Rheem ProTerra 40 Gal
#13 in 40–50 GallonFull review
A strong 240 V choice with Wi-Fi, widely stocked at Home Depot. GE Profile beats it on efficiency and noise.
Home Depot $2,098$2,098
The Rheem ProTerra 40 Gal is the better heat pump water heater overall, rated 3.4 to 3.3. The Rheem ProTerra 40 Gal leads on efficiency and noise. The Ariston NUOS Side-Connect 40 Gal wins on hot water and cold rooms.
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.
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 Rheem ProTerra 40 Gal for efficiency (3.83 UEF vs 3.58 UEF) and noise (45 dB(A) vs 49.1 dB(A)).
- Choose the Ariston NUOS Side-Connect 40 Gal for hot water (66 gallons in the first hour vs 60 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).
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 | Rheem ProTerra 40 Gal | Ariston NUOS Side-Connect 40 Gal |
|---|---|---|
| Overall rating | 3.4/5 | 3.3/5 |
| Efficiency 35% | 59 3.83 UEF | 41 3.58 UEF |
| Hot water 20% | 40 60 gallons in the first hour | 64 66 gallons in the first hour |
| Warranty 20% | 75 10-year tank, 10-year parts, 1-year labor | 70 10-year tank, 10-year parts |
| Cold rooms 15% | 32 heat pump runs down to 37 °F room air | 40 heat pump runs down to 35 °F room air |
| Noise 10% | 69 45 dB(A) | 43 49.1 dB(A) |
Specifications
| Rheem ProTerra 40 Gal | Ariston NUOS Side-Connect 40 Gal | |
|---|---|---|
| Ratings (ENERGY STAR) | ||
| Size (nominal) | 40 gal | 40 gal |
| Tank volume (measured) | 36 gal | 37 gal |
| Uniform Energy Factor | 3.83 | 3.58 |
| First-hour rating | 60 gal | 66 gal |
| Draw pattern | Medium | Medium |
| Yearly energy use | 859 kWh | 907 kWh |
| Heat pump cut-off (low) | 37 °F | 35 °F |
| Sound level | 45 dB(A) | 49.1 dB(A) |
| ENERGY STAR ID | 3554180 | 3942613 |
| 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 | 37 to 145 °F | 36 to 120 °F |
| Minimum room size | 700 cu ft | 700 cu ft |
| Size | 62.3 in tall, 20.3 in across | 37.6 in tall, 18.2 in across |
| Weight | 166 lb | - |
| Refrigerant | R-134a | R-134a |
| Features | ||
| Wi-Fi | Built in | Built in |
| App | EcoNet | Ariston NET |
| Demand response port (CTA-2045) | Yes | Yes |
| Leak detection | No | Yes |
| Modes | Energy Saver, Heat Pump, High Demand, Electric, Vacation | Comfort, Green, Fast, Electric, Vacation |
| Warranty and models | ||
| Warranty | 10 yr tank, 10 yr parts, 1 yr labor | 10 yr tank, 10 yr parts |
| Also sold as | Friedrich PROH40 T2 FD400-30, Friedrich PROH40 T2 FD400-SO, Rheem PROPH40 T2 RH375-30, Rheem PROPH40 T2 RH375-SO, Rheem PROPH40 T2 RH400-30, Rheem PROPH40 T2 RH400-SO, Richmond 10E40-HP530, Richmond 10E40-HP5S30, Richmond 10E40-HP5U30, Richmond 10E40-HP5US30, Ruud PROUH40 T2 RU375-30, Ruud PROUH40 T2 RU375-SO, Ruud PROUH40 T2 RU400-30, Ruud PROUH40 T2 RU400-SO | American Standard ASHPWH-40*****, Lennox WHHP040T45MD240S**** |
| Released | 2024-06 | 2024-12 |