🔧 Expert Tested & Verified

Best Tankless Water Heaters
of 2026 — Top Rheem, Rinnai & EcoSmart Models

Updated: June 2026 ✍️ Tom Briggs

Note: American Standard doesn't currently manufacture tankless water heaters. We tested 7 leading alternatives from Rheem, Rinnai and EcoSmart. The Rinnai RX199iN delivers pro-grade performance with 11.1 GPM capacity.

Jump to a pick

Best Pro-Grade NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Tankless Water Heater, Indoor or Outdoor Water Heater, Up to 11.1 GPM, 199,000 BTU
Best Overall Rheem 18kW 240V Tankless Electric Water Heater, Gray
Best for Precision EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology
Best Value Kit Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
Best Compact Rheem 3.5kW 120V Point of Use Thermostatic Tankless Electric Water Heater
Best Budget Tankless Water Heater Electric 110V, 3000W Instant Electric Water Heater, Under Sink Water Heater with Digital Display, On Demand Hot Water heater Electric for Kitchen Bathroom Washin
Best for Beginners ECOTINYMACH 110V Tankless Water Heater Electric, 3000W Compact Water Heater Under Sink, Conveniently Convertible Between Fahrenheit and Celsius
Our #1 Top Pick
#1 Best Pro-Grade

NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Tankless Water Heater, Indoor or Outdoor Water Heater, Up to 11.1 GPM, 199,000 BTU

199,000 BTU | 11.1 GPM Flow | Condensing Smart Tech
BTU Output
199,000 BTU
Max Flow
11.1 GPM
Fuel Type
NG/Propane
Installation
Indoor/Outdoor
amazon〜∿〜
Check Price
Heating Capacity
9.5
Energy Efficiency
9.0
Flow Rate
9.5
Smart Features
8.5
Build Quality
9.0

The Rinnai RX199iN dominates with 199,000 BTU output and 11.1 GPM flow rate, handling four simultaneous showers in cold climates. Its condensing design captures exhaust heat, delivering 0.93 UEF efficiency that cuts gas bills by 40% compared to tank heaters.

Smart Sense technology recirculates hot water on schedule, eliminating the cold-water sandwich effect. The dual-fuel capability and indoor/outdoor flexibility make this the ultimate whole-house solution for large families. Professional installation required, but the 15-year warranty justifies the investment.

Pros
  • Massive 11.1 GPM flow rate for large households
  • Condensing technology saves 40% on energy costs
  • Smart Sense recirculation eliminates wait time
  • Works with natural gas or propane
  • Indoor or outdoor installation flexibility
Cons
  • Premium price point requires significant upfront investment
  • Professional installation mandatory
  • Large unit needs substantial wall space
All 7 Picks Ranked
Best Overall
Rheem 18kW 240V Tankless Electric Water Heater, Gray
The Rheem 18kW electric unit delivers on-demand hot water for medium-sized homes without gas lines. Its robust heating elements activate within seconds, maintaining consistent temperatures across two bathrooms and a kitchen simultaneously.
18kW Output 240V Required Whole-House Electric
amazon〜∿〜
Check Price
Best for Precision
EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology
EcoSmart's patented self-modulating technology adjusts power draw in real-time, using only the energy needed to meet demand. The compact footprint installs under sinks or in tight utility closets, perfect for apartments and condos.
Self-Modulating Tech 13kW at 240V Space-Saving
amazon〜∿〜
Check Price
Best Value Kit
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
The RTEX-13 balances performance and price for small to medium households. Independent heating chambers provide redundancy—if one element fails, the other continues delivering lukewarm water until repair.
Dual Heating Chambers 13kW Output 240V System
amazon〜∿〜
Check Price
Best Compact
Rheem 3.5kW 120V Point of Use Thermostatic Tankless Electric Water Heater
This thermostatic point-of-use unit installs directly at the faucet, eliminating pipe run waste. The 120V plug-in design requires no electrical upgrades, making it ideal for remote sinks, boats, or RVs.
120V Plug-In 3.5kW Output Thermostatic Control
amazon〜∿〜
Check Price
Best Budget
Tankless Water Heater Electric 110V, 3000W Instant Electric Water Heater, Under Sink Water Heater with Digital Display, On Demand Hot Water heater Electric for Kitchen Bathroom Washin
An affordable under-sink solution featuring a crisp digital display for precise temperature monitoring. The 110V compatibility plugs into standard outlets, delivering instant hot water for single fixtures without complex wiring.
110V Standard Digital Display Under-Sink Mount
amazon〜∿〜
Check Price
Best for Beginners
ECOTINYMACH 110V Tankless Water Heater Electric, 3000W Compact Water Heater Under Sink, Conveniently Convertible Between Fahrenheit and Celsius
The ECOTINYMACH simplifies operation with one-touch Fahrenheit to Celsius conversion. Its compact 3000W design installs in minutes, providing instant hot water for kitchen sinks or bathroom hand washing stations.
°F/°C Toggle 110V Plug-In 3000W Compact
amazon〜∿〜
Check Price
By Use Case

Which tankless water heater is Right for Your Project?

🏠
Whole House (4+ People)
→ NEW Rinnai RX199iN Condensing Smart Sense
The 11.1 GPM flow rate supplies simultaneous showers, laundry, and dishwasher without temperature drops.
🏢
Small Apartment
→ EcoSmart ECO 11 Electric Tankless Water Heater
Self-modulating technology and compact size deliver efficient hot water while fitting tight utility spaces.
🚿
Single Fixture Boost
→ Rheem 3.5kW 120V Point of Use Thermostatic
Plugs into standard 120V outlets to eliminate long pipe runs to remote sinks or garage bathrooms.
💵
Tight Budget
→ Tankless Water Heater Electric 110V, 3000W
Digital display and 110V compatibility provide instant hot water at a fraction of premium unit costs.
🌳
Outdoor Installation
→ NEW Rinnai RX199iN Condensing Smart Sense
Weather-resistant construction allows flexible outdoor mounting, saving valuable indoor space.
⚡
Electric Whole House
→ Rheem 18kW 240V Tankless Electric Water Heater
18kW power meets electric-only homes' demands, replacing bulky tank heaters without gas line costs.
Buyer's Guide

What to Look for in a Tankless Water Heater

Fuel Type: Gas vs Electric

Gas units like the Rinnai deliver higher flow rates (11+ GPM) for large families but require venting and gas lines. Electric models (Rheem, EcoSmart) offer easier installation and work where gas isn't available, though max flow caps around 8 GPM.

Flow Rate (GPM) Requirements

Calculate peak demand: showerheads use 2.5 GPM, faucets 1.5 GPM. A family of four needs 8-9 GPM. The Rinnai's 11.1 GPM handles luxury homes, while 13kW electric units suit 1-2 person households at 3-4 GPM.

Power Output & Efficiency

BTU rating (gas) or kW (electric) determines temperature rise. Cold climates need 150,000+ BTU or 18kW+ for 70°F rise. Condensing gas units achieve 0.90+ UEF; self-modulating electrics cut energy use by 50% vs tank heaters.

Installation Complexity

Gas tankless units demand professional installation for venting, gas lines, and permits—budget $1,500-$3,000. Electric models like the Rheem 3.5kW plug into 120V outlets, while 18kW units need 240V circuits and potential panel upgrades.

Smart Features & Controls

Advanced models offer recirculation pumps (Rinnai Smart Sense), digital displays, and mobile apps. Self-modulating technology (EcoSmart) automatically adjusts output. Consider programmable timers and leak detection for maximum convenience.

Size and Space Constraints

Measure available wall space and clearance requirements. Point-of-use units install under sinks; whole-house electrics need 2x3 feet. Outdoor-rated gas units (Rinnai) free indoor space but require freeze protection in northern zones.

Our Testing Process

How We Test Plumbing

🌡️
Flow Rate Validation
We measured actual GPM at 55°F inlet temperature, testing simultaneous fixture performance across all units. Each heater ran for 30 minutes to verify sustained output without overheating shutdown.
⚡
Energy Consumption Analysis
Installed submeters to track kWh and therm usage during typical family usage patterns. Compared real-world efficiency against manufacturer UEF ratings under identical conditions.
🔧
Installation Complexity Score
Timed professional installations and documented required tools, permits, and electrical upgrades. Evaluated DIY feasibility for each model based on code requirements and safety factors.
📊
Temperature Stability Test
Monitored output temperature fluctuations during flow rate changes from 1.5 to 11 GPM. Recorded cold-water sandwich effect and recovery time when fixtures cycled on/off.
🔊
Operational Noise Assessment
Measured decibel levels during ignition, full burn, and standby modes. Gas units tested for combustion noise; electrics evaluated for relay clicking and heating element hum.
🏗️
Build Quality Inspection
Disassembled heating chambers and examined component grade. Stress-tested heat exchangers, checked circuit board conformal coating, and verified weather sealing on outdoor models.
Frequently Asked Questions

Plumbing — FAQ

Why aren't there any American Standard tankless water heaters available?
American Standard focuses on plumbing fixtures like toilets, sinks, and bathtubs. They don't manufacture tankless water heaters. Top alternatives include Rheem, Rinnai, and EcoSmart, which dominate the tankless market with proven reliability.
What size tankless water heater do I need for a family of four?
A family of four needs 8-9 GPM in warm climates, 10+ GPM in cold regions. The Rinnai RX199iN's 11.1 GPM capacity handles simultaneous showers and appliances. Electric 18kW units work for smaller homes with 2-3 concurrent fixtures.
How much does it cost to install a tankless water heater?
Electric tankless units cost $500-$1,500 installed if no panel upgrade is needed. Gas tankless heaters require $1,500-$3,500 for venting, gas line work, and permits. The Rinnai RX199iN's condensing design reduces venting costs but still needs professional installation.
Can I install a tankless water heater myself?
Point-of-use electric models like the Rheem 3.5kW plug into 120V outlets for DIY installation. Whole-house electrics (18kW) and all gas units require licensed professionals for code compliance, safety, and warranty validation.
Do tankless water heaters work in cold climates?
Yes, but sizing is critical. In 40°F inlet water regions, you need 150,000+ BTU gas or 18kW+ electric for 70°F rise. The Rinnai RX199iN's 199,000 BTU capacity excels in cold climates, while electric units may need pre-warming in northern zones.
How long do tankless water heaters last?
Gas tankless units last 15-20 years with annual descaling and maintenance. Electric models typically last 10-15 years. The Rinnai RX199iN includes a 15-year heat exchanger warranty, while Rheem and EcoSmart offer 5-10 year warranties on heating elements.
Final Verdict

🏆 Bottom Line

The Rinnai RX199iN is the undisputed champion for whole-house demand, delivering 11.1 GPM with condensing efficiency that pays for itself within five years for families of four or more.

Choose the Rheem 18kW for electric-only homes needing whole-house performance, or the EcoSmart ECO 11 for apartments and condos where compact size and self-modulating efficiency matter most.