing the heat exchanger on his own NPE 240 discovered that the brand new heat exchanger right out of the box was leaking at the combustion chamber seal, and has now flipped 180 degrees.

The shorter video explaining where the problems are and how they can be diagnosed lives here:

A longer video showing a brand new warranty replacement heat exchanger that failed right out of the box lives here:

<It's a bit tedious- scroll forward to the 49 minute mark as he's filling & purging the unit after replacing it, followed by the initial firing and testing for leaks with soapy water.

These are some of the most popular tankless gas water heaters and combi heaters in my area. YMMV.

 

[Arseniy M]

Yes, unfortunately these units with that type of heat exchanger seem to be failing left-and-right. I met this guy Mike from the videos a little over 2 years ago when he was over at my house recommending none other than NCB-240e. Back then I was just another underinformed home owner but fortunately before I agreed to anything Long Island and other parts of NY were hit by that moratorium on new gas hookups. That's when I started reading up on things -- including articles by Dana and after doing the "napkin math" I realized that NCB-240e is WAY oversized for the actual heat loss of my house and also with 5 people in the house including a teenage girl and a couple of 4 year-olds -- all the laundry, dishwashing and showers -- pretty much mean that any combi is NOT a good fit for my current situation (thanks, again Dana!). Believe it or not I was considering an NHB-080 plus indirect, but that boiler has the exact same type of heat exchanger, so no to that. On top of that HTP is discontinuing their entire UFT line, 80 is already almost impossible to get. Not sure what I'm going to do.

 

[Sponsor]

 

[Dana]

Believe it or not I was considering an NHB-080 plus indirect, but that boiler has the exact same type of heat exchanger, so no to that. On top of that HTP is discontinuing their entire UFT line, 80 is already almost impossible to get. Not sure what I'm going to do.

A fire-tube Lochinvar Noble, perhaps? The WHB/KHB085N throttles all the way down to 8500 BTU/hr (input), the WHB/KHB055N drops down to 8300 BTU/hr (not a big difference.) The NKB080N also runs as low as 8300 BTU/hr.

I'm hopeful that the UFT's aren't really going away for good- they seem like really nice units for the money. If Kiturami (the Korean manufacturer) replaces that product line with something even nicer and HTP takes them on it wouldn't hurt my feelings though.

 

[Arseniy M]

Yes! All great minds think alike. NKB080N is one of the boilers that I'm considering. Very nice boiler, albeit significantly more expensive than NHB-080 or UFT-80. Also, Lochinvar is pretty adamant about piping it primary/secondary. Right now half of me wants to go that route, but the other half wants something simpler like a Weil-McLain CGa-3 (maybe even CGa-25 -- actual heat loss of my house at our design temp of about 15*F is just under 30kbtu/h). Someone on another forum suggested to look into reverse indirect such as Turbomax 23. The smallest one has an internal volume of 26 gallons I believe. Should work just fine with CGa-3, but not quite sure how to get return water under 130*F to get condensing efficiency out of the Lochinvar for most of the heating season. I do have enough radiation in the house for that. What is also interesting is -- the tank could be set up in such a way that in heating mode it acts as a buffer -- essentially storing BTUs. Very little standby loss -- comparable to the standard indirect. Can't seem to figure out the math though In order to get "limitless" hot water out of it, say at 120*F via a mixing valve, my understanding is that the tank needs to be stored at a much higher temperature, but how to "cool" it for heating when one of the thermostats start calling?

 

[Dana]

Yes! All great minds think alike. NKB080N is one of the boilers that I'm considering. Very nice boiler, albeit significantly more expensive than NHB-080 or UFT-80. Also, Lochinvar is pretty adamant about piping it primary/secondary. Right now half of me wants to go that route, but the other half wants something simpler like a Weil-McLain CGa-3 (maybe even CGa-25 -- actual heat loss of my house at our design temp of about 15*F is just under 30kbtu/h). Someone on another forum suggested to look into reverse indirect such as Turbomax 23. The smallest one has an internal volume of 26 gallons I believe. Should work just fine with CGa-3, but not quite sure how to get return water under 130*F to get condensing efficiency out of the Lochinvar for most of the heating season. I do have enough radiation in the house for that. What is also interesting is -- the tank could be set up in such a way that in heating mode it acts as a buffer -- essentially storing BTUs. Very little standby loss -- comparable to the standard indirect. Can't seem to figure out the math though In order to get "limitless" hot water out of it, say at 120*F via a mixing valve, my understanding is that the tank needs to be stored at a much higher temperature, but how to "cool" it for heating when one of the thermostats start calling?

There is a lot to unpack when using a reverse indirect as a heating system buffer- be sure to do all of the math before settling on something as small as the Turbomax 23. My own home's heating system is centered around an Ergomax E44 (48 gallons), but with a modulating burner that maxes out at ~60,000 BTU/hr (as-used in this system), maintained between 122F (lo-limit) and 130F (high limit).

It's not perfect, but it's not terrible either, but domestic hot water service would suffer were it not for the ~50% return efficiency drainwater heat recovery heat exchanger sufficient to deliver the "endless shower" experience. As it it just barely fills a standard tub- I'd need to crank the storage temp well above the condensing zone or install a much bigger burner to fill bigger tubs. And that's with twice the storage volume of a Turbomax 23.