In these tankless water heater energy efficient reviews we score four efficient models, three condensing gas units and one self-modulating electric unit, on efficiency design, real flow, venting and running costs.
All four were scored on the same criteria using manufacturer specifications and owner feedback. For our shortlist see the best tankless water heater energy efficient guide; our Editorial Policy explains how we work.
Top 3 Efficient Tankless Heaters From Our Reviews
Noritz NRC66DVNG 6.6 GPM Indoor Condensing Tankless
- Condensing
- 6.6 GPM
- PVC vent
Stiebel Eltron Tempra 20 Trend 19.2kW Electric Tankless Water Heater
- Auto-modulation
- 19.2kW
- Silent
Ranein RH12KG-C 5.1 GPM Condensing Natural Gas Tankless
- 5.1 GPM
- Anti-freeze
- LED
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How We Scored Efficient Tankless Heaters
| Criterion | Weight | What we look at |
|---|---|---|
| Efficiency design | 35% | Condensing or modulation |
| Flow | 25% | GPM for the home |
| Venting and install | 20% | Plastic vent, breakers |
| Controls | 20% | Temperature control, display |
| Water heater | Score | Best for |
|---|---|---|
| Noritz NRC66DVNG | 8.7/10 | 2-bath gas homes |
| Stiebel Tempra 20 Trend | 8.5/10 | Electric homes |
| Ranein RH12KG-C | 8.2/10 | Value condensing |
| EZ Ultra HE | 7.8/10 | Small homes |
Efficient Tankless Heaters Compared
| # | Product | Key Features | |
|---|---|---|---|
| 1 |  Noritz NRC66DVNG 6.6 GPM Indoor Condensing Tankless |
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| 2 |  Stiebel Eltron Tempra 20 Trend 19.2kW Electric Tankless Water Heater |
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| 3 |  Ranein RH12KG-C 5.1 GPM Condensing Natural Gas Tankless |
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| 4 |  EZ Ultra HE Natural Gas Indoor Condensing Tankless Water Heater |
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1. Noritz NRC66DVNG 6.6 GPM Indoor Condensing Tankless
Highest Overall Score: 8.7/10
- Indoor condensing, high efficiency
- About 6.5–6.6 GPM
- Vents with Schedule 40 PVC
- Low NOx; remote thermostat included
- Limited listing detail
- Natural gas only
- Fuel: natural gas
- Model: NRC661-DV-NG
- Install: indoor
Noritz’s NRC66 scored highest for efficient condensing with simple PVC venting.
It suits 2-bath homes.
Who the Noritz NRC66DVNG fits best
2-bath natural gas homes.
Who should skip the Noritz NRC66DVNG
Propane homes.
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2. Stiebel Eltron Tempra 20 Trend 19.2kW Electric Tankless Water Heater
Best Electric: 8.5/10
- 19.2kW with auto-modulation
- No venting required
- Silent operation, digital display
- Copper heating system
- Large breakers needed
- Lower flow in cold climates
- Power: 19.2kW, 240V
- Model: Tempra 20 Trend
- Install: hardwired
The Tempra 20 Trend modulates power to each draw, so little energy is wasted.
It suits mild climates.
Who the Stiebel Eltron Tempra 20 Trend fits best
All-electric homes.
Who should skip the Stiebel Eltron Tempra 20 Trend
Cold northern homes.
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3. Ranein RH12KG-C 5.1 GPM Condensing Natural Gas Tankless
Best Value Condensing: 8.2/10
- Condensing, 120,000 BTU
- Up to 5.1 GPM, 2–3 bathrooms
- 95–149°F, anti-freeze
- Smart touch LED panel
- Newer brand
- Natural gas only
- Fuel: natural gas
- Flow: up to 5.1 GPM
- Model: RH12KG-C-NG
Ranein brings condensing efficiency at an accessible price.
Anti-freeze adds protection.
Who the Ranein RH12KG-C fits best
Budget-minded gas homes.
Who should skip the Ranein RH12KG-C
Large homes.
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4. EZ Ultra HE Natural Gas Indoor Condensing Tankless Water Heater
Compact Condensing: 7.8/10
- Condensing preheats water with exhaust
- Vents horizontally or vertically with 2″ PVC/CPVC
- Back-draft preventer included
- Digital display
- About 3.4 GPM at 45°F rise
- Small homes only
- Fuel: natural gas
- Model: EZ Ultra HE
- Flow: up to 3.4 GPM
EZ Ultra HE is a compact condensing unit for small homes and cabins.
Its flow is limited for multiple showers.
Who the EZ Ultra HE fits best
Small homes.
Who should skip the EZ Ultra HE
Families.
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Efficiency Checklist
- Prefer condensing gas units for the highest UEF.
- For electric, choose self-modulating models.
- Size correctly; oversizing wastes money.
- Flush yearly to keep efficiency up.
Frequently Asked Questions
Which efficient tankless heater scored highest?
The Noritz NRC66DVNG scored 8.7/10.
Do condensing units really save gas?
Yes, by reusing exhaust heat.
Is electric tankless efficient?
Yes, nearly all power becomes heat.
What venting do condensing units use?
Often PVC or CPVC, per the manual.
Final Verdict: Tankless Water Heater Energy Efficient Reviews
The Noritz NRC66DVNG is the best efficient tankless heater we scored. The Stiebel Tempra 20 Trend is the best electric unit, and the Ranein RH12KG-C is the best value condensing model.
Overall: Noritz NRC66DVNG 6.6 GPM Indoor Condensing Tankless Check Latest Price
Electric: Stiebel Eltron Tempra 20 Trend 19.2kW Electric Tankless Water Heater Check Latest Price
Value condensing: Ranein RH12KG-C 5.1 GPM Condensing Natural Gas Tankless Check Latest Price
Efficient heat today means lower bills tomorrow.
Looking for something else? Browse all of our Water Heaters guides and the wider Heating & Cooling section.
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