Rinnai REHP50
#4 in 40–50 GallonFull review
A Midea-built heater with Rinnai’s support network and one of the few listings on Amazon. Check the seller is a Rinnai-authorized dealer before buying.
Amazon $1,799 Lowe's $1,799$1,799
The Rinnai REHP50 is the better heat pump water heater overall, rated 3.6 to 3.5. The Rinnai REHP50 leads on hot water. The Ariston NUOS Side-Connect 50 Gal wins on cold rooms.
Ariston NUOS Side-Connect 50 Gal
#8 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 Rinnai REHP50 for hot water (73 gallons in the first hour vs 68 gallons in the first hour).
- Choose the Ariston NUOS Side-Connect 50 Gal for cold rooms (heat pump runs down to 35 °F room air vs heat pump runs down to 37.4 °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 | Rinnai REHP50 | Ariston NUOS Side-Connect 50 Gal |
|---|---|---|
| Overall rating | 3.6/5 | 3.5/5 |
| Efficiency 35% | 54 3.75 UEF | 54 3.75 UEF |
| Hot water 20% | 92 73 gallons in the first hour | 72 68 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% | 30 heat pump runs down to 37.4 °F room air | 40 heat pump runs down to 35 °F room air |
| Noise 10% | 44 49 dB(A) | 43 49.1 dB(A) |
Specifications
| Rinnai REHP50 | Ariston NUOS Side-Connect 50 Gal | |
|---|---|---|
| Ratings (ENERGY STAR) | ||
| Size (nominal) | 50 gal | 50 gal |
| Tank volume (measured) | 46 gal | 45 gal |
| Uniform Energy Factor | 3.75 | 3.75 |
| First-hour rating | 73 gal | 68 gal |
| Draw pattern | Medium | Medium |
| Yearly energy use | 844 kWh | 867 kWh |
| Heat pump cut-off (low) | 37.4 °F | 35 °F |
| Sound level | 49 dB(A) | 49.1 dB(A) |
| ENERGY STAR ID | 3531243 | 3942616 |
| 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 107 °F | 36 to 120 °F |
| Minimum room size | 700 cu ft | 700 cu ft |
| Size | 66.4 in tall, 21.7 in across | 45.8 in tall, 18.2 in across |
| Weight | 218 lb | - |
| Refrigerant | R-134a | R-134a |
| Features | ||
| Wi-Fi | No | Built in |
| App | - | Ariston NET |
| Demand response port (CTA-2045) | - | Yes |
| Leak detection | No | Yes |
| Modes | Economy, Heat Pump, Hybrid, E-Heater, 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 | - | American Standard ASHPWH-50*****, Lennox WHHP050T45MD240S**** |
| Released | 2024-08 | 2024-12 |