Instant Hot Water Heaters: Tankless Options for Real Households

Waiting two minutes for the shower to warm up while cold water goes down the drain is the everyday annoyance that sends people shopping for an instant hot water heater. Tankless units heat water as it flows instead of storing a full tank, which saves space and avoids the standby heat loss of a tank. They also bring real decisions about electric versus gas, flow rate, and whether your electrical panel can handle the load.

This guide covers six tankless water heaters by name, from electric whole-house units to a portable model, then gives the sizing rules that matter most. As of 2026, the most common mistake is buying on brand without checking the gas line, breaker, or flow rate. Details beyond the name are framed as general buying criteria, so always confirm specifications and local code requirements before purchase.

Quick Picks

How to Choose

Size by flow rate and temperature rise

Add the flow of everything you run at once: a shower uses roughly 2 gallons per minute, a kitchen faucet about 1.5, and a dishwasher or washer 1.5 to 2. Then work out the temperature rise by subtracting your incoming water temperature from 120 degrees. In cold climates with 45-degree incoming water, a 75-degree rise cuts the flow a unit can deliver.

Electric or gas

Electric units are simpler to install and need no venting, but whole-home models draw a lot of current and often need heavy-gauge wiring and several double-pole breakers. Gas units deliver higher flow in cold climates but need a gas line sized to match, plus venting and sometimes a condensate drain. A good rule of thumb is to ask an electrician or plumber to check capacity before you order.

Check efficiency and certification

Look for a published uniform energy factor, which for tankless models commonly falls around 0.90 for electric and 0.82 to 0.97 for gas. Higher is better. Confirm a recognized safety listing, and check whether local code requires a permit and a licensed installer, since many areas do and a skipped permit can complicate insurance claims.

Plan for water quality and maintenance

Hard water leaves scale on the heat exchanger and reduces flow over time. Consider a softener or filter and plan on a descaling flush once a year, more often in hard-water areas. Check whether the unit has an inlet screen you can clean, and whether the warranty requires professional installation to remain valid. Record the model and serial numbers when the unit is installed, and keep the receipt and the installer’s invoice together, since warranty claims on tankless heaters usually ask for both.

Our Picks Reviewed

EcoSmart ECO 27 Tankless Electric Water Heater

Electric and tankless are the two facts in the name, plus a model number of 27.

• Pro: an electric unit needs no gas line or venting, which makes placement easier than for a gas model.
• Pro: tankless design frees up the floor space a storage tank would take.
• Con: larger electric tankless units need substantial wiring and breaker capacity, which an older panel may not offer.

Skip it if your panel is already crowded or if you live where incoming water is very cold and demand is high. It suits homes with enough electrical capacity and moderate hot water use. Have an electrician confirm the circuit requirements before purchase, and ask for a written load calculation. Compare that number with your breaker panel’s remaining capacity, and ask whether the heater needs a dedicated circuit, because adding it to a crowded panel may mean a service upgrade that changes the real cost of the project.

Rheem RTEX-13 Electric Tankless Water Heater

Rheem is a well-known water heater brand, and RTEX-13 is the model, listed as electric.

• Pro: a major water heater brand typically has widespread installer familiarity and parts, which helps with service.
• Pro: electric operation avoids the venting and gas piping needed with other fuel types.
• Con: the 13 in the model hints at a smaller unit, so it may struggle with several simultaneous showers.

Skip it if you have a large household with overlapping hot water use, or very cold incoming water. It suits a small home, an apartment, or a point-of-use installation where flow needs are modest. Compare the listed flow at your local temperature rise rather than the best-case number on the box. A point-of-use unit near a single bathroom or kitchen is often a better match than one whole-home unit, because short pipe runs deliver warm water faster and keep the electrical load small.

Stiebel Eltron Tempra 24 Plus Electric Tankless Water Heater

The name gives a brand, a line, a size figure of 24, and the Plus tier.

• Pro: an electric tankless water heater suits homes without gas service and avoids combustion venting.
• Pro: a Plus tier implies a step up in features within the Tempra line, which may be worth checking for temperature control.
• Con: higher-capacity electric models draw heavily, so panel upgrades can add to the installation cost.

Skip it if you are on a tight budget or cannot upgrade wiring. It suits households with a modern electrical panel and moderate to high demand who want a compact unit. Ask the installer to confirm the breaker size, and plan the unit location close to the main bathrooms to shorten wait times. Think about winter as well: a unit installed in an unheated garage or crawl space needs freeze protection, and a power outage will stop an electric model entirely, so keep a plan for hot water during outages.

Rinnai RU199iN Tankless Water Heater

Rinnai is a major tankless brand, and RU199iN is the model number.

• Pro: a tankless-focused brand usually offers a deep line of models and a service network, which matters when installing a whole-home unit.
• Pro: gas-fired tankless units commonly handle higher flow than electric ones in cold climates.
• Con: gas units require a properly sized gas line and venting, and installation is usually a job for a licensed professional.

Skip it if your home has no gas service or if you want a simple do-it-yourself swap. It suits larger households with high hot water demand and an existing gas supply. Verify the model’s fuel type and venting requirements with the installer before ordering, since model suffixes differ. Ask the installer how the existing gas meter and line will handle the new load alongside a furnace and a range, because a line that was fine for a storage tank can be undersized for a high-output tankless unit.

Navien NPE-240A2 Tankless Water Heater

Navien is another dedicated tankless brand, and NPE-240A2 identifies the model.

• Pro: a brand centered on tankless units tends to offer extra options such as recirculation compatibility, which you can confirm in the specification sheet.
• Pro: tankless design avoids the standby heat loss of a tank and saves space in a utility room.
• Con: a whole-home gas-fired model brings venting, gas line, and permit requirements that add to the project.

Skip it if you prefer a simple point-of-use setup or if your home lacks a gas supply. It suits families that want strong output and are willing to plan the installation carefully. Ask about a recirculation loop if your fixtures are far from the unit. Also ask who handles warranty service in your area and whether a yearly flush is required to keep coverage, since those details matter more over ten years than a small difference in purchase cost.

Eccotemp L10 Portable Tankless Water Heater

Portable and L10 signal a compact unit for use away from a standard home plumbing setup.

• Pro: a portable design suits cabins, camps, and outdoor showers where a full installation is impractical.
• Pro: tankless operation means hot water on demand without waiting for a tank to heat.
• Con: portable units are not designed to supply a whole house, and flow is limited compared with permanent installations.

Skip it if you want hot water for a full family home or to replace a standard tank. It suits seasonal use, a garage sink, or a camp setup. Read the ventilation and safety requirements, since combustion-based units must be used outdoors or in well-ventilated areas. Plan how you will supply water and fuel, protect the unit from freezing temperatures, and drain it between trips, because a unit left full in the cold can crack its internal parts.

Which One Fits

• Electric whole-home with a strong panel: EcoSmart ECO 27 or Stiebel Eltron Tempra 24 Plus.
• Small home or apartment: Rheem RTEX-13 Electric Tankless Water Heater.
• Gas-fueled family home: Rinnai RU199iN or Navien NPE-240A2.
• Cabin, camp, or outdoor shower: Eccotemp L10 Portable Tankless Water Heater.

Common Mistakes

1. Sizing by tank size habits instead of flow rate and temperature rise.
2. Ignoring the electrical panel and breaker capacity on electric models.
3. Skipping a permit or a licensed installer where code requires one.
4. Not descaling in hard-water areas, which cuts flow and shortens life.
5. Expecting a portable unit to supply a full household.

FAQ

Is a tankless water heater truly instant?

Hot water still has to travel from the unit to the fixture, so there is a short wait. A recirculation loop or a unit close to the fixture shortens it.

Do tankless heaters save money?

They avoid standby loss, so savings are greatest in homes with low or moderate use. Heavy use or costly electricity reduces the gap.

Can I install one myself?

Electric and gas work often requires a licensed professional and a permit. Check local code before starting.

What about a hot water supply for a workshop or outdoor space?

Portable units fit, though you may also want warmth in the space itself. See home infrared heaters for options.

Does water heater placement affect my carpet cleaning?

Some deep cleaners need hot tap water to mix solution. If that matters, see the Hoover carpet cleaners guide for what to check.