So our new hot water heater (Navien NPE-240A2) has a dedicated recirc line and pump to make sure you have hot water instantly on the other side of the house, but the built-in logic is incredibly inefficient, which runs every 30 minutes 24/7, wasting a ton of gas/energy in the process, and emitting GHGs. There is an "intelligent" mode that attempts to learn your schedule, but it was wildly off in our first couple weeks of use.
One way Navien tries to make this more efficient is by having folks install a "Hot Button", which is a physically wired button in the rooms where you want to start the recirc pump manually. While this would add a lot more efficiency, pressing buttons != automation, but at least I thought I could use a relay to simulate this button press within Home Assistant logic!
Thankully, these newer units come with the Hot Button PCB pre-installed, so you don't have to buy any new hardware for the water heater. I purchased a simple Zigbee Dry Relay and wired it up to the Navien's hot button PCB.
After getting that working, had some fun playing around with some events/automations that would ensure it ran the least amount of time while ensuring instant hot water when we need it most.
When my wife and I get out of bed first thing in the morning on weekdays (to have the shower ready to go).
When our son is getting ready for bed so he has instant hot water for brushing his teeth.
When motion is sensed in the kitchen and if the recirc pump hasn't ran in the last 30 minutes (during certain times of day).
Whenever our shower light turns on, in case we're taking more than one shower a day for some reason.
Immediately after we come home from being away for awhile, since we're likely to need instant hot water for various reasons.
Now that this is all working, the recirc pump is running at a 90% decrease in terms of overall run time and we don't notice any change in comfort!
Pics of the install/configuration
NPE-Advanced
The most advanced condensing tankless water heaters in the industry with exclusive ComfortFlow® technology for continuous hot water.
- Exclusive ComfortFlow® internal recirculation pump and buffer tank.
- Earn up to 3 LEED points with recirculation.
- Lower the HERS home index score.
- Wi-Fi enabled with NaviLink® add-on.
- Optional HotButton™ on demand control kit.
- 2013 AHR Innovation Award Winner.
Exclusive built-in recirculation system included on all NPE-A models
Navien ComfortFlow® is the first and only system that incorporates a built-in insulated buffer tank and recirculation pump. The buffer tank eliminates the “cold water sandwich” effect and issues of minimum flow rates commonly found in other tankless water heaters. The recirculation pump saves on water bills by reducing the time to get hot water. When activated, the optional ComfortFlow mode results in additional energy usage.
Optional Wi-Fi remote control system
NaviLink makes it easy to communicate with your Navien systems anywhere internet service is accessible. The NaviLink module attaches easily to any new or existing* Navien tankless water heater, combi‐boiler and
boiler.
* Existing installations may require the purchase of a new main PCB and front control panel. Units produced on or after 2-22-16 will be compatible out of the box.
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