Ariston NUOS Side-Connect 40 Gal
#15 in 40–50 GallonFull review
A non-Midea design with a leak sensor built in and a 10-year tank and parts warranty, sold through plumbing dealers. It is louder than most here.
The Ariston NUOS Side-Connect 40 Gal is the better heat pump water heater overall, rated 3.3 to 3.1. The Ariston NUOS Side-Connect 40 Gal leads on hot water and cold rooms. The A.O. Smith Voltex MAX 40 Gal wins on noise.
A.O. Smith Voltex MAX 40 Gal
#17 in 40–50 GallonFull review
A solid 240 V heater with leak protection included, sold at Lowe’s as the Signature 900 line.
Lowe's $2,098$2,098
Prices were last checked October 21, 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 Ariston NUOS Side-Connect 40 Gal for hot water (66 gallons in the first hour vs 55 gallons in the first hour) and cold rooms (heat pump runs down to 35 °F room air vs heat pump runs down to 37 °F room air).
- Choose the A.O. Smith Voltex MAX 40 Gal for noise (45 dB(A) vs 49.1 dB(A)).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every 40–50 gallon heat pump water heater; a clear win is highlighted. How we rank explains each one.
| Factor weight | Ariston NUOS Side-Connect 40 Gal | A.O. Smith Voltex MAX 40 Gal |
|---|---|---|
| Overall rating | 3.3/5 | 3.1/5 |
| Efficiency 35% | 41 3.58 UEF | 43 3.60 UEF |
| Hot water 20% | 64 66 gallons in the first hour | 20 55 gallons in the first hour |
| Warranty 20% | 70 10-year tank, 10-year parts | 75 10-year tank, 10-year parts, 1-year labor |
| Cold rooms 15% | 40 heat pump runs down to 35 °F room air | 32 heat pump runs down to 37 °F room air |
| Noise 10% | 43 49.1 dB(A) | 69 45 dB(A) |
Specifications
| Ariston NUOS Side-Connect 40 Gal | A.O. Smith Voltex MAX 40 Gal | |
|---|---|---|
| Ratings (ENERGY STAR) | ||
| Size (nominal) | 40 gal | 40 gal |
| Tank volume (measured) | 37 gal | 36 gal |
| Uniform Energy Factor | 3.58 | 3.60 |
| First-hour rating | 66 gal | 55 gal |
| Draw pattern | Medium | Medium |
| Yearly energy use | 907 kWh | 902 kWh |
| Heat pump cut-off (low) | 35 °F | 37 °F |
| Sound level | 49.1 dB(A) | 45 dB(A) |
| ENERGY STAR ID | 3942613 | 3417480 |
| Installation | ||
| Power | 240 V | 240 V |
| Circuit | 30 A, 208/240 V | 30 A, 208/240 V |
| Backup element | 4,500 W | 4,500 W |
| Operating air range | 36 to 120 °F | 37 to 120 °F |
| Minimum room size | 700 cu ft | 450 cu ft |
| Size | 37.6 in tall, 18.2 in across | 66 in tall, 20 in across |
| Weight | - | 191 lb |
| Refrigerant | R-134a | R-134a |
| Features | ||
| Wi-Fi | Built in | Built in |
| App | Ariston NET | A. O. Smith (iCOMM) |
| Demand response port (CTA-2045) | Yes | Yes |
| Leak detection | Yes | Yes |
| Modes | Comfort, Green, Fast, Electric, Vacation | Hybrid, Heat Pump, Hot Water+ (3 levels), Guest, Electric, Vacation |
| Warranty and models | ||
| Warranty | 10 yr tank, 10 yr parts | 10 yr tank, 10 yr parts, 1 yr labor |
| Also sold as | American Standard ASHPWH-40*****, Lennox WHHP040T45MD240S**** | American HPA10240H045DV, Lochinvar HPPA040KD, Reliance 10-40-DHPTA, State HPAX-40-DHPT |
| Released | 2024-12 | 2024-03 |