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RateLab Home Improvement & Tools Tankless Water Heaters

Best Tankless Water Heaters

Updated

We reviewed tankless water heaters across fuel type, flow rate, energy efficiency, install complexity, and long-term reliability. The category covers natural gas, propane, and electric models across point-of-use and whole-house applications -- a wide range of products united by the same core promise of on-demand hot water without a storage tank.

The detail most often overlooked is whether your home's existing infrastructure can support the heater you want. Natural gas and propane tankless heaters require a larger gas line than a storage tank heater, and most installations need a new dedicated gas run. Electric whole-house tankless heaters require 100-150 amps of dedicated electrical service -- a demand that exceeds many homes' total remaining capacity. Budget for a licensed plumber or electrician assessment before purchasing any whole-house model if you are replacing a storage tank setup.

Flow rate in gallons per minute is the primary sizing spec. A single bathroom shower uses roughly 1.5-2 GPM. A whole-house system needs to cover simultaneous demand -- two showers, a dishwasher, and a washing machine -- which typically requires 6-8+ GPM in cold climates. Undersizing is the most common installation mistake. Match the unit's rated flow to your household's peak demand in the coldest months, not average usage.

Quick picks

Use this table for the fastest answer, or jump into the full review cards below.

Pick Best for Verdict Review
Best OverallRinnai V53DeP Homes on propane that want a proven, serviceable whole-house tankless, Buyers replacing a 40-50 gallon propane storage tank with on-demand hot water Buy Read review
Best Gas OutdoorRheem RTG-84 Outdoor Homes on natural gas that want the simplest install path -- no interior venting, Households with 3-4 bathrooms that need full simultaneous-demand coverage Buy Read review
Best ElectricStiebel Eltron Tempra 20 Plus Homes without natural gas that want a whole-house on-demand electric solution, Buyers in warmer climates where groundwater enters above 55°F -- electric efficiency shines at lower temperature rises Buy Read review
Best High-EfficiencyRheem IKONIC Indoor High-usage households where maximum efficiency justifies the install premium over a non-condensing unit, Buyers in California and other low-NOx regulated markets where ultra-low NOx certification is required Consider Read review
SkipEcoSmart ECO 36 New construction with 400A service and planned dedicated capacity for electric water heating, Commercial or multi-family applications with engineered electrical infrastructure Skip Read review

Best Tankless Water Heaters

Best Overall

Rinnai V53DeP Propane Tankless Water Heater

The Rinnai V53DeP is the most reliable propane tankless water heater at this price point. With a 5.3 GPM flow rate and direct-vent configuration, it handles whole-house demand for households with 2-3 bathrooms in moderate climates. Rinnai's service network and parts availability make long-term ownership far less stressful than off-brand alternatives. The buy verdict reflects consistent performance, a proven track record, and real buyer satisfaction at the 466-review mark.

Buy
TL;DR

Strong feedback from Amazon buyers

Pros

  • Strong feedback from verified Amazon buyers
  • Rinnai's parts availability and service network are unmatched in tankless
  • Direct-vent design is flexible for indoor or outdoor placement
  • 5.3 GPM covers most whole-house demand in moderate climates
  • Precise digital temperature controls

Cons

  • Requires a licensed plumber and gas line upgrade for most installs
  • 5.3 GPM may fall short for large households or cold climate groundwater
  • Higher upfront cost than storage tank heaters -- payback period is typically 3-5 years
Verdict: Buy Full Review Check current price

Best Gas Outdoor Tankless

Best Gas Outdoor

Rheem RTG Series 8.4 GPM Natural Gas Tankless Water Heater Outdoor

The Rheem RTG Series 8.4 GPM outdoor unit is the cleanest install path for whole-house natural gas tankless heating. Outdoor placement eliminates venting requirements entirely -- no pipe runs through walls, no condensate drainage in the mechanical room. The 8.4 GPM flow rate covers simultaneous demand across 3-4 bathrooms in moderate climates. The strong buyer feedback reflects genuinely satisfied buyers, and Rheem's parts ecosystem rivals Rinnai's for long-term serviceability.

Buy
TL;DR

Strong feedback from verified Amazon buyers

Pros

  • Strong feedback from verified buyers
  • Outdoor installation eliminates the cost and complexity of indoor venting
  • 8.4 GPM handles real whole-house simultaneous demand
  • Rheem's service and parts network is strong across the US
  • 180,000 BTU input maintains flow rate under high demand

Cons

  • Requires a covered outdoor location -- direct weather exposure can shorten lifespan
  • Not suitable for freezing climates without proper freeze protection
  • Professional gas line and installation required
Verdict: Buy Full Review Check current price

Best Electric Tankless

Best Electric

Stiebel Eltron Tempra 20 Plus Tankless Water Heater, 19.2kW

The Stiebel Eltron Tempra 20 Plus is the electric tankless water heater the industry keeps returning to as a benchmark. Made in Germany, the Tempra series uses Advanced Flow Control -- a technology that automatically reduces flow rate to maintain output temperature when demand spikes, rather than delivering lukewarm water. That single feature separates it from every budget electric alternative. Strong buyer feedback backs it up, provided the install is planned around its 80A circuit.

Buy
TL;DR

Strong feedback from Amazon buyers

Pros

  • Strong feedback from verified Amazon buyers
  • Advanced Flow Control is the best flow management technology in electric tankless
  • German build -- Stiebel Eltron makes the Tempra series in Germany
  • Self-modulating power draw -- uses only what is needed for demand
  • Compact unit fits in small mechanical rooms or closets

Cons

  • Requires an 80A dedicated 240V circuit -- significant electrical work for many homes
  • Flow rate in cold climates is limited by physics -- electric heat output is fixed at 19.2kW
  • Higher upfront cost compared to storage tank electric heaters
Verdict: Buy Full Review Check current price

Best High-Efficiency Gas Indoor

Best High-Efficiency

Rheem IKONIC 8.4 GPM Natural Gas Tankless Water Heater Indoor

The Rheem IKONIC is the most efficient natural gas tankless water heater in Rheem's lineup, using condensing technology to extract heat from exhaust gases and achieve a 0.96 UEF rating. That efficiency comes at a cost: condensing units require a PVC vent run and condensate drainage plumbing, adding installation complexity and expense over non-condensing alternatives. The consider verdict reflects that the RTG outdoor unit achieves 8.4 GPM with simpler installation for most buyers, and the IKONIC's efficiency premium is only cost-justified for high-usage households with long payback time horizons.

Consider
TL;DR

0.96 UEF -- among the highest efficiency ratings in gas tankless

Pros

  • 0.96 UEF -- the highest efficiency tier in residential gas tankless
  • Ultra-low NOx certification works in California and other restricted markets
  • Condensing technology recovers heat that non-condensing units waste
  • Indoor installation keeps the unit protected from weather
  • Smart diagnostics and remote monitoring capable

Cons

  • Condensing installation requires PVC venting and condensate drainage -- adds cost and complexity
  • Higher purchase price than comparable non-condensing units with the same GPM output
  • The efficiency gains over a non-condensing unit have a long payback period for most households
Verdict: Consider Full Review Check current price

Skip -- Electrical Requirements Are Unrealistic for Most Homes

Skip

EcoSmart ECO 36 Tankless Electric Water Heater, 36kW

The EcoSmart ECO 36 is a 36kW whole-house electric tankless heater with an 8 GPM flow rate that looks compelling on paper. The skip verdict comes from a single spec: it requires 150A of dedicated 240V service. A typical 200A home panel already has most of its capacity spoken for -- HVAC, electric range, electric dryer, and other major loads. Adding 150A for a water heater alone is not a circuit addition; it is a panel upgrade and potentially a service entrance upgrade. The Stiebel Eltron Tempra 20 Plus achieves comparable real-world household output at 80A.

Skip
TL;DR

Mixed-to-solid feedback from Amazon buyers

Pros

  • 36kW output can deliver high GPM if electrical infrastructure is available
  • Self-modulating technology reduces power draw at lower demand
  • Compact unit size for 36kW output

Cons

  • 150A dedicated service requirement exceeds available capacity in most existing homes
  • Mixed-to-solid buyer feedback, weaker than the Stiebel Eltron Tempra 20 Plus
  • Installation costs can exceed the unit price once a panel or service upgrade is factored in
  • Better-designed alternatives achieve comparable household output at half the electrical demand
Verdict: Skip Full Review Check current price

All Tankless Water Heaters reviews

The grid is generated from product data and is ready to paginate once the subcategory passes 20 products.

Tools / Tankless Water Heaters Buy

Rinnai V53DeP Propane Tankless Water Heater

The Rinnai V53DeP is the most reliable propane tankless water heater at this price point. With a 5.3 GPM flow rate and direct-vent configuration, it handles whole-house demand for households with 2-3 bathrooms in moderate climates. Rinnai's service network and parts availability make long-term ownership far less stressful than off-brand alternatives. The buy verdict reflects consistent performance, a proven track record, and real buyer satisfaction at the 466-review mark.

Read review →
Tools / Tankless Water Heaters Buy

Rheem RTG Series 8.4 GPM Natural Gas Tankless Water Heater Outdoor

The Rheem RTG Series 8.4 GPM outdoor unit is the cleanest install path for whole-house natural gas tankless heating. Outdoor placement eliminates venting requirements entirely -- no pipe runs through walls, no condensate drainage in the mechanical room. The 8.4 GPM flow rate covers simultaneous demand across 3-4 bathrooms in moderate climates. The strong buyer feedback reflects genuinely satisfied buyers, and Rheem's parts ecosystem rivals Rinnai's for long-term serviceability.

Read review →
Tools / Tankless Water Heaters Buy

Stiebel Eltron Tempra 20 Plus Tankless Water Heater, 19.2kW

The Stiebel Eltron Tempra 20 Plus is the electric tankless water heater the industry keeps returning to as a benchmark. Made in Germany, the Tempra series uses Advanced Flow Control -- a technology that automatically reduces flow rate to maintain output temperature when demand spikes, rather than delivering lukewarm water. That single feature separates it from every budget electric alternative. Strong buyer feedback backs it up, provided the install is planned around its 80A circuit.

Read review →
Tools / Tankless Water Heaters Consider

Rheem IKONIC 8.4 GPM Natural Gas Tankless Water Heater Indoor

The Rheem IKONIC is the most efficient natural gas tankless water heater in Rheem's lineup, using condensing technology to extract heat from exhaust gases and achieve a 0.96 UEF rating. That efficiency comes at a cost: condensing units require a PVC vent run and condensate drainage plumbing, adding installation complexity and expense over non-condensing alternatives. The consider verdict reflects that the RTG outdoor unit achieves 8.4 GPM with simpler installation for most buyers, and the IKONIC's efficiency premium is only cost-justified for high-usage households with long payback time horizons.

Read review →
Tools / Tankless Water Heaters Skip

EcoSmart ECO 36 Tankless Electric Water Heater, 36kW

The EcoSmart ECO 36 is a 36kW whole-house electric tankless heater with an 8 GPM flow rate that looks compelling on paper. The skip verdict comes from a single spec: it requires 150A of dedicated 240V service. A typical 200A home panel already has most of its capacity spoken for -- HVAC, electric range, electric dryer, and other major loads. Adding 150A for a water heater alone is not a circuit addition; it is a panel upgrade and potentially a service entrance upgrade. The Stiebel Eltron Tempra 20 Plus achieves comparable real-world household output at 80A.

Read review →

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