Both are heat pump water heaters. The NWP500S050AUMB is more efficient (UEF 3.85 vs 3.75). The NWP500S050AUMB saves $1/year to operate. All figures from published specs and EIA energy prices.
Performance
| Spec | NWP500S050AUMB Navien · Heat Pump | REHP50BM Rinnai · Heat Pump |
|---|---|---|
| UEF | 3.85Difference: 0.10 | 3.75 |
| Capacity | 44 gal | 46 galDifference: 2 gal |
| First Hour Rating | 65 gal | 73 galDifference: 8 gal |
| kW Input | 5 kW | 4.90 kWDifference: 0.10 kW |
The NWP500S050AUMB leads on efficiency. But does it fit? Sizing guide
Physical dimensions
| Dimension | NWP500S050AUMB | REHP50BM |
|---|---|---|
| Height | 63"Difference: 3.40" | 66.40" |
| Width | 21.70"identical | |
| Depth | 21.70"Difference: 0.30" | 22" |
| Weight | 181 lbsDifference: 31 lbs | 212 lbs |
The REHP50BM is taller. Fit checked. Now the operating cost.
Operating cost
| Cost | NWP500S050AUMB | REHP50BM |
|---|---|---|
| Annual Operating Cost | $145/yrDifference: $1/yr | $146/yr |
| 10-Year Operating Cost | $1,450Difference: $10 | $1,460 |
| Annual Energy | 840 kWhDifference: 4 kWh | 844 kWh |
10-year modeled difference is $10. At this scale, local energy rates, usage patterns, and install costs matter more than the efficiency delta.
Costs vary by state. The NWP500S050AUMB ranges from $93/yr (ND) to $350/yr (HI). The REHP50BM ranges from $93/yr (ND) to $351/yr (HI).
$1/yr separates them. Install requirements determine the upfront gap. Installation accessories
Installation requirements
| Requirement | NWP500S050AUMB | REHP50BM |
|---|---|---|
| Voltage | 240Videntical | |
| Amperage | 23ADifference: 1A | 24A |
| Breaker | 30Aidentical | |
| Condensate Drain | Yesidentical | |
Same electrical requirements. Swapping between these units should not require electrical changes.
Warranty
| Coverage | NWP500S050AUMB | REHP50BM |
|---|---|---|
| Tank | 10 yridentical | |
| Parts | 10 yridentical | |
| Labor | 1 yridentical | |
Features
| Feature | NWP500S050AUMB | REHP50BM |
|---|---|---|
| Wi-Fi / Smart | Yesidentical | |
| Noise Level | 45 dB | — |
| Refrigerant | R-134aidentical | |
Decision split
Pick this one if...
Navien NWP500S050AUMB
- Your ceiling or space is under 66.40"
- Peak efficiency is the priority (UEF 3.85)
Pick this one if...
Rinnai REHP50BM
- You have high peak demand (73 gal FHR)
Neither if...
- You have no floor drain and cannot add condensate handling
- Your home only has 120V service and you cannot upgrade the panel
- Your install space is under 700 sq ft of open air
Common accessories for this type of installation.
Common install considerations for heat pump units
What is required depends on your existing installation, local code, and installer preference.
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Related
Sources. ENERGY STAR, manufacturer spec sheets, EIA average energy prices.Methodology