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 2.4. The Ariston NUOS Side-Connect 40 Gal leads on efficiency and hot water.
Rheem ProTerra Plug-in 40 Gal
#23 in 40–50 GallonFull review
A plug-in for replacing a gas tank in a mild-climate garage or basement without new wiring. Buy a size up, since it has no element to fall back on.
Home Depot $1,699$1,699
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 efficiency (3.58 UEF vs 2.80 UEF) and hot water (66 gallons in the first hour vs 45 gallons in the first hour).
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 | Rheem ProTerra Plug-in 40 Gal |
|---|---|---|
| Overall rating | 3.3/5 | 2.4/5 |
| Efficiency 35% | 41 3.58 UEF | 0 2.80 UEF |
| Hot water 20% | 64 66 gallons in the first hour | 0 45 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) | 50 noise not published (neutral score used) |
Specifications
| Ariston NUOS Side-Connect 40 Gal | Rheem ProTerra Plug-in 40 Gal | |
|---|---|---|
| Ratings (ENERGY STAR) | ||
| Size (nominal) | 40 gal | 40 gal |
| Tank volume (measured) | 37 gal | 36 gal |
| Uniform Energy Factor | 3.58 | 2.80 |
| First-hour rating | 66 gal | 45 gal |
| Draw pattern | Medium | Low |
| Yearly energy use | 907 kWh | 780 kWh |
| Heat pump cut-off (low) | 35 °F | - |
| Sound level | 49.1 dB(A) | - |
| ENERGY STAR ID | 3942613 | 3555260 |
| Installation | ||
| Power | 240 V | Plug-in 120 V |
| Circuit | 30 A, 208/240 V | Shared 15 A or 20 A circuit |
| Backup element | 4,500 W | None |
| Operating air range | 36 to 120 °F | 37 to 145 °F |
| Minimum room size | 700 cu ft | 700 cu ft |
| Size | 37.6 in tall, 18.2 in across | 62.3 in tall, 20.3 in across |
| Weight | - | 157 lb |
| Refrigerant | R-134a | R-134a |
| Features | ||
| Wi-Fi | Built in | Built in |
| App | Ariston NET | EcoNet |
| Demand response port (CTA-2045) | Yes | Yes |
| Leak detection | Yes | No |
| Modes | Comfort, Green, Fast, Electric, Vacation | Heat Pump, 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**** | Friedrich PROH40 T0 FD120-M, Friedrich PROH40 T0 FD120-MSO, Rheem PROPH40 T0 RH120-M, Rheem PROPH40 T0 RH120-MSO, Richmond 10E40-HP120M, Richmond 10E40-HP120MS, Ruud PROUH40 T0 RU120-M, Ruud PROUH40 T0 RU120-MSO |
| Released | 2024-12 | 2022-04 |