Product Review of the Navien Tankless Water heater Models NR-180A, NR-210A, & NR-240A.

Tankless water heaters are not really my thing. I never run out of hot water with my storage heater, I frequently use very low flows of hot water which is virtually impossible for tankless water heaters to provide.  Tankless hot water heaters require .5 to .75 gpm of hot water flow to turn on.  Drop below that and the heater turns off again. That makes it hard or impossible to get a small steady stream of warm water from the faucet.

Navien seems to have addressed these problems with its "A" models. The “A” models have a unique feature, at least one I have not run across before, a built in buffer tank and circulating pump.  According to the Navien literature you will be able to utilize flows as low as .1 to .2 gallons per minute without the heater shutting off. 

This new feature should also eliminates the fabled “cold water sandwich” which tankless water heaters are known for.  The Navien tankless heaters circulate the water internally between the heat exchanger and a small buffer tank.  With the A models can  connect them to a dedicated return line and the internal pump will circulate the hot water like a standard hot water circulating system.

Hot Water Recirculation with Tankless Heaters

I’m not advocating hot water circulating systems, I prefer demand systems, but I’m sure there are some people out there that would find it useful to have a hot water circulating system some type in combination with their tankless water heater.  It’s the low flow capability of these heaters that I think is a really great thing.  It will result in water saved.

From the Navien website it sounds like the heater is well constructed. It has stainless steel heat exchangers and boasts a 98% efficiency, the highest in the industry.  The exhaust temperature is low enough to use PVC for the venting. 

Here are the specifications for the three models with the built in buffer tank and circulating pump.
 

Navien Model NR-240A

Input 17,000~199,000 BTU/h

Thermal Efficiency 98%

Energy Factor 0.95

Flow Rate At 35˚F Rise : 11 GPM

At 45˚F Rise : 8.6 GPM

At 77˚F Rise : 5.1 GPM 

Navien Model NR-210A

Input 17,000~180,000 BTU/h

Thermal Efficiency 98%

Energy Factor 0.94

Flow Rate At 35˚F Rise : 10.0 GPM

At 45˚F Rise : 7.7 GPM

At 77˚F Rise : 4.6 GPM 
 

Navien Model NR-180A

Input 15,000~150,000 BTU/h

Thermal Efficiency 98%

Energy Factor 0.94

Flow Rate At 35˚F Rise : 8.3 GPM

At 45˚F Rise : 6.5 GPM

At 77˚F Rise : 3.8 GPM 

Navien claims their condensing technology  uses less gas than standard water heaters and that it results in less CO2 Emissions than other brands of tankless hot water heaters.

The Eco Pre-mixed Burner dramatically reduces NOx emission levels, making it the lowest emission levels in the industry.  Interestingly Navien states that it’s Condensing 98% tankless water heater has become more eco-friendly by dissolving NOx in condensed water to neutralize the alkaline sewage in your house, improving water quality.  Sounds good, but I wonder if it is significant in any way?

I’m not saying that the Navien models are the best tankless water heaters, I don’t know how they hold up over time or much of anything else about them.  But I do think they have at least in my opinion the best idea for a tankless water heater, being able to deliver low flows of water without shutting off.

The Navien models will work great with demand systems and with it’s low required turn on flow it will probably work with just about any of the hot water recirculating systems and demand type systems on the market.