A tankless water heater can provide hot water without keeping a storage tank heated, but the right size depends on how many fixtures you use at once and how cold your incoming water gets.
These 10 options span compact electric units, higher-output electric models, and indoor or outdoor gas heaters. Use the buying guide below to narrow the field before checking installation requirements.
Best 10 On Demand Tankless Water Heaters Picks for 2026
Best Smart Electric Pick
Electrolux 14kW WiFi Tankless Water Heater
- Up to 3.4 GPM for one to two fixtures
- WiFi and Alexa temperature controls
- Needs a dedicated 240V/60A circuit
Best For: Small homes with suitable electrical capacity
Best Compact Natural Gas Pick
- 80,000 BTU; up to 3.6 GPM
- Activates at 0.53 GPM
- Requires licensed gas and vent installation
Best For: Small homes with natural gas
Best High-Flow Propane Pick
- Up to 6.8 GPM on propane
- Tuya app and circulation features
- Needs 120V power and appropriate piping
Best For: Propane homes with multiple hot-water outlets
Best Serviceable Electric Pick
- 18kW output; up to 4.4 GPM
- Field-serviceable copper elements
- Digital thermostat with self-modulation
Best For: 240V electric setups prioritizing serviceability
Compact Electric Pick
- 8 kW electric; listed 2 gpm flow
- Compact wall-mounted design
- Lifetime component warranty has exclusions
Best For: Compact installations with modest hot-water demand
Outdoor Gas Pick
- 7.0 gpm at a 35°F rise
- 160,000 BTU/hr natural-gas output
- Outdoor installation; professional setup required
Best For: Homes seeking higher-flow outdoor natural-gas heating
High-Power Electric Pick
- Up to 28.8 kW at 240 V
- Advanced Flow Control and two presets
- Requires three 40-amp breakers
Best For: Homes equipped for a high-power electric installation
Best for Higher Flow
Rheem RTEX-24 24kW Electric Tankless Water Heater
- Up to 5.9 GPM stated flow
- 80°F–140°F digital settings
- Recommended 200-amp household service
Best For: Higher-demand homes with sufficient electrical capacity
Best for Wi-Fi Control
WINTEMP WN18 18kW Electric Tankless Water Heater
- Up to 4.3 GPM stated flow
- Remote Wi-Fi temperature control
- Two 40-amp breakers required
Best For: Buyers who want remote control and have suitable electrical service
Best for Lower Flow Needs
Rheem RTEX-08 8kW Electric Tankless Water Heater
- Up to 1.95 GPM stated flow
- Compact wall-mounted design
- One 40-amp breaker required
Best For: Point-of-use or modest hot-water demand
Best Smart Electric Pick – Electrolux 14kW WiFi Tankless Water Heater
Among on demand tankless water heaters for smaller households, this Electrolux pairs a compact 14kW electric design with app and Alexa temperature controls. Its stated maximum flow is 3.4 GPM, and it is designed for one to two fixtures.
Best For: Apartments or small homes that want smart temperature control and have suitable 240V electrical capacity.
Pros:
- Adjustable 80–140°F temperature through WiFi app or Alexa voice control.
- Built-in scale inhibitor helps limit mineral buildup, including in hard-water areas.
- Compact 8.9 × 12.8 × 3.3-inch body saves wall space.
Cons:
- Requires a dedicated 240V/60A two-pole breaker, 6 AWG copper wiring, and a panel rated at least 150A.
- Its one-to-two-fixture design is not intended for heavy simultaneous demand.
The scale inhibitor and smart controls distinguish this unit, but check your electrical panel and expected fixture use before choosing it.
Best Compact Natural Gas Pick – APUS 80,000 BTU Indoor Heater
If you are comparing on demand tankless water heaters for a smaller home with natural gas, this 80,000 BTU APUS model offers a stated maximum of 3.6 GPM. Its 0.53 GPM activation flow also accommodates lighter draws.
Best For: One- to two-person homes that need natural-gas hot water for a shower, sink, and occasional second fixture.
Pros:
- Temperature controls and sensors are specified to hold the selected setting within ±1°F.
- Wall-mounted design saves floor space; an LED display shows the set temperature.
- Includes freeze, overheat, and flame-failure safeguards.
Cons:
- Gas, venting, and combustion setup require licensed installation.
- Limited 3.6 GPM maximum may not suit several high-demand fixtures running together.
This is a practical gas option for modest demand, provided your installation location has suitable venting and you account for professional setup.
Best High-Flow Propane Pick – APUS 140,000 BTU WiFi Heater
For households comparing on demand tankless water heaters with propane fuel, this indoor APUS model offers a stated maximum of 6.8 GPM and 140,000 BTU output. Its built-in circulation features and Tuya app controls add convenience for homes with several hot-water outlets.
Best For: Propane-supplied homes seeking higher flow, remote controls, and a circulation-based approach to reducing cold-water wait time.
Pros:
- Up to 6.8 GPM supports more simultaneous demand than the smaller models in this roundup.
- Tuya app lets you adjust the 95–140°F setting, preheat, and check status.
- Includes a booster pump and zero-cold-water piping accessories.
Cons:
- Circulation setup needs appropriate piping; a 120V AC supply powers its controls and pump.
- Must be completely drained during extended exposure near or below 41°F or prolonged non-use to avoid freeze damage.
Its high-flow rating and circulation hardware make it the more ambitious propane choice here, but plan the plumbing and electrical connections before buying.
Best Serviceable Electric Pick – Rheem RTEX-18 18kW Heater
This Rheem is a straightforward electric option among on demand tankless water heaters: its 18kW output self-modulates to match demand, with a stated maximum flow of 4.4 GPM. An external digital thermostat makes the set temperature easy to see and adjust.
Best For: Buyers who want a 240V electric unit with replaceable heating components and simple on-unit controls.
Pros:
- Self-modulation adjusts power use to hot-water demand.
- Digital LED temperature control is specified for ±1-degree accuracy.
- Two copper immersion heating elements are field-serviceable.
Cons:
- Requires a suitable 240V electrical installation for its 18kW load.
- No WiFi or remote-control features are listed.
Choose this model for conventional controls and serviceable elements, while sizing it against your incoming water temperature and simultaneous fixture needs rather than relying on peak GPM alone.
Compact Electric Pick – EcoSmart ECO 8
The EcoSmart ECO 8 is a compact option among on demand tankless water heaters, rated at 8 kW and 2 gpm. Its wall-mounted design measures about 8 inches wide, 11.5 inches high, and 4 inches deep.
Best For: Buyers seeking a compact electric heater with a modest listed flow rate.
Pros:
- Compact, 4.8-pound wall-mounted unit.
- Listed 99.8% efficiency and LED display.
- Lifetime warranty on electronics, heat exchanger, and element, subject to stated coverage limits.
Cons:
- Listed 2 gpm flow rate may not suit multiple simultaneous uses.
- Warranty does not cover labor or incidental damages.
The ECO 8 is worth considering when space is tight and your hot-water demand fits its listed output. Check that its 240-volt, 8-kW electrical requirements suit your installation.
Outdoor Gas Pick – Rheem RTG 7.0 GPM
For households comparing higher-output on demand tankless water heaters, the outdoor Rheem RTG runs on natural gas and is rated at 7.0 gpm at a 35°F temperature rise. Its 160,000 BTU/hr output is intended for whole-house use.
Best For: Homes needing an outdoor natural-gas unit for multiple hot-water demands.
Pros:
- Rated for 7.0 gpm at a 35°F temperature rise.
- Outdoor installation eliminates the need for indoor venting.
- Digital temperature control and built-in freeze protection.
- 15-year heat-exchanger and 5-year parts warranties.
Cons:
- Requires natural gas and outdoor installation.
- Professional installation is required.
This model is the higher-flow choice in this group, but its rated flow depends on the specified temperature rise. Confirm that your gas supply, climate, and installation site are suitable.
High-Power Electric Pick – Stiebel Eltron Tempra 29 Plus
The Stiebel Eltron Tempra 29 Plus is a high-power electric choice among on demand tankless water heaters. It draws up to 28.8 kW at 240 volts, mounts on a wall, and requires no venting.
Best For: Buyers with the specified electrical capacity who want a wall-mounted electric unit.
Pros:
- On-demand heating in a space-saving, vent-free design.
- Advanced Flow Control and two temperature memory presets.
- Listed 28.8-kW output at 240 volts.
Cons:
- Requires three dedicated 40-amp breakers, 8-gauge copper wiring, and at least 200-amp residential service.
- Listed flow rate is 3 gpm; suitability depends on hot-water demand.
The Tempra 29 Plus offers substantial electric heating capacity, but its electrical requirements are a major buying consideration. Verify service capacity and expected flow before choosing it.
Best for Higher Flow – Rheem RTEX-24 24kW Electric Tankless Water Heater
Among on demand tankless water heaters, the Rheem RTEX-24 is a higher-output electric option rated for up to 5.9 GPM. Its compact, wall-mounted design can free up floor space, but available flow depends on proper sizing for your home’s water-temperature needs.
Best For: Households seeking an electric unit for multiple fixtures that can accommodate its substantial electrical requirements.
Pros:
- 24kW output with a stated maximum flow of 5.9 GPM.
- Digital temperature adjustment in 1°F increments from 80°F to 140°F.
- Heats water only when needed and requires no gas venting.
Cons:
- Requires three 40-amp double-pole breakers, three sets of #8 AWG copper conductors with ground, and a recommended minimum 200-amp household service panel.
- The stated maximum flow may not be achievable in every climate or at every desired temperature.
Choose this model for its higher listed flow, not just its small footprint. Have a qualified professional verify both electrical capacity and expected hot-water demand before installation.
Best for Wi-Fi Control – WINTEMP WN18 18kW Electric Tankless Water Heater
The WINTEMP WN18 adds remote Wi-Fi temperature control to the on demand tankless water heaters in this roundup. Its 18kW, 240V design is rated for up to 4.3 GPM, while self-modulating operation adjusts power use to water flow and incoming temperature.
Best For: Buyers who want app-accessible temperature adjustments and whose expected hot-water use fits an 18kW electric unit.
Pros:
- Wi-Fi control lets you adjust the temperature remotely.
- Self-modulating operation adjusts power consumption as conditions change.
- ETL certified, with listed leakage, overheat, and dry-fire protections.
Cons:
- Requires two 40-amp double-pole breakers and two 8/2 AWG wiring runs; a 150-amp household service is recommended.
- Its 4.3 GPM figure is a maximum, so fixture capacity depends on incoming water temperature and demand.
The Wi-Fi feature is useful if the heater will be installed out of easy reach. Before buying, check the required wiring and ask a qualified electrician whether your service can support the unit.
Best for Lower Flow Needs – Rheem RTEX-08 8kW Electric Tankless Water Heater
The Rheem RTEX-08 is the smallest-output option among these on demand tankless water heaters. Rated for up to 1.95 GPM, this 8kW, 240V model is worth considering for a limited hot-water load rather than assuming it can supply a full household at once.
Best For: Point-of-use or modest hot-water needs that match its stated flow capacity.
Pros:
- Compact wall-mounted design saves floor space.
- Digital temperature control adjusts in 1°F increments from 80°F to 140°F.
- Heats water when a hot-water tap is turned on rather than maintaining a storage tank.
Cons:
- Maximum stated flow is 1.95 GPM, limiting simultaneous-use potential.
- Requires a 40-amp double-pole breaker, #8 AWG copper conductors with ground, and a recommended minimum 100-amp household service panel.
Although Rheem lists multiple-fixture applications, the modest maximum flow makes careful sizing especially important. Confirm the expected flow at your incoming water temperature before choosing it for more than one outlet.
How We Picked the Best On Demand Tankless Water Heaters
We selected a mix of electric, natural gas, and propane models to cover different homes and installation situations. The lineup includes lower-power electric choices for limited demand, larger electric units, and gas models with higher advertised flow rates. We compared stated power or BTU input, listed maximum GPM where available, fuel type, placement, and useful features such as Wi-Fi controls. Those specifications help narrow your options, but they do not replace a hot-water demand calculation or an installer’s assessment.
Quick Comparison
For modest hot-water needs, the 8 kW EcoSmart ECO 8 and Rheem 8 kW are places to start. The 14 kW Electrolux and 18 kW electric models sit in the middle of this selection. The 24 kW Rheem RTEX-24 and 28.8 kW Stiebel Eltron Tempra 29 Plus offer more electric heating power, subject to the available electrical service. If you need a gas model, the selection includes an 80,000 BTU indoor natural gas APUS, a 140,000 BTU indoor propane APUS, and a 160,000 BTU outdoor natural gas Rheem. Compare their published performance at your required temperature rise rather than treating headline GPM figures as directly interchangeable.
Key Buying Factors for On-Demand Tankless Water Heaters
Flow Rate and Temperature Rise
Add the flow rates of the fixtures you expect to run simultaneously, then determine the temperature rise from your cold-water inlet to your desired hot-water temperature. Colder inlet water makes any heater work harder and can reduce delivered GPM. A shower-plus-sink household needs a different setup from a home running multiple showers at once.
Fuel and Installation
Large electric models may require multiple dedicated 240 V circuits and substantial panel capacity; verify breaker, wire, and service requirements before buying. Gas units require the correct fuel supply and compliant venting where applicable. An outdoor-rated model is not a substitute for an indoor unit, and an indoor gas model needs installation that meets its specified venting rules. Check local codes and budget for professional installation.
Operating Costs and Upkeep
Compare local electricity, natural gas, and propane prices, not just the purchase price. Hard water can cause scale buildup, so check maintenance recommendations and consider water treatment if needed. Smart controls add convenience, but adequate capacity matters more than app connectivity.
Who Should Buy Which On Demand Tankless Water Heaters?
Choose a compact 8 kW electric model if your calculated demand and inlet temperature support it; do not assume it can serve a whole home. Consider the 14–18 kW electric choices for moderate demand when your panel can accommodate them, or the 24–28.8 kW units when you need more electric heating power and have suitable service. For higher simultaneous demand, compare the gas models against your temperature-rise requirements and existing fuel supply. Pick propane only if it fits your home’s fuel setup, and choose the outdoor Rheem only where its placement and climate requirements can be met.
