A tankless water heater heats water only when you open a tap, so it never runs out mid-shower and wastes no energy keeping a tank hot. The right one depends on what powers your home: gas models deliver the highest flow for large households, while electric models are simpler to install and need no venting. These five are the best tankless water heaters we found for whole-house use.
We compared flow rate, fuel type, efficiency, controls and installation needs using manufacturer specifications and owner feedback. For scored comparisons see our tankless water heater reviews; our Editorial Policy explains our process. Gas units must be installed and vented by a licensed professional.
Top 3 Best Tankless Water Heaters
Rinnai RX180iN Condensing Smart Sense Tankless Water Heater
- 10 GPM
- Condensing
- Wi-Fi ready
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater
- 24kW
- 5.9 GPM
- No venting
Rheem RTG-95DVLN-3 9.5 GPM Natural Gas Tankless Water Heater (Indoor)
- 9.5 GPM
- 199,900 BTU
- 3–4 showers
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Best Tankless Water Heaters Compared
| # | Product | Key Features | |
|---|---|---|---|
| 1 |  Rinnai RX180iN Condensing Smart Sense Tankless Water Heater |
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| 2 |  Rheem RTG-95DVLN-3 9.5 GPM Natural Gas Tankless Water Heater (Indoor) |
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| 3 |  Rheem RTEX-24 24kW 240V Electric Tankless Water Heater |
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| 4 |  Stiebel Eltron Tempra 20 Plus 19.2kW Electric Tankless Water Heater |
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| 5 |  EcoSmart ECOS 18 18kW 240V Electric Tankless Water Heater |
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1. Rinnai RX180iN Condensing Smart Sense Tankless Water Heater
Best Overall
- Up to 10 GPM, about 6 fixtures at once
- Runs on natural gas or propane (Smart Sense)
- Condensing design, UEF 0.98
- Indoor or outdoor install with Versa Vent
- Quick Flush feature eases maintenance
- Needs gas line sizing and professional install
- Outdoor install needs a separate vent cap
- Fuel: natural gas or propane
- Flow: up to 10 GPM
- Model: RX180iN
The Rinnai RX180iN is the most flexible tankless heater we found: one model works on either gas type and indoors or out.
Its condensing design squeezes extra heat from exhaust, which is why its efficiency rating is so high.
Who the Rinnai RX180iN fits best
Homes with 2–3 bathrooms and gas service.
Who should skip the Rinnai RX180iN
Homes without gas or a suitable vent path.
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2. Rheem RTG-95DVLN-3 9.5 GPM Natural Gas Tankless Water Heater (Indoor)
Best for Large Families
- 9.5 GPM at a 35°F rise
- 199,900 BTU output for 3–4 showers
- UEF 0.82 non-condensing
- Direct vent for indoor install
- Natural gas only (this version)
- Non-condensing, slightly less efficient
- Fuel: natural gas
- Flow: 9.5 GPM
- Model: RTG-95DVLN-3
Rheem’s RTG 9.5 GPM is built for busy households where showers, laundry and the dishwasher run at once.
It is a common replacement for aging tank heaters.
Who the Rheem RTG 9.5 GPM fits best
Large families on natural gas.
Who should skip the Rheem RTG 9.5 GPM
Propane homes (choose the propane version).
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3. Rheem RTEX-24 24kW 240V Electric Tankless Water Heater
Best Electric
- 24kW gives up to 5.9 GPM
- Digital temperature control 80–140°F in 1° steps
- No venting or gas line
- About 99.8% energy efficient (per Rheem)
- Needs three 40A double-pole breakers
- 200A service recommended
- Power: 24kW, 240V
- Flow: up to 5.9 GPM
- Model: RTEX-24
The RTEX-24 is the strongest all-round electric pick, enough for two showers in warmer climates.
Check your panel first: it needs three dedicated circuits.
Who the Rheem RTEX-24 fits best
Electric homes in mild to moderate climates.
Who should skip the Rheem RTEX-24
Homes with 100A service.
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4. Stiebel Eltron Tempra 20 Plus 19.2kW Electric Tankless Water Heater
Best Premium Electric
- Advanced Flow Control keeps temperature steady
- 19.2kW self-modulating heating
- Digital display and savings monitor
- No venting, quiet operation
- Made in Germany
- Needs large breakers
- Flow drops slightly at peak demand by design
- Power: 19.2kW, 240V
- Model: Tempra 20 Plus
- Install: hardwired
Stiebel Eltron’s Advanced Flow Control slightly reduces flow when demand exceeds capacity, so the temperature never drops.
It is a refined, quiet unit.
Who the Stiebel Eltron Tempra 20 Plus fits best
Homes that value steady shower temperature.
Who should skip the Stiebel Eltron Tempra 20 Plus
Very cold climates needing high flow.
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5. EcoSmart ECOS 18 18kW 240V Electric Tankless Water Heater
Best Value Electric
- 18kW with self-modulating power
- Up to 4.4 GPM
- Holds temperature within about 1°F
- Compact, 90% smaller than a tank (per maker)
- Needs about 75A of breaker capacity
- Best for 1–2 showers at once
- Power: 18kW, 240V
- Flow: up to 4.4 GPM
- Model: ECOS 18
EcoSmart’s ECOS 18 is a straightforward electric choice for smaller homes and apartments.
Self-modulation draws only the power needed.
Who the EcoSmart ECOS 18 fits best
Small homes in warm climates.
Who should skip the EcoSmart ECOS 18
Large households.
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How to Choose a Tankless Water Heater
Gas or electric
Gas models deliver more GPM in cold climates but need venting and a gas line. Electric models need no venting but require large breakers and enough panel capacity.
Size by flow rate
Add up fixtures used at once: a shower uses about 2 GPM, a faucet about 1 GPM. Colder incoming water lowers real flow.
| Household | Typical need | Good fit |
|---|---|---|
| 1–2 people | 2–4 GPM | 18–24kW electric |
| 3–4 people | 5–7 GPM | Gas 140k–180k BTU |
| 5+ people | 8–11 GPM | Gas 180k–199k BTU |
Installation
Use a licensed plumber or electrician, follow local codes, and install CO alarms with gas units.
Frequently Asked Questions
Which tankless water heater is best overall?
The Rinnai RX180iN for its flow, efficiency and dual-fuel flexibility.
Is gas or electric tankless better?
Gas suits larger homes and cold climates; electric is simpler to install.
Do tankless water heaters need maintenance?
Yes, flush them regularly to remove scale, especially with hard water.
Can I install a tankless water heater myself?
Hire licensed pros for gas, venting and high-amp electrical work.
Final Verdict: Best Tankless Water Heater
The Rinnai RX180iN is the best tankless water heater overall. The Rheem RTEX-24 is the best electric choice, and the Rheem RTG 9.5 GPM is best for large families.
Overall: Rinnai RX180iN Condensing Smart Sense Tankless Water Heater Check Latest Price
Electric: Rheem RTEX-24 24kW 240V Electric Tankless Water Heater Check Latest Price
Large families: Rheem RTG-95DVLN-3 9.5 GPM Natural Gas Tankless Water Heater (Indoor) Check Latest Price
Size it right and you will never run out of hot water.
Looking for something else? Browse all of our Water Heaters guides and the wider Heating & Cooling section.
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