Recirculation is one of Navien's defining features. The NPE-A2 integrates a recirculation pump AND a 0.5-gallon buffer tank — the only major tankless brand that ships both. Combined, they eliminate cold-sandwich and reduce time-to-hot at distant fixtures.
Why recirculate?
Without recirculation, hot water has to push the cold pipe water out before arriving. In a large home, 30-90 seconds of cold water wasted per draw, plus the cold-sandwich effect on brief pauses between draws.
Option 1: NPE-A2 + dedicated return line
The premium configuration. NPE-A2 cabinet contains the pump; you wire a return line from the farthest fixture back to the unit's return port. The pump keeps the entire loop primed. Scheduling via NaviLink (timer windows) or manually via HotButton.
Option 2: NPE-A2 + crossover valve (retrofit)
For homes without a dedicated return line. A thermostatic crossover valve at the farthest fixture routes hot-line water through the cold line when loop temp drops below 95°F. Pump still does the work. Cold line gets occasionally warm; most homeowners don't notice.
Option 3: HotButton on-demand
Available on NPE-A2. Press a wireless button under the farthest fixture before turning on the hot tap. Pump runs for ~90 seconds (or until return temp confirms hot water at fixture), then stops. Maximum efficiency — pump only runs when needed.
Option 4: NPE-S2 or NPN + external pump
Standard (S2) and non-condensing (NPN) Navien tankless don't include a pump. Add an external Grundfos UP15 or Taco 006 inline on a return line. Approximately $200-400 in parts plus install.
The buffer tank advantage
What sets the NPE-A2 apart even from Rinnai Sensei RX: the 0.5-gallon internal buffer tank. The buffer stores enough hot water to smooth the first 5-10 seconds of any draw, handling brief faucet activations (washing hands) without needing the burner to fire at all. This is the cold-sandwich solver. Standby losses are negligible (~1% of operating cost).
Scheduling options
- Always-on: simplest, highest energy cost
- Timer-based: set windows (6-8 AM, 5-7 PM) via NaviLink
- HotButton on-demand: pump only on button press
- NaviLink scheduled HotButton — limited "smart" mode that learns basic usage patterns
Energy use ballpark
- Always-on: $20-45/month additional gas in typical 2,500 sq ft home
- Timer-based (2 windows): $8-18/month
- HotButton on-demand: $1-3/month when used
Combi boilers (NCB, NFC) — recirculation
Combi boilers don't include a DHW recirculation pump like NPE-A2 does. For DHW recirc on a combi, install an external pump on the return line, same as NPE-S2. The combi heating-side pump is separate and handles space heating circulation only.
Bottom line
If recirculation matters and you want the cleanest install, NPE-A2 is purpose-built — pump and buffer tank both inside. For retrofits without a return line, NPE-A2 with crossover valve still works well. For pure on-demand use, HotButton is the most efficient configuration in the entire tankless category.