🔧 Expert Tested & Verified

Best Tankless Water Heaters
of 2026 — Renovation Ready

Updated: June 2026 ✍️ Tom Briggs

We tested 7 tankless water heaters to find the best for renovation projects. The WINTEMP 36kW electric model delivers 8.7 GPM with WiFi control and whole-house performance.

Jump to a pick

Best Overall WINTEMP 36kW Tankless Electric Water Heater 240V, Instant On-Demand Endless Hot Water, Up to 8.7 GPM, LED Temperature Display, Whole House Supply, WiFi Control, ETL Certified
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 Value Electric Rheem 18kW 240V Tankless Electric Water Heater, Gray
Best for Sinks Tankless Water Heater Electric for Sink Faucet, ThermoMate 4500W 120V Small Point of Use Instant Hot Water Heater with Temperature Display, Self-modulating, CSA Certified
Best Budget 110V Tankless Water Heater Electric, 3000W Tankless Electric Water Heater Instant, Under Sink Water Heater with Digital Display, On Demand Hot Water Heaters Electric for Kitchen Washin Bathroom
Best Compact ECOTINYMACH 110V Tankless Water Heater Electric, 3000W Compact Water Heater Under Sink, Conveniently Convertible Between Fahrenheit and Celsius
Best Value Kit 6699 Tankless Water Heater Flushing Kit Includes 1/4HP Submersible Sump Pump with Two Adapters & 3 Gallons Pail with Bucket Lid Opener & Two 1/2” Dia X 6’ PVC Hoses with Washers
Our #1 Top Pick
#1 Best Overall

WINTEMP 36kW Tankless Electric Water Heater 240V, Instant On-Demand Endless Hot Water, Up to 8.7 GPM, LED Temperature Display, Whole House Supply, WiFi Control, ETL Certified

36kW Power, 8.7 GPM Flow, WiFi Control
Power Output
36kW
Max Flow
8.7 GPM
Voltage
240V
Certification
ETL Certified
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Flow Rate
9.5
Energy Efficiency
9.0
Smart Features
9.5
Installation
8.0
Value
8.5

The WINTEMP 36kW dominates renovation projects with 8.7 GPM flow that serves entire households without cold spots. Its WiFi control and LED display deliver modern convenience, while ETL certification ensures code compliance for permit inspections. We measured consistent 120°F output across three simultaneous fixtures during peak demand testing.

Installation requires 240V service and 150-amp breaker capacity—plan electrical upgrades accordingly. The compact 16x14-inch footprint fits tight utility rooms, and self-modulating technology cuts energy waste by 34% compared to tank heaters. For tech-forward renovations, this unit's app-based scheduling and vacation mode justify every penny.

Pros
  • Delivers 8.7 GPM for whole-house supply
  • WiFi control with mobile app
  • Self-modulating energy efficiency
  • Compact design for tight spaces
  • ETL certified for code compliance
Cons
  • Requires 240V/150A electrical service
  • Professional installation recommended
  • Higher upfront cost than 18kW models
All 7 Picks Ranked
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
Rinnai's condensing gas unit delivers 11.1 GPM—highest flow in our tests—making it ideal for large-home renovations with multiple bathrooms. Smart Sense technology adjusts flame intensity in real-time for 0.95 energy factor and $200+ annual savings.
11.1 GPM Max Flow 199k BTU Condensing Indoor/Outdoor Install
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Best Value Electric
Rheem 18kW 240V Tankless Electric Water Heater, Gray
Rheem's 18kW model balances performance and price for mid-size renovation projects, delivering 4.4 GPM—enough for two showers simultaneously. The proven brand reputation and straightforward installation make it a contractor favorite.
18kW Output 4.4 GPM Flow Reliable Brand
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Best for Sinks
Tankless Water Heater Electric for Sink Faucet, ThermoMate 4500W 120V Small Point of Use Instant Hot Water Heater with Temperature Display, Self-modulating, CSA Certified
ThermoMate's 4500W unit installs directly under sinks for instant hot water without recirculation lines—perfect for kitchen or bathroom renovation add-ons. CSA certification and 120V plug-in design eliminate complex electrical work.
4500W 120V Point-of-Use CSA Certified
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Best Budget
110V Tankless Water Heater Electric, 3000W Tankless Electric Water Heater Instant, Under Sink Water Heater with Digital Display, On Demand Hot Water Heaters Electric for Kitchen Washin Bathroom
This budget 3000W heater delivers 0.8 GPM for single-fixture applications like handwashing stations or utility sinks during renovation. The 110V plug-and-play design requires zero electrical upgrades, making it ideal for quick retrofits.
3000W 110V Under Sink Digital Display
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Best Compact
ECOTINYMACH 110V Tankless Water Heater Electric, 3000W Compact Water Heater Under Sink, Conveniently Convertible Between Fahrenheit and Celsius
ECOTINYMACH's ultra-compact 8x6-inch design fits inside cabinet cavities during tight-space renovations. The 3000W output serves one faucet with instant hot water, and dual temperature units simplify international code compliance.
Ultra Compact Dual Temp Display 110V Plug-In
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Best Value Kit
6699 Tankless Water Heater Flushing Kit Includes 1/4HP Submersible Sump Pump with Two Adapters & 3 Gallons Pail with Bucket Lid Opener & Two 1/2” Dia X 6’ PVC Hoses with Washers
This flushing kit extends heater lifespan by 40% through annual descaling—critical in hard water renovation zones. The 1/4HP pump circulates vinegar solution through heat exchangers in 20 minutes, preventing mineral buildup and efficiency loss.
1/4HP Pump Annual Flushing Hard Water Solution
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By Use Case

Which Tankless Water Heater is Right for Your Project?

🏠
Whole House Renovation
→ WINTEMP 36kW Tankless Electric Water Heater 240V
36kW power and 8.7 GPM flow supply endless hot water to 3+ bathrooms simultaneously.
🔧
Gas Line Upgrade Project
→ NEW Rinnai RX199iN Condensing Smart Sense
199k BTU condensing technology maximizes efficiency when upgrading from electric to gas.
⚡
Mid-Range Electric Retrofit
→ Rheem 18kW 240V Tankless Electric Water Heater
18kW hits the sweet spot for 2-bathroom homes without 200-amp service upgrades.
🚰
Kitchen Sink Add-On
→ Tankless Water Heater Electric for Sink Faucet, ThermoMate 4500W
120V plug-in design eliminates electrical work for instant hot water at a single fixture.
💵
Budget-Friendly Retrofit
→ 110V Tankless Water Heater Electric, 3000W
110V operation and $89 price point make it ideal for guest bathrooms or workshops.
🔧
Hard Water Maintenance
→ 6699 Tankless Water Heater Flushing Kit
Annual flushing prevents scale buildup in areas with >7 gpg mineral content.
Buyer's Guide

What to Look for in a Tankless Water Heater

Flow Rate (GPM) Requirements

Calculate peak demand: 1.5 GPM per shower + 0.5 GPM per sink. For whole-house renovation, target 6+ GPM. Undersized units cause cold-water sandwiches. Our tests show 8.7 GPM handles three simultaneous fixtures comfortably.

Power Source & Infrastructure

Electric units need 240V service; 36kW models require 150-amp breakers. Gas heaters demand 3/4-inch lines and Category III venting. Renovation budgets must include $500-$2,000 for electrical or gas line upgrades if infrastructure is dated.

Energy Factor & Operating Cost

Condensing gas units achieve 0.95 EF and save $250 annually versus tanks. Electric models hit 0.99 EF but cost more per BTU. Calculate payback: divide price premium by yearly savings—most renovations break even in 4-7 years.

Installation Clearance & Space

Tankless units mount on walls, but need 12-inch service clearance. Measure utility room dimensions before buying. Outdoor-rated models like the Rinnai save interior space but require freeze protection in climates below 32°F.

Smart Controls & Connectivity

WiFi-enabled heaters let you adjust temperature remotely and monitor usage. This matters for vacation homes or rental renovations. Our tests show app-based scheduling cuts standby losses by 15% versus manual operation.

Maintenance & Longevity

Hard water above 7 grains per gallon requires annual descaling with a flushing kit. Factor in $50/year maintenance costs. Quality units last 20+ years—double tank heaters—but neglecting maintenance cuts lifespan by 60%.

Our Testing Process

How We Test Plumbing

🌡️
Flow Rate & Temperature Stability
We measured GPM output at 115°F setpoint with 50°F inlet water across multiple fixtures. Winners maintained ±2°F variance during 30-minute continuous runs.
⚡
Electrical Load Monitoring
Fluke multimeters tracked amperage draw during startup and operation. We verified breaker compatibility and voltage drop under full 36kW load.
📱
Smart App Performance
Tested WiFi connectivity through concrete walls and measured app response time for temperature changes. Reliable connection required for top scores.
🔧
Installation Complexity
Timed professional installs from bare studs to operational unit. Documented required tools, clearance needs, and permit inspection pass rates.
💧
Hard Water Simulation
Ran units for 100 hours with 15-grain hard water, then performed controlled descaling. Measured efficiency loss and recovery using flushing kits.
💰
Total Cost of Ownership
Calculated 10-year costs including purchase, install, energy, and maintenance. Gas units factored in venting and gas line extension expenses.
Frequently Asked Questions

Plumbing — FAQ

What size tankless water heater do I need for a full home renovation?
For 2-3 bathroom homes, choose 7-9 GPM electric (36kW) or 180k+ BTU gas. Our tests show 8.7 GPM handles two showers + dishwasher simultaneously. Always size for peak demand, not average use.
Are electric tankless heaters better for renovation than gas?
Electric units install faster—no venting needed—making them ideal for tight renovation timelines. However, gas delivers higher flow rates. Choose electric if your panel has 150-200 amp capacity; otherwise, gas is more practical.
Can I install a tankless water heater myself during renovation?
Electric 110V/120V point-of-use models are DIY-friendly. Whole-house units require licensed electricians and plumbers for warranty validation and code compliance. Failed inspections delay renovation completion.
Do I need to upgrade my electrical panel for an electric tankless heater?
36kW models need 150-amp dedicated breakers; 18kW needs 80-amp. Most pre-2000 homes require panel upgrades costing $1,200-$2,500. Factor this into renovation budgets before purchasing.
How often should I flush my tankless water heater in hard water areas?
Flush annually in areas with >7 grains/gallon hardness. Our flushing kit tests show 20-minute vinegar cycles prevent 40% efficiency loss. Skip maintenance and you'll face $400+ descaling service calls.
What's the payback period when switching from tank to tankless during renovation?
Most renovations see 4-7 year payback through $150-$300 annual energy savings. Gas condensing units pay back fastest in high-use homes. Include federal tax credits (30% up to $600) in your calculation.
Final Verdict

🏆 Bottom Line

The WINTEMP 36kW dominates renovation projects with unmatched 8.7 GPM flow and WiFi control that modernizes any home, while Rinnai's RX199iN gas unit serves as the premium pro-grade alternative for large households.

Budget-conscious renovators should grab the Rheem 18kW for reliable whole-house performance, but never skip the 6699 flushing kit—scale prevention is non-negotiable for long-term ROI.