Both are heat pump water heaters. Efficiency is nearly identical. The REHP80BM saves $7/year to operate. All figures from published specs and EIA energy prices.
Performance
| Spec | NWP500S080AUMB Navien · Heat Pump | REHP80BM Rinnai · Heat Pump |
|---|---|---|
| UEF | 4.05Difference: 0.05 | 4 |
| Capacity | 74 gal | 75 galDifference: 1 gal |
| First Hour Rating | 85 gal | 91 galDifference: 6 gal |
| kW Input | 5 kW | 4.90 kWDifference: 0.10 kW |
But does it fit? Sizing guide
Physical dimensions
| Dimension | NWP500S080AUMB | REHP80BM |
|---|---|---|
| Height | 71.60"Difference: 2.60" | 74.20" |
| Width | 25"Difference: 0.60" | 25.60" |
| Depth | 25"Difference: 0.69" | 25.69" |
| Weight | 220 lbsDifference: 50 lbs | 270 lbs |
The REHP80BM is taller. Fit checked. Now the operating cost.
Operating cost
| Cost | NWP500S080AUMB | REHP80BM |
|---|---|---|
| Annual Operating Cost | $218/yr | $211/yrDifference: $7/yr |
| 10-Year Operating Cost | $2,180 | $2,110Difference: $70 |
| Annual Energy | 1,265 kWh | 1,225 kWhDifference: 40 kWh |
10-year modeled difference is $70. At this scale, local energy rates, usage patterns, and install costs matter more than the efficiency delta.
Costs vary by state. The NWP500S080AUMB ranges from $139/yr (ND) to $526/yr (HI). The REHP80BM ranges from $135/yr (ND) to $510/yr (HI).
$7/yr separates them. Install requirements determine the upfront gap. Installation accessories
Installation requirements
| Requirement | NWP500S080AUMB | REHP80BM |
|---|---|---|
| Voltage | 240Videntical | |
| Amperage | 23ADifference: 1A | 24A |
| Breaker | 30Aidentical | |
| Condensate Drain | Yes | — |
Same electrical requirements. Swapping between these units should not require electrical changes.
Warranty
| Coverage | NWP500S080AUMB | REHP80BM |
|---|---|---|
| Tank | 10 yridentical | |
| Parts | 10 yridentical | |
| Labor | 1 yridentical | |
Features
| Feature | NWP500S080AUMB | REHP80BM |
|---|---|---|
| Wi-Fi / Smart | Yesidentical | |
| Noise Level | 45 dB | — |
| Refrigerant | R-134aidentical | |
Decision split
Pick this one if...
Navien NWP500S080AUMB
- Your ceiling or space is under 74.20"
Pick this one if...
Rinnai REHP80BM
- You have high peak demand (91 gal FHR)
Neither if...
- 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