A.O. Smith Voltex MAX 66 Gal
#3 in 65 GallonFull review
A solid 240 V heater with leak protection included, sold at Lowe’s as the Signature 900 line.
Lowe's $2,579$2,579
The A.O. Smith Voltex MAX 66 Gal and the Navien NWP500 65 Gal are evenly matched, rated 3.8 and 3.8. The A.O. Smith Voltex MAX 66 Gal leads on hot water and cold rooms. The Navien NWP500 65 Gal wins on efficiency.
Navien NWP500 65 Gal
#4 in 65 GallonFull review
Navien’s stainless-tank hybrid, sold through plumbers, with a 10-year warranty that includes a year of labor. Its heat pump stops below 41 °F room air, so it suits a basement more than a cold garage.
Prices were last checked October 22, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the A.O. Smith Voltex MAX 66 Gal for hot water (83 gallons in the first hour vs 80 gallons in the first hour) and cold rooms (heat pump runs down to 37 °F room air vs heat pump runs down to 41 °F room air).
- Choose the Navien NWP500 65 Gal for efficiency (4.03 UEF vs 3.84 UEF).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every 65 gallon heat pump water heater; a clear win is highlighted. How we rank explains each one.
| Factor weight | A.O. Smith Voltex MAX 66 Gal | Navien NWP500 65 Gal |
|---|---|---|
| Overall rating | 3.8/5 | 3.8/5 |
| Efficiency 35% | 60 3.84 UEF | 74 4.03 UEF |
| Hot water 20% | 92 83 gallons in the first hour | 80 80 gallons in the first hour |
| Warranty 20% | 75 10-year tank, 10-year parts, 1-year labor | 75 10-year tank, 10-year parts, 1-year labor |
| Cold rooms 15% | 32 heat pump runs down to 37 °F room air | 16 heat pump runs down to 41 °F room air |
| Noise 10% | 69 45 dB(A) | 69 45 dB(A) |
Specifications
| A.O. Smith Voltex MAX 66 Gal | Navien NWP500 65 Gal | |
|---|---|---|
| Ratings (ENERGY STAR) | ||
| Size (nominal) | 66 gal | 65 gal |
| Tank volume (measured) | 68 gal | 61 gal |
| Uniform Energy Factor | 3.84 | 4.03 |
| First-hour rating | 83 gal | 80 gal |
| Draw pattern | High | High |
| Yearly energy use | 1,292 kWh | 1,245 kWh |
| Heat pump cut-off (low) | 37 °F | 41 °F |
| Sound level | 45 dB(A) | 45 dB(A) |
| ENERGY STAR ID | 3417561 | 4015937 |
| Installation | ||
| Power | 240 V | 240 V |
| Circuit | 30 A, 208/240 V | 30 A, 208/240 V |
| Backup element | 4,500 W | 5,000 W |
| Operating air range | 37 to 120 °F | 41 to 113 °F |
| Minimum room size | 450 cu ft | 640 cu ft |
| Size | 61 in tall, 23 in across | 63 in tall, 25 in across |
| Weight | 284 lb | 204 lb |
| Refrigerant | R-134a | R-134a |
| Features | ||
| Wi-Fi | Built in | Built in |
| App | A. O. Smith (iCOMM) | NaviLink |
| Demand response port (CTA-2045) | Yes | - |
| Leak detection | Yes | No |
| Modes | Hybrid, Heat Pump, Hot Water+ (3 levels), Guest, Electric, Vacation | Energy Saver, Heat Pump, High Demand, Electric, Vacation |
| Warranty and models | ||
| Warranty | 10 yr tank, 10 yr parts, 1 yr labor | 10 yr tank, 10 yr parts, 1 yr labor |
| Also sold as | American HPA10266H045DV, Lochinvar HPPA065KD, Reliance 10-66-DHPTA, State HPAX-66-DHPT | - |
| Released | 2024-03 | 2025-06 |