Both are heat pump water heaters. The NWP500S050AUMB is more efficient (UEF 3.85 vs 3.80). The HPTS-50-2 saves $2/year to operate. All figures from published specs and EIA energy prices. UEF measures lab efficiency under DOE test conditions. Annual cost uses that rating plus national average energy prices. Different draw patterns, local rates, and standby losses can cause the rankings to diverge.
Performance
| Spec | HPTS-50-2 A. O. Smith · Heat Pump | NWP500S050AUMB Navien · Heat Pump |
|---|---|---|
| UEF | 3.80 | 3.85Difference: 0.05 |
| Capacity | 46 galDifference: 2 gal | 44 gal |
| First Hour Rating | 65 galidentical | |
| kW Input | 4.50 kWDifference: 0.50 kW | 5 kW |
The NWP500S050AUMB leads on efficiency. But does it fit? Sizing guide
Physical dimensions
| Dimension | HPTS-50-2 | NWP500S050AUMB |
|---|---|---|
| Height | 63"identical | |
| Width | 22" | 21.70"Difference: 0.30" |
| Depth | 22" | 21.70"Difference: 0.30" |
| Weight | — | 181 lbs |
Fit checked. Now the operating cost.
Operating cost
| Cost | HPTS-50-2 | NWP500S050AUMB |
|---|---|---|
| Annual Operating Cost | $143/yrDifference: $2/yr | $145/yr |
| 10-Year Operating Cost | $1,430Difference: $20 | $1,450 |
| Annual Energy | 831 kWhDifference: 9 kWh | 840 kWh |
10-year modeled difference is $20. At this scale, local energy rates, usage patterns, and install costs matter more than the efficiency delta.
Costs vary by state. The HPTS-50-2 ranges from $92/yr (ND) to $346/yr (HI). The NWP500S050AUMB ranges from $93/yr (ND) to $350/yr (HI).
$2/yr separates them. Install requirements determine the upfront gap. Installation accessories
Installation requirements
| Requirement | HPTS-50-2 | NWP500S050AUMB |
|---|---|---|
| Voltage | 240Videntical | |
| Amperage | 22ADifference: 1A | 23A |
| Breaker | 30Aidentical | |
| Condensate Drain | Yesidentical | |
Same electrical requirements. Swapping between these units should not require electrical changes.
Warranty
| Coverage | HPTS-50-2 | NWP500S050AUMB |
|---|---|---|
| Tank | 10 yridentical | |
| Parts | — | 10 yr |
| Labor | — | 1 yr |
Features
| Feature | HPTS-50-2 | NWP500S050AUMB |
|---|---|---|
| Wi-Fi / Smart | Yesidentical | |
| Noise Level | 45 dBidentical | |
| Refrigerant | R-134aidentical | |
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