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Best Whole House Electric Tankless Water Heater

3 expert-curated picks ranked by performance, value, and long-term reliability

Whole-house electric tankless water heaters serve homes without gas service that need continuous hot water across multiple fixtures. The category is constrained by household electrical service — most whole-house electric tankless requires 200A service to operate effectively. This list focuses specifically on what's practical for whole-house electric tankless installs.

Top whole-house electric tankless picks

Best for 200A service: EcoSmart ECO 27

27 kW, three 40A double-pole breakers, 113A continuous draw at 240V. Lifetime warranty on heat exchanger AND electronics. Stainless steel heat exchanger handles hard water 2× longer than copper. Capacity 3.0 GPM at a 60°F rise (cold-climate winter) or 4.5 GPM at a 40°F rise (Sun Belt). The most-installed whole-house electric tankless in the US. About $1,800 installed.

Best premium European: Stiebel Eltron Tempra 36 Plus

36 kW, requires 200A service with substantial headroom. The technically-best electric tankless on US market — quieter operation, smoother modulation, longer expected service life. 4.5 GPM at 60°F rise. About $2,400 installed.

Best Rheem option: Rheem RTEX-24

24 kW, 100A continuous draw across two 50A breakers. Rheem's national service network advantage. Lifetime heat-exchanger warranty. About $1,600 installed.

For 100A service with limited demand: Rheem RTEX-18

18 kW, 75A continuous on a single feed. Fits some 100A panels after load calculation. Works for single-shower-at-a-time use in warm climates. About $1,400 installed.

Electrical service is the bottleneck

Whole-house electric tanklessContinuous ampsMinimum service
EcoSmart ECO 18 / Rheem RTEX-1875A100A (with load calc) or 200A (clean)
EcoSmart ECO 24 / Rheem RTEX-24100A200A only
EcoSmart ECO 27113A200A only
Stiebel Eltron Tempra 36150A200A with substantial headroom

For homes with 100A service intending to install whole-house electric tankless, the math rarely works. Two paths:

  1. Service upgrade to 200A: $2,500-$4,500 typical. Adds significant cost but unlocks all electric tankless options.
  2. Switch to heat-pump tank: Rheem ProTerra uses only 30A 240V circuit. Fits any 100A panel. Lower operating cost than electric tankless. Almost always the better answer for 100A homes.

Climate sensitivity

Electric tankless capacity in GPM depends on temperature rise from groundwater to setpoint:

  • Sun Belt (groundwater 60-65°F): all whole-house electric tankless models perform at near-rated capacity.
  • Mid-Atlantic (groundwater 50°F): capacity reduced by ~20%. ECO 27 still works for 2-bath sequential demand.
  • Northeast/Midwest (groundwater 40-45°F): capacity reduced by ~40%. Even ECO 27 limited to single-shower-at-a-time use.

For northern climates, heat-pump tank is typically the better choice. For Sun Belt, electric tankless is competitive.

Install cost breakdown

Whole-house electric tankless install typically:

  • Unit cost: $549-$1,400
  • Breakers + wire + electrical labor: $400-$1,200 (heavy AWG wire and 2-3 high-amp breakers)
  • Plumbing for water connections: $150-$300
  • Permit: $75-$200
  • Total: $1,400-$3,000 installed
3 products
$949 – $1,795
Updated May 2026

Quick Comparison

# Product Brand Rating Price
1 Rinnai RU199iN Sensei Tankless Water Heater Rinnai 4.8 Check current price Amazon
2 Rheem Performance Platinum 50-Gallon Gas Water Heater Rheem 4.6 Check current price Amazon
3 AO Smith Signature Premier 50-Gallon Gas Water Heater AO Smith 4.5 Check current price Amazon