Best Tankless Water Heater

A cold shower can turn a calm morning into a small household crisis. The right tankless water heater prevents that shock by heating water as you need it, without keeping dozens of gallons warm inside a large storage tank. Yet the word “tankless” does not mean every unit can feed every faucet at once. Power, incoming water temperature, fuel type, and household demand still set the limits.

The best tankless water heater for most larger homes is a high-output condensing gas model. These units can serve several bathrooms, recover quickly, and run at a lower fuel cost than many whole-house electric units. Electric models still make sense in warm regions, small homes, apartments, cabins, and properties where adding a gas line or vent would cost too much.

Best Tankless Water Heaters at a Glance

Best Overall: Rinnai RXP199iN

The Rinnai RXP199iN sits at the top of this list because it pairs strong output with a built-in recirculation pump. Its rated maximum flow is 11.1 gallons per minute, while its 199,000 BTU burner gives it enough muscle for a busy home. The 0.98 UEF rating also places it among the most efficient residential gas models.

Picture this heater as a compact engine mounted on the wall. It stays quiet until a faucet opens. The burner then wakes up and adjusts its output to match the demand. A kitchen faucet does not need the same firepower as two showers and a washing machine, so the unit changes its fuel use rather than running at full strength all day.

The internal pump can move hot water through a recirculation line. That can shorten the wait at distant bathrooms. It also cuts the amount of cold water that runs down the drain while someone waits for heat. Homes with long pipe runs gain the most from this feature.

The RXP199iN can run on natural gas or propane. It also permits indoor or outdoor mounting. That flexibility helps when a utility room has limited wall space or awkward vent access.

This model costs more than a basic non-condensing heater. The final bill may also include service valves, vent pipe, a condensate drain, gas-line work, a controller, permits, and labor. The higher entry price makes the most sense for a family that uses hot water throughout the day.

Best match: A three- or four-bathroom home, a large family, or a house with a long recirculation loop.

Best Premium Model Without an Internal Pump: Rinnai RX199iN

The Rinnai RX199iN shares much of the RXP model’s core performance. It has an 11.1 GPM maximum rating, a 0.98 UEF rating, Wi-Fi capability, and a burner that reaches 199,000 BTU. The main difference is the lack of a built-in recirculation pump.

That missing pump may sound like a drawback, but it can save money when your home does not need recirculation. A compact house with short pipe runs may deliver hot water quickly enough without one. Some homes also have an existing external pump that the owner wants to keep.

The RX199iN is a better fit than the RXP199iN when strong heating power matters more than instant delivery at a faraway faucet. It is also lighter than many older premium units, which may make wall placement easier for the installer.

Check the Rinnai RX199iN on Amazon.

Best for Recirculation Comfort: Navien NPE-240A2

The Navien NPE-240A2 is one of the strongest choices for a home that values shorter waits at the faucet. It has an internal recirculation pump and a small buffer tank. The buffer tank helps reduce brief temperature swings that can occur when water use stops and starts.

Its flow ratings also tell an honest story about tankless sizing. Navien rates it at 11.2 GPM with a 35°F temperature rise, 8.7 GPM with a 45°F rise, and 5.6 GPM with a 67°F rise. That drop is normal. Every tankless water heater loses flow as the required temperature rise grows.

A home in Florida may feed the heater with relatively warm water. A home in Minnesota may receive water that feels like melted snow. Both homes may set the shower to the same temperature, but the northern unit must add far more heat. That extra work lowers the number of gallons it can heat each minute.

The NPE-240A2 works well for households that often run two showers at the same time. It can also support a dishwasher or faucet beside them under moderate conditions. A plumber should still calculate the winter inlet temperature and peak household demand before purchase.

Best match: A family that dislikes long waits for hot water and wants a built-in pump rather than a separate recirculation package.

Best Combination Unit: Noritz NRCB199DV

The Noritz NRCB199DV handles domestic hot water and hydronic space heating inside one cabinet. It can feed faucets while also serving compatible radiators, baseboard heat, or radiant floor loops. This makes it different from a standard tankless water heater.

Its domestic hot-water flow range reaches 11.1 GPM under favorable conditions. The burner can reach 199,900 BTU for water heating. The unit is made for indoor or outdoor wall mounting, though the full installation depends on climate and local code.

A combination unit can free floor space and reduce the number of large appliances in a mechanical room. Still, it requires careful sizing. The installer must account for bathroom demand and the heating load of the house. A model that looks powerful on paper may still struggle if both needs are guessed rather than measured.

The NRCB199DV is not the right purchase for someone who only needs a basic shower heater. It is meant for homes where domestic hot water and hydronic heat belong in the same package.

Best Electric Tankless Water Heater: Stiebel Eltron Tempra 36 Plus

The Stiebel Eltron Tempra 36 Plus is my preferred electric model for whole-house use. Its best feature is automatic flow control. When hot-water demand rises beyond the heater’s capacity, the unit can reduce water flow to protect the selected outlet temperature.

That response is better than a heater that lets the shower turn lukewarm without warning. The Tempra 36 Plus acts like a careful gatekeeper. It may slow the stream, but it tries to keep the water hot.

The 36 kW rating requires a large electrical supply. Many homes need three separate double-pole breakers for a heater in this class. The main service panel must also have enough capacity for the new load. An older 100-amp panel will rarely be a happy partner for a large electric tankless unit.

Electric tankless heaters have no gas burner, combustion vent, or flue. That can reduce installation work in the right house. Yet panel upgrades and heavy copper wiring can erase those savings. Ask an electrician to inspect the service before ordering the heater.

The Tempra 36 Plus is strongest in warm or moderate regions. In a cold region, it may serve one shower and a faucet rather than several heavy fixtures at once.

Check the Stiebel Eltron Tempra 36 Plus on Amazon.

Best Lower-Cost Electric Pick: Rheem RETEX-36

The Rheem RETEX-36 is a 36 kW electric model with digital temperature control. Rheem lists a flow rate of up to 8.8 GPM, though that figure represents favorable inlet conditions. A cold winter inlet will reduce the usable flow by a wide margin.

This model suits buyers who want whole-house electric water heating without paying the premium attached to the Stiebel Eltron Tempra Plus. It has a copper heat exchanger, bottom water connections, and temperature adjustment in one-degree steps.

The same electrical warning still applies. A 36 kW heater draws a great deal of power. The panel, breakers, wire, and service entrance must support it. Never treat this model like a small appliance that can be placed on an open household circuit.

Check the Rheem RETEX-36 on Amazon.

Best Electric Pick for Warm Climates: EcoSmart ECO 36

The EcoSmart ECO 36 is another 36 kW option. It has a small wall-mounted cabinet and four 9 kW heating sections. It may work well in a warm region where incoming water already starts at a moderate temperature.

Its low purchase price can be tempting, but the electrical demand is heavy. EcoSmart calls for four 40-amp double-pole breakers and a main electrical service that can support the total load. That requirement can turn an inexpensive heater into a costly project when the home needs a new panel.

The ECO 36 makes the most sense for new construction, a home with spare electrical capacity, or a warm-climate property with modest simultaneous demand. It is a weaker choice for a cold-climate family that expects three showers at once.

Check the EcoSmart ECO 36 on Amazon.

Gas or Electric: Which Type Is Better?

A gas tankless water heater is usually the better whole-house choice for a family with two or more bathrooms. Gas burners can add heat to fast-moving water at a rate that standard residential electrical service often cannot match.

Gas installation can still become expensive. The home may need a larger gas line, new vent pipe, a condensate drain, fresh-air access, or an outdoor mounting location. A condensing model also creates acidic condensate that must drain through approved materials.

Electric tankless heaters are smaller and need no combustion vent. They work well for a sink, a small apartment, a summer cabin, or a warm-region home with light demand. Their weak point is electrical load. Large units can consume most of the capacity of an older service panel.

Do not choose by fuel price alone. Compare the full installed cost, expected household flow, maintenance needs, and local utility rates.

How Many GPM Do You Need?

Start with the fixtures that may run at the same time. A modern shower may use about 1.5 to 2.5 GPM. A bathroom faucet may use around 0.5 to 1.5 GPM. A kitchen faucet can draw near 1.5 to 2.2 GPM. Appliance demand changes by model and cycle.

A home that may run two 2.0 GPM showers and a 1.5 GPM kitchen faucet needs about 5.5 GPM at the target temperature. That does not mean any heater with “5.5 GPM” printed on the box will work. You need 5.5 GPM at your required temperature rise.

Suppose the winter inlet water is 45°F and the desired outlet is 120°F. The heater must create a 75°F rise. A unit rated at 11 GPM under warm test conditions may deliver close to half that amount under this colder load.

This is the sizing mistake that causes most disappointment. Maximum GPM is the speedometer number. Temperature-rise performance tells you how the car handles a steep hill.

Why Recirculation Matters

A tankless heater does not place hot water beside every faucet. Water still has to travel through the pipes. A distant bathroom can face a long delay even when the heater produces hot water at once.

A recirculation pump moves warm water through a return loop or a compatible crossover valve. The result is faster delivery at the fixture. Some pumps run on a schedule. Others respond to a button, motion sensor, app command, or learned household pattern.

Constant recirculation can waste fuel because the pipes lose heat. Timed or demand-based operation is usually the better choice. Pipe insulation also helps the water hold its heat during the trip.

Installation Costs People Often Miss

The heater is only one part of the bill. A gas installation may need isolation valves, vent parts, a gas-line upgrade, wall brackets, a condensate neutralizer, drain tubing, pipe changes, an electrical outlet, and permit fees.

An electric installation may need thick wire, several breakers, panel work, a service upgrade, new shutoff valves, and fresh plumbing connections. The electric unit may look cheaper in the cart, but the wall behind it can hide a much larger expense.

Get a written quote before buying the unit. Some contractors will not install equipment supplied by the homeowner. Others may offer limited labor coverage on customer-supplied heaters. Ask about this before the box reaches your door.

Maintenance and Hard Water

Minerals can collect inside the heat exchanger. Hard water leaves scale like chalk inside a narrow pipe. As the layer grows, heat transfer drops and water passages become tighter.

Many homes need a periodic flush with an approved descaling liquid. The schedule depends on water hardness, household use, and the maker’s directions. Isolation valves make this job far easier.

A sediment filter can protect the inlet from debris. A water softener may also help in areas with severe hardness. Keep the air intake clear, inspect vent parts, and clean inlet screens as directed.

Skipping care can shorten service life and cause temperature swings, noise, ignition trouble, or reduced flow. A tankless unit is compact, but it is not maintenance-free.

Common Tankless Water Heater Mistakes

The first mistake is buying by maximum GPM alone. The second is ignoring winter groundwater temperature. The third is assuming “endless hot water” means unlimited flow. A tankless heater can run for a long time, but it can only heat a set amount of water each minute.

Another mistake is choosing electric before checking the panel. Buyers sometimes order a 36 kW unit and later discover that the house cannot power it without a major service upgrade.

Gas buyers may overlook venting and fuel supply. A large burner needs enough gas under full load. A narrow or long gas line may not deliver it. Poor sizing can cause ignition faults and weak performance.

Do not set the temperature higher than needed in an attempt to gain more hot water. That raises burn risk and may increase mineral buildup. Most homes are comfortable near 120°F, though personal needs and local rules differ.

Which Tankless Water Heater Should You Buy?

Choose the Rinnai RXP199iN when you want the best tankless water heater for a large family, high peak demand, strong fuel economy, and built-in recirculation.

Choose the Rinnai RX199iN when you want nearly the same heating performance but do not need an internal pump.

Choose the Navien NPE-240A2 when short faucet waits and stable delivery matter most. Its pump and buffer tank make it a strong comfort-first choice.

Choose the Noritz NRCB199DV when the same appliance must handle domestic water and hydronic home heat.

Choose the Stiebel Eltron Tempra 36 Plus when gas is not available and your electrical service can support a large whole-house heater. Its automatic flow control gives it an edge over cheaper electric models.

Choose the Rheem RETEX-36 or EcoSmart ECO 36 for a lower purchase price in a warm climate or a home with modest peak demand.

The best purchase is not always the unit with the largest number on the label. It is the heater that matches your coldest inlet water, busiest hour, available fuel, pipe layout, and installation budget. Get those five pieces right, and a tankless water heater can serve as a steady furnace for every shower, sink, and wash cycle in the house.