Both are heat pump water heaters. The NWP500S065AUMB is more efficient (UEF 4.03 vs 3.70). The HPTS-66-2 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-66-2 A. O. Smith · Heat Pump | NWP500S065AUMB Navien · Heat Pump |
|---|---|---|
| UEF | 3.70 | 4.03Difference: 0.33 |
| Capacity | 67 galDifference: 6 gal | 61 gal |
| First Hour Rating | 82 galDifference: 2 gal | 80 gal |
| kW Input | 4.50 kWDifference: 0.50 kW | 5 kW |
The NWP500S065AUMB leads on efficiency. But does it fit? Sizing guide
Physical dimensions
| Dimension | HPTS-66-2 | NWP500S065AUMB |
|---|---|---|
| Height | 61.50"Difference: 1.50" | 63" |
| Width | 26.50" | 25"Difference: 1.50" |
| Depth | 26.50" | 25"Difference: 1.50" |
| Weight | — | 204 lbs |
Fit checked. Now the operating cost.
Operating cost
| Cost | HPTS-66-2 | NWP500S065AUMB |
|---|---|---|
| Annual Operating Cost | $213/yrDifference: $2/yr | $215/yr |
| 10-Year Operating Cost | $2,130Difference: $20 | $2,150 |
| Annual Energy | 1,233 kWhDifference: 12 kWh | 1,245 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-66-2 ranges from $136/yr (ND) to $513/yr (HI). The NWP500S065AUMB ranges from $137/yr (ND) to $518/yr (HI).
$2/yr separates them. Install requirements determine the upfront gap. Installation accessories
Installation requirements
| Requirement | HPTS-66-2 | NWP500S065AUMB |
|---|---|---|
| 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-66-2 | NWP500S065AUMB |
|---|---|---|
| Tank | 10 yridentical | |
| Parts | — | 10 yr |
| Labor | — | 1 yr |
Features
| Feature | HPTS-66-2 | NWP500S065AUMB |
|---|---|---|
| Wi-Fi / Smart | Yesidentical | |
| Noise Level | 45 dBidentical | |
| Refrigerant | R-134aidentical | |
Decision split
Pick this one if...
Navien NWP500S065AUMB
- Peak efficiency is the priority (UEF 4.03)
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