Best Tankless Water Heaters 2021

If 2021 taught homeowners anything, it’s this: hot water is not a “nice-to-have.” It’s a peace treaty between everyone who showers, runs the dishwasher, does laundry, and insists on washing hands like a surgeon. Tankless water heaters (also called on-demand water heaters) became a go-to upgrade because they save space, can reduce energy waste, andwhen sized correctlykeep the hot water coming without the “who used it all?” family meeting.

This guide covers the best tankless water heaters in 2021 (the models and model families that dominated buyer guides, pro installs, and homeowner shortlists), plus sizing, costs, and real-world decision tips. The goal: help you pick a unit that matches your homeso your shower doesn’t turn into an unscheduled cold-plunge challenge.

How Tankless Water Heaters Work (and Why 2021 Buyers Loved Them)

A traditional tank water heater stores hot water and reheats it all day. A tankless unit heats water only when you turn on the tap. No big storage tank, fewer standby losses, and a smaller footprint. In the right household, that can translate into meaningful energy savingsespecially for lower daily hot-water use patterns.

Here’s the catch: tankless is not “infinite hot water for infinite everything.” It’s more like “continuous hot water up to the unit’s flow limit.” If you ask a unit sized for one shower to handle two showers, laundry, and a dishwasher simultaneously, it will respond the way any of us do under pressure: it will try its best… and then somebody will complain.

Quick Picks: Best Tankless Water Heaters (2021 Standouts)

Pick	Fuel	Best For	Why It Made 2021 Shortlists
Navien NPE-240A2	Gas (condensing)	Big households, high demand	High flow + strong efficiency + built-in recirculation options
Rinnai RUR98iN	Gas (condensing)	Fast “endless” hot water, smart features	Strong flow, recirculation capable, Wi-Fi-ready ecosystem
Noritz NRC111DV	Gas (condensing)	High flow with proven reliability	Well-known pro brand, wide distributor support
Rheem RTGH-95DVLN	Gas (condensing)	Solid whole-home value	Mainstream availability + strong feature set
Stiebel Eltron Tempra 36 Plus	Electric	Top-tier electric performance	Precise control + self-modulation; popular premium electric pick
EcoSmart ECO 27	Electric	Warm climates, smaller homes	Compact, affordable electric whole-home (region-dependent)
Rheem RTEX-06T	Electric	Point-of-use (sink, wet bar, remote bath)	Great “hot water where you need it” fix without a full-home retrofit
Takagi T-H3 (DV/condensing family)	Gas	Heavy residential / light commercial vibes	High capacity and pro-grade orientation

How to Choose the Right Tankless Water Heater

Step 1: Calculate Your Peak Hot-Water Demand (GPM)

Flow rate is measured in gallons per minute (GPM). Add up the fixtures you realistically run at the same time. Example “busy morning” scenario:

• Shower: ~2.0 GPM
• Bathroom sink: ~0.5–1.0 GPM
• Dishwasher (fill cycle): ~1.0–1.5 GPM

That puts you roughly in the 3.5–4.5 GPM neighborhood. If your household regularly runs two showers at once, your peak might jump to 5–7+ GPM fast.

Step 2: Know Your Temperature Rise

A tankless heater’s “headline GPM” depends on how much it needs to heat the incoming water. The bigger the temperature rise, the lower the delivered GPM. To estimate temperature rise, subtract incoming groundwater temperature from your desired output temp.

If you don’t know your flow rate, you can measure it at a faucet using a bucket and a timersimple, low-tech, and oddly satisfying.

Step 3: Pick Fuel Type (Gas vs. Electric) Based on Your Home’s Reality

• Gas tankless (natural gas/propane): Usually best for whole-home needs and multi-bath homes. They can deliver higher GPM at larger temperature rises.
• Electric tankless: Can be excellent, but often demands major electrical capacity for true whole-home performance. In many homes, electric shines as a point-of-use solution or in warm climates.

Step 4: Compare Efficiency Using UEF (and Don’t Obsess Over One Number)

In the U.S., efficiency is commonly expressed as UEF (Uniform Energy Factor), which helps compare models using standardized testing. In general, higher UEF means better efficiencybut installation quality, usage patterns, and maintenance can matter just as much in the real world.

Best Tankless Water Heaters 2021: Detailed Reviews

1) Navien NPE-240A2 Best for High Demand Households

If your home has multiple bathrooms and people who treat showers like podcast episodes, the Navien NPE-240A2 was a standout for capacity and features.

• Max flow: up to 11.2 GPM (at lower temperature rise conditions)
• Efficiency: UEF around 0.95
• Why it worked in 2021: a strong blend of high output, efficiency, and modern controls

Best fit: 3–5+ person households, multi-bath homes, or anyone who’s tired of scheduling showers like a conference room.

2) Rinnai RUR98iN Best “Comfort Upgrade” With Recirculation Capability

Rinnai’s condensing line earned a lot of attention because it paired high output with a comfort-first approach. The RUR98iN is known for strong maximum flow and features aimed at reducing wait time (especially when paired with a recirculation setup).

• Max flow: 9.8 GPM
• Efficiency: UEF around 0.92
• Why it worked in 2021: a premium, widely supported brand with smart-home-friendly options

Best fit: homeowners who want the “why is the shower taking so long to get warm?” problem to move out permanently.

3) Noritz NRC111DV Best for Pros, Parts, and Long-Term Support

Noritz has long been a “plumber’s brand,” and in 2021 the NRC111DV hit the sweet spot for many installations: high capacity with a reputation for durability.

• Flow range: up to 11.1 GPM
• Efficiency: UEF around 0.91
• Why it worked in 2021: dependable performance + broad service network

Best fit: households that want a workhorse model and value serviceability as much as features.

4) Rheem RTGH-95DVLN Best Mainstream Whole-Home Value

Rheem’s tankless options were popular partly because they’re easy to find, widely installed, and backed by a big-name ecosystem. The RTGH-95DVLN series offered condensing efficiency and a flow rate that fits many typical family homes.

• Rated flow: ~9.5 GPM
• Efficiency: UEF around 0.93
• Why it worked in 2021: good balance of performance, availability, and brand familiarity

5) Stiebel Eltron Tempra 36 Plus Best Premium Electric Tankless

If you wanted electric tankless performance without the “my water temperature is freestyle jazz” experience, Stiebel Eltron was a top pick. Its Tempra series is known for tight control and self-modulating power.

• Standout trait: precise temperature stability and smart modulation
• Important reality check: whole-home electric tankless can require substantial electrical service
• Why it worked in 2021: one of the most trusted premium electric names

Best fit: homes prepared for the electrical requirements (and homeowners who hate surprises, especially temperature ones).

6) EcoSmart ECO 27 Best Electric Value (Warm Climate Friendly)

The EcoSmart ECO 27 became a common recommendation for buyers who wanted an affordable electric unit and lived where incoming water isn’t glacier-cold. It can deliver a wide range of GPM depending on inlet temperature.

• Typical range: roughly 2.7–6.5 GPM depending on inlet temperature
• Why it worked in 2021: compact, budget-friendly, and widely discussed in consumer guides

Best fit: smaller households, warm climates, or buyers who can accept that performance shifts with seasons and groundwater temps.

7) Rheem RTEX-06T Best Point-of-Use Fix for Remote Sinks

Not every home needs a full whole-house tankless replacement. Sometimes you just need hot water faster at a far-away bathroom sink, wet bar, or office breakroom. That’s where compact point-of-use electric tankless units shine.

• Use case: one faucet (or two low-flow faucets) near the unit
• Why it worked in 2021: relatively straightforward way to eliminate long waits for warm water

8) Takagi T-H3 Family Best for Heavy Use and “Pro-Grade” Installs

Takagi models often appeared in pro-focused conversations because of their capacity and suitability for heavier demand profiles (and even light commercial settings). If you’re building a system that needs to perform under pressure, Takagi was (and remains) a brand buyers cross-shop seriously.

• Why it worked in 2021: high-capacity orientation, strong use-case range
• Best fit: larger households, high-usage homes, and specialty applications

Common 2021 Tankless Buying Mistakes (So You Can Avoid Them)

Mistake #1: Buying Based on “Max GPM” Only

Always interpret flow rate alongside temperature rise. A unit can advertise a big GPM number at a small temperature rise, then deliver much less when it has to raise water temperature significantly.

Mistake #2: Assuming Electric Whole-Home Is “Plug and Play”

Whole-home electric tankless can be fantastic, but it can also require electrical panel upgrades or additional breakers. If your home’s electrical service isn’t ready, the installation cost may become the plot twist.

Mistake #3: Ignoring Water Hardness and Maintenance

Tankless units have heat exchangers with small passages, and mineral scale can reduce performance and shorten lifespan. If you have hard water, plan for periodic descaling (and consider a water softener or treatment).

Costs and Installation: What 2021 Buyers Typically Faced

Tankless units usually cost more upfront than tank heaters, and installation can be more complexespecially for gas models that may need upgraded venting, gas line sizing, or condensate drainage for condensing units.

• Typical installed cost range: roughly $1,300–$3,900 is commonly cited, with many installs clustering around the midrange.
• Replacement estimates: many consumer resources place tankless replacement totals around $1,200–$3,500 depending on scope and site conditions.

The good news: many tankless units are often described as having long service livesfrequently discussed as reaching around up to ~20 years with good maintenanceso the “pain” is often front-loaded.

Bottom Line: The “Best” Tankless Water Heater Is the One Sized for Your Life

In 2021, the top tankless water heaters weren’t just the ones with fancy displaysthey were the ones that fit the household’s peak GPM, handled the needed temperature rise, and matched the home’s fuel and infrastructure. If you want fewer regrets, do the sizing math first, pick the right fuel type, and budget for professional installation.

Real-World Experiences (The Stuff Specs Don’t Warn You About)

Here’s what homeowners and installers commonly describe after living with a tankless setupthe good, the “huh,” and the “why didn’t anyone tell me this?” moments.

1) The “Endless Hot Water” Myth Gets a Reality CheckFast. One of the most repeated experiences is the first weekend after installation: someone tries to run two showers, the dishwasher, and laundry because “we have tankless now.” The water stays warm, surebut flow can drop or temperatures can wobble if the unit is operating at its limit. People eventually learn the new rule: tankless is unlimited time, not unlimited simultaneous demand. The happiest owners are the ones who sized the unit for peak usage instead of average usage. In other words, size it for your family’s most chaotic morning, not your most peaceful Tuesday.

2) Cold Climates Change the Story. Buyers in warmer regions often report that a midrange electric unit feels magicalsteady hot water, compact footprint, lower upfront equipment cost. Meanwhile, cold-climate owners sometimes discover that the same electric model can behave like a “single-shower specialist” once winter groundwater temperatures arrive. That doesn’t mean electric is bad; it means inlet temperature matters. Many homeowners say the turning point was learning to interpret flow charts by temperature rise rather than relying on a single marketing GPM number.

3) Recirculation Is the Comfort Upgrade People Brag About. If you’ve ever waited a full minute for hot water at a far bathroom sink, you know the pain: you can practically hear your water bill sighing. Owners who add a recirculation strategy (where appropriate) often describe a “hotel hot water” feelingfaster warm-up, less waiting, less wasted water. The flip side is that recirculation adds complexity and needs to be designed correctly, but when it’s done well, it becomes the feature people mention first when friends ask, “Was it worth it?”

4) Maintenance Is BoringUntil You Skip It. The most relatable experience is the one nobody wants: after a year or two, hot water seems a little less hot, or flow feels weaker. Then a plumber says one word: “scale.” Owners in hard-water areas often describe descaling as the difference between “tankless is amazing” and “tankless is moody.” The good news is that once you know the routineespecially with isolation valvesit becomes a manageable calendar item, like changing HVAC filters. Not fun, but less dramatic than emergency repairs.

5) Point-of-Use Units Quietly Save the Day. Some homeowners don’t replace their whole system at all. They add a small point-of-use heater near a remote sink or an addition. The experience they describe is simple: the annoying wait disappears. For many, that targeted fix feels more satisfying than an expensive full retrofit, because it solves a specific daily frustration without changing the entire plumbing ecosystem.

If you take one lesson from these experiences, let it be this: the best tankless water heater isn’t the one with the most buzzwords. It’s the one that matches your home’s infrastructure and your household’s “hot water personality.”