Tankless water heater sizing Last reviewed June 30, 2026

Electric vs Gas Tankless Water Heater: Which Size & Type?

By the WhatSize editorial team 4 min read Standards-reviewed

TL;DR

Gas tankless delivers 8–11 GPM (180k–250k BTU), lower operating cost ($250/yr). Electric delivers 3–8 GPM (18–36 kW), lower upfront ($500–$1,500). Real top units: Noritz NCC199CDV (199k BTU, 5.5 GPM, UEF 0.98); EcoSmart ECO 27 (27 kW electric, 6.5 GPM at 75°F rise).

Looking for a different size? See What Size Tankless Water Heater for a Family of 4? or browse all tankless water heater sizing guides.

Why electric vs gas tankless depends on your home's infrastructure

The electric vs gas tankless decision is driven by your home's existing infrastructure, the size of your household, and your tolerance for higher upfront cost vs lower operating cost.

Gas tankless (the whole-house default for 3+ person homes):

Top brand coverage per ENERGY STAR 2026: Rheem (91 models), Noritz (20), Takagi (16), Bradford White (13), Rinnai (10), Navien (6), Bosch (6)
Top picks: Noritz NCC199CDV (199k BTU, 5.5 GPM, UEF 0.98); Rinnai RU199iN (199k BTU, ~11 GPM at 35°F rise)
Requires gas line (1/2" — 3/4" upgrade for 199k+ BTU) + direct-vent or power-vent + condensate drain
Operating cost: $250/year (Fixr 2025)

Electric tankless (point-of-use + small household):

Standard sizes: 11, 13.5, 18, 24, 27, 36 kW
Top picks: Camplux TEW27 (27 kW, ~6.5 GPM at 75°F rise, $539); EcoSmart ECO 27 (27 kW, 6.5 GPM); Stiebel Eltron Tempra 29 Plus
Requires 200A service + 2–3 ×40A 240V breakers
Operating cost: $600/year (Fixr 2025) — 2.4×higher than gas per BTU in most US regions

For 3+ person whole-house use, gas wins on GPM capacity AND operating cost. Electric wins for point-of-use and 1–2 person homes without natural gas lines.

Top picks for this size

EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology #ad

★★★★ 4.1 · 5K+ · $244

Amazon

EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology, 17 x 17 x 3.5, White #ad

★★★★☆ 4.5 · 3K+ · $475

Amazon

Ecosmart ECO 24 24 KW at 240-Volt Electric Tankless Water Heater with Patented Self Modulating Technology, 17 x 17 x 3.5 #ad

★★★★☆ 4.7 · 337+ · $501

Amazon

Rheem 18kW 240V Tankless Electric Water Heater, Gray #ad

★★★★ 4.2 · 4K+ · $438

Amazon

Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray #ad

★★★★ 4.1 · 4K+ · $546

Amazon

Rheem 11kW 240V Tankless Electric Water Heater #ad

★★★★☆ 4.7 · 4K+ · $255

Amazon

Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY #ad

★★★★ 4.4 · 1K+ · $273

Amazon

Stiebel Eltron Tankless Water Heater – Tempra 29 Plus – Electric, 28.8kW, On Demand Hot Water, Eco, White, Made in Germany #ad

★★★★ 4.2 · 446+ · $695

Amazon

Stiebel Eltron Tankless Water Heater – Tempra 24 Trend – Electric, 24kW, On Demand Hot Water, Eco, White, Made in Germany #ad

★★★★ 4.2 · 90 · $620

Amazon

Rinnai V53DeN Natural Gas Tankless Water Heater - 5.3 GPM, Outdoor Installation #ad

★★★★ 4.2 · 230+ · $640

Amazon

Rinnai RE199iN Non-Condensing Natural Gas Tankless Water Heater, 199,000 BTU, 9.8 GPM On-Demand Hot Water, Indoor Whole House Installation #ad

★★★★ 4.2 · 39 · $1279

Amazon

EcoSmart ECOS 27 Tankless Electric Water Heater, 27 kW at 240 Volts, 112.5 Amps with Self Modulating Technology #ad

★★★★★ 5 · 13 · $420

Amazon

Rheem RTG-84XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Heater 8.4 GPM, 180,000 BTUs #ad

★★★★ 4.2 · 27 · $953

Amazon

Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Heater, 7.0 GPM, Gray #ad

★★★★ 4.2 · 63 · $804

Amazon

Electric Tankless Water Heater SIVUATEK 24kW, 240V - On-Demand Hot Water for Whole House - ETL Certified, Self Modulating - Compact Design for Easy Installation - for 4 Point of Use Hot Water #ad

★★★★ 4.3 · 250+ · $275

Amazon

Ranein 18kW Electric Tankless Water Heater, 240V On Demand Instant Endless Water Heater with LED Temperature Display, Control Knob, Space Saving Design, Up to 4.3 GPM for Whole House Water #ad

★★★★ 4.4 · 361+ · $208

Amazon

Rheem 6.5kW 240V Point of Use Thermostatic Tankless Electric Water Heater #ad

★★★★ 4.2 · 4K+ · $189

Amazon

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 #ad

★★★★ 4.2 · 137+ · $1533

Amazon

NEW Rinnai RXP199iN Smart Sense Condensing Tankless Water Heater, 199,000 BTU, Up to 11.1 GPM, Natural Gas or Propane, Indoor/Outdoor Installation, Built-In Recirculation Pump #ad

★★★★ 4.2 · 116+ · $1861

Amazon

Ranein Propane Gas Tankless Water Heater, Indoor Max 3.6 GPM, 80,000 BTU Instant Hot Water Heater #ad

★★★★ 4.4 · 618+ · $254

Amazon

A. O. Smith Tankless Water Heater Natural Gas - Endless Instant Hot Water up to 10 GPM - Integrated Recirculation Pump - Indoor Condensing 199,000 BTU ProLine® XE ATI-540P-N #ad

★★★★☆ 4.9 · · $1160

Amazon

A. O. Smith Tankless Water Heater - Natural Gas - 160,000 BTU - Endless Hot Water - Ultra-Low NOx - X3™ Scale Prevention - ProLine® XE ATI-240HX3-N #ad

★★★★☆ 4.9 · · $1300

Amazon

Electric Tankless Water Heater WINTEMP 27kW 240V, Whole House Hot Water Supply, On Demand Instant Endless Water Heater, with LED Temperature Display, WiFi Control, Up to 6.3 GPM, ETL Certified #ad

★★★★ 4.1 · 251+ · $340

Amazon

A. O. Smith Tankless Water Heater Natural Gas - Endless Instant Hot Water up to 10 GPM - Integrated Recirculation Pump - Indoor Condensing 199,000 BTU ProLine® XE ATI-540P-N #ad

★★★★ 4 · · $1160

Amazon

GASLAND Gasmart E 199,000 BTU Tankless Water Heater, Up to 7.6 GPM, CSA Certified Whole House Natural Gas Indoor Installation Residential On-demand Instant Hot Water Heater, CE686NG #ad

★★★★ 4.2 · 38 · $560

Amazon

Noritz GQ-C3261WX-FF US NG EZ Series Pro 11.1 GPM 199,900 BTU 120 Volt Residential Indoor/Outdoor Natural Gas Tankless Water Heater with Bluetooth Connectivity - Silver #ad

★★★★ 4.1 · 3 · $1799

Amazon

Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot Water, Smart WiFi, Compatible with Alexa & Google Home, ETL Certified IPX4, Space-Saving, Gray (APOLO-2.0 Upgrade) #ad

★★★★ 4.4 · 90 · $228

Amazon

Tankless Water Heater Natural Gas, 4.21 GPM 16L Indoor Instant Hot Water Heater with Digital Fahrenheit Display Multi-Protection Constant Temperature for Home & Apartment #ad

★★★★ 4.2 · 1 · $114

Amazon

These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.

When to choose electric vs gas

Natural gas available + 3+ person household: Gas tankless (180k–250k BTU) — Rinnai RU199iN or Noritz NCC199CDV.
No natural gas (rural, propane only): Either propane tankless (Bradford White RTGR150X1) or electric (Camplux TEW27).
1–2 person household, low usage: Electric point-of-use ($200–$500) or small whole-house (18–24 kW).
Tight budget: Electric is $500–$1,000 cheaper upfront but 2.4×more expensive to run.

Frequently asked questions

Is gas tankless better than electric?

For whole-house 3+ person households, yes — gas delivers 8–11 GPM vs electric 3–8 GPM, and gas operating cost is $250/year vs electric $600/year (Fixr 2025). Electric wins for point-of-use and 1–2 person homes. Real top units: Noritz NCC199CDV (gas, 5.5 GPM at 67°F rise, UEF 0.98) vs EcoSmart ECO 27 (electric, 6.5 GPM at 75°F rise).

Can I install electric tankless without 200A service?

Limited. Small electric units (11–18 kW, 2–3 GPM) can work on 100A service. Larger units (24+ kW) require 200A service and 2–3 ×40A 240V breakers. If your home has 100A service, a panel upgrade ($1,500–$3,000) is needed first.

Is electric tankless cheaper upfront?

Yes. Electric units cost $500–$1,500 vs gas $1,000–$2,500. Electric installation is also simpler (no gas line, no venting), often $500–$1,000 less than gas installation. Over the unit's lifetime, gas tankless saves money on operating cost ($250/yr vs $600/yr), with breakeven on the gas premium at ~6–10 years.

Does electric tankless need venting?

No. Electric tankless doesn't produce combustion gases, so no venting is needed. This is one of its main advantages — easier installation in spaces where venting isn't practical. Gas tankless requires direct-vent or power-vent plus condensate drain for high-efficiency condensing units.

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