Navien NPE-180A -- Internal Circulation vs External Circulation?

[imanoob]

Hi everyone, I am planning to get this tankless water heater but after reading the manual, it seems there are two ways of operating the unit, either Internal Circulation or External Circulation (see image: https://imgur.com/a/6OY1gO4)

The way my home is currently piped is the Main water comes in, and then T's off. One side (right) goes to the kitchen area, and then other side (left) goes to the bathroom area. I plan to take the cold from the bathroom area and connect it to the Tankless that will be outside. As a result, I won't have a dedicated "external loop". My home is small, only ~1000 sqft or so. 1 story.

Questions:
1. Which method is preferred?
2. Can I use the internal mode without any issues, and still have quick access to hot water to my fixtures? I assumed that this tankless water heater (180A) model has the internal loop already so that you wouldn't have to have any sort of additional external circulation piping..

 

[Fitter30]

I'd try using the internal pump mode first and see if it meets your needs before spending money a external pump.

 

[Sponsor]

 

[Bannerman]

The internal mode will utilize the NPE-180A's internal pump to recirculate hot water only within the water heater. This is utilized to maintain the temperate within the 180A's internal buffer tank. Internal mode will not reduce the time needed for hot water to arrive at the home's faucets. Hot water arriving more quickly is not only convenient, but also will reduce water waste by reducing the water discharged to drain while waiting for hot water to arrive.

Because your home is not equipped with a dedicated recirculation return line, a thermostatically controlled recirculation valve may be mounted below the sink that is located furthest from the water heater. When the WH is configured for eternal recirc mode, the WH's internal pump will circulate hot water from the heater to the remote valve which will then utilize your home's cold water line as the return path back to the WH. To prevent the cold lines from becoming excessively warm, the thermostat control within the valve will stop recirculation flow once the hot water arriving becomes ~100 degrees.

There are recirculation valves available from various manufacturers including Navien, Watts, Taco and Grundfos. Navien's model is called NaviCirc. https://www.navieninc.com/accessories/navicirc

https://www.navieninc.com/media/videos#videos-12

Navien also offer a Hot Button accessory which will allow on-demand activation of the pump from the bathroom, washroom, laundry room or kitchen, when hot water use is anticipated. https://www.navieninc.com/accessories/hotbutton

 

[imanoob]

Thanks for the info. I may be able to add a recirculation return line from the farthest fixture. To summarize, is this the preferred method? May I ask what the point of the internal pump is then? What's the point of the pump if it's just to recirculate hot water within the WH only?

 

[Bannerman]

What's the point of the pump if it's just to recirculate hot water within the WH only?

As your Navien is an 'A' model (NPE-180'A'), it is equipped with a recirculation pump and buffer tank which are not included in the none 'A' models.

Without a volume of pre-heated water in storage, tankless models are prone to the 'cold water sandwich' issue. The commonly occurs when hot water is drawn in short bursts such as when repeatedly opening and closing the hot faucet when rinsing dishes directly after each has been washed by hand. A buffer tank provides a small volume of hot water to absorb the initial cold water bolus that would otherwise exit the WH before the gas burner has ignited and achieves the necessary heat output.

The internal pump will periodically circulate the water from the WH's internal buffer tank through the heat exchanger to ensure the buffer tank temperature is maintained at the set temperature when no hot water has been drawn for some time.

is this the preferred method?

A dedicated recirculation return line is the preferable method as it will not affect the cold water temperature leading to each fixture. Using a dedicated return line, a thermostatic recirculation valve will not be needed. A simple check-valve will need to be installed in the loop to prevent backward flow from the return line to fixtures.

When a dedicated return line cannot be retrofitted, a recirculation valve and utilization of the cold water piping as mentioned previously, often provides an easily doable option.