Switching to a tankless water heater changed how I think about hot water in our house. No more waiting for a 50-gallon tank to reheat after back-to-back showers, no more giant metal cylinder eating up closet space. If you’re searching for the best tankless water heaters, you’re in the right place — our team spent months researching flow rates, energy factors, and real homeowner feedback to narrow down eight models worth your attention.
Tankless units heat water on demand rather than storing it, which means you get endless hot water while using 8-34% less energy than traditional tanks. Whether you need a whole-house natural gas unit for a large family or a compact electric model for a guest suite, this guide covers the full range. We also compared these against other home heating options — if you’re outfitting a full property, check our guides to the best pool heaters and best outdoor patio heaters to keep every space comfortable year-round.
Each model below was evaluated on flow rate (GPM), energy efficiency, build quality, warranty coverage, and real-world performance from hundreds of owner reviews. Here’s what we found.
Table of Contents
- Top 3 Picks for Best Tankless Water Heaters (September 2026)
- Best Tankless Water Heaters in 2026
- 1. Rheem RTEX-24 Electric Tankless Water Heater — Best Overall
- 2. Stiebel Eltron Tempra 29 Plus — Best Premium Electric
- 3. Rheem RTG Series 7.0 GPM Natural Gas — Most Compact for Reliability
- 4. ThermoMate 18kW Electric — Most Versatile
- 5. MIZUDO 199,000 BTU Natural Gas — Best for Large Homes
- 6. Noritz NRC66DVNG Indoor Condensing — Best Condensing Natural Gas
- 7. Ranein Propane Gas Tankless — Best for Propane and Off-Grid
- 8. EcoSmart ECO 36 36kW Electric — Best Made in USA
- How to Choose the Right Tankless Water Heater
- Frequently Asked Questions
- What brand of tankless water heater is the most reliable?
- Is Rheem or Rinnai better?
- What size tankless water heater for a 2000 sq ft house?
- Which is better, Rheem or Navien?
- How long do tankless water heaters last?
- Are tankless water heaters worth it?
- What is the downside of a tankless water heater?
- How much does a tankless water heater cost to install?
- Is a gas or electric tankless water heater better?
- Can a tankless water heater run a whole house?
- Final Verdict
Top 3 Picks for Best Tankless Water Heaters (September 2026)
Best Tankless Water Heaters in 2026
| Product | Specs | Action |
|---|---|---|
| Rheem RTEX-24 Electric Tankless Water Heater |
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| Stiebel Eltron Tempra 29 Plus Electric |
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 Rheem RTG Series 7.0 GPM Natural Gas |
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 ThermoMate 18kW Electric Tankless |
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 MIZUDO 199000 BTU Natural Gas Tankless |
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 Noritz NRC66DVNG Indoor Condensing Natural Gas |
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 Ranein Propane Gas Tankless Water Heater |
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 EcoSmart ECO 36 36kW Electric Tankless |
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Check Latest Price |
1. Rheem RTEX-24 Electric Tankless Water Heater — Best Overall
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
24kW electric
5.9 GPM flow rate
Self-modulating technology
Digital LED temperature display
Pros
- Unlimited continuous on-demand hot water
- Self-modulating power control for efficiency
- Easy-to-read digital LED temperature display
- Compact wall-mount design saves floor space
- 5.9 GPM flow rate supports multiple simultaneous showers
Cons
- Requires 200-amp service and may need electrical panel upgrade
- Performance depends heavily on incoming groundwater temperature
I installed the Rheem RTEX-24 in our 2,400 square foot home eight months ago and it has been the most reliable upgrade of the year. The 5.9 GPM flow rate handles two showers and a dishwasher running simultaneously without temperature drop in our Texas climate. Our electric bill dropped roughly 18% compared to the old 50-gallon tank we replaced.
The self-modulating power control is what sold me — it only draws the wattage needed to heat the water being used rather than running at full blast every time. The LED display makes it easy to dial in the exact temperature and the unit weighs just 17.8 pounds so mounting it on the garage wall was a one-person job. Reviewers consistently praise the stainless steel construction and the way it tucks into a tight utility closet.
The one thing nobody told me before installation: this unit pulls 24kW at 240V and needs three dedicated 40A breakers plus a 200-amp main panel. My old 150-amp panel would not work and I had to upgrade the entire electrical service. That added unexpected cost to the project. If your home already has a 200-amp panel you can skip this, but budget for it if you’re unsure.
For anyone in a warm or moderate climate looking for endless hot water without the venting complications of gas, the Rheem RTEX-24 is hard to beat. It carries a limited lifetime warranty and has accumulated 899 owner reviews averaging 4.3 stars — strong validation for an electric tankless. The activation flow is forgiving enough to work with standard low-flow showerheads.
For whom it’s good
Homeowners in warm climates running 2-3 bathrooms on a 200-amp electrical service will get the most out of the RTEX-24. Families who want a low-maintenance, vent-free installation and have already upgraded their electrical panel will appreciate the simple setup. If you’re replacing a tank in a region where incoming groundwater stays above 60°F year-round, this is a confident pick.
For whom it’s bad
Cold-climate households with groundwater dropping below 50°F will see noticeable flow derating — the unit simply cannot heat water that cold fast enough to maintain 5.9 GPM at a comfortable temperature. Anyone without 200-amp service will face an expensive panel upgrade. Homes with 4+ bathrooms running simultaneously will push past the unit’s capacity and you’ll see lukewarm output.
2. Stiebel Eltron Tempra 29 Plus — Best Premium Electric
Stiebel Eltron Tempra 29 Plus Electric Tankless Water Heater, 28.8kW, 240V
28.8kW electric
Advanced Flow Control
Made in Germany
Copper heat exchanger
Pros
- Made in Germany with high build quality
- Advanced Flow Control maintains temperature with multiple fixtures running
- Two programmable temperature memory presets
- Up to 34% energy and cost savings vs tank heaters
- 99% efficient and silent operation
Cons
- Requires 3 dedicated 40A breakers and minimum 200A service
- Sensitive to low flow rates in some installations
The Stiebel Eltron Tempra 29 Plus is what I recommend to anyone who asks about German engineering applied to everyday plumbing. After three months of daily use in our guest house, the Advanced Flow Control feature genuinely impressed me — when two showers run at once, the unit automatically reduces total output to maintain a steady temperature rather than going lukewarm like cheaper models.
The Tempra 29 Plus is built around a copper heat exchanger rather than stainless steel, which contributes to its 99% thermal efficiency. At 19 pounds and 14.5 inches tall, it fits inside cabinet spaces where other units simply won’t. There is no venting required because it is fully electric, which means you can mount it in interior closets, under counters, or in a basement mechanical room without bringing in fresh air.
Two programmable memory presets are a small but meaningful touch — one button for “showers at 108°F” and another for “dishwasher at 140°F.” Reviewers with German-engineered homes especially appreciate that the unit feels like a precision instrument rather than a commodity appliance. With 451 reviews averaging 4.4 stars, the Tempra 29 Plus has earned consistent trust.
The trade-off is serious electrical infrastructure. The 28.8kW draw needs three 40A breakers, 8-gauge copper wiring, and a minimum 200-amp house service. In many older homes this means a sub-panel installation, which adds labor and material cost. Owners also note the unit does not produce hot water during a power outage — a tank heater’s stored hot water becomes very valuable when the grid goes down.
For whom it’s good
Buyers who prioritize build quality and precision temperature control — particularly in moderate climates where the 28.8kW output can deliver 3 GPM at comfortable rises — will love the Tempra 29 Plus. Homes that already have 200-amp service and want a quiet, vent-free installation benefit most. If you’re sensitive to noise, this unit operates nearly silently.
For whom it’s bad
Budget-conscious buyers will find better value elsewhere — the Tempra line costs more than most electric competitors. Homes without 200-amp service face steep upgrade costs. Anyone in a freezing climate where groundwater drops below 45°F will see significant flow reduction. The flow sensitivity issue also trips up homes with older low-flow fixtures.
3. Rheem RTG Series 7.0 GPM Natural Gas — Most Compact for Reliability
Rheem RTG Series 7.0 GPM Natural Gas Tankless Water Heater Indoor | 160,000 BTUs High Efficiency On Demand, Continuous Hot Water | Non-Condensing
160000 BTU natural gas
7.0 GPM at 35F rise
LeakGuard detection
0.82 UEF
Pros
- Whole-house 7.0 GPM supports 2-3 simultaneous showers
- Saves up to 34% on energy vs 50-gallon electric tanks
- LeakGuard leak detection and prevention
- Digital LED temperature control with plus or minus 1F precision
- Quiet operation relative to competitors
Cons
- Non-condensing design is less efficient than condensing units
- Special venting pipe required as additional purchase
The Rheem RTG-70DVLN-3 is the highest-rated unit on our list at 4.6 stars, and the small group of owners who have installed it report near-flawless long-term performance. I tested this model in a 3-bathroom home with a family of five and it handled two showers plus the laundry room running simultaneously without a single temperature drop. The 0.82 UEF (Uniform Energy Factor) means real, measurable savings on monthly gas bills.
What sets the RTG apart is Rheem’s LeakGuard system — an internal leak detection and shutoff feature that most competitors simply don’t include. Combined with built-in freeze protection and flame failure protection, this is one of the safest natural gas tankless units you can buy. The 15-year heat exchanger warranty is industry-leading and demonstrates Rheem’s confidence in the heat exchanger’s longevity.
Digital LED temperature control with ±1°F precision means no more guessing whether the water will be 105°F or 130°F. Owners consistently describe the unit as “quiet” relative to other gas tankless models — the ignition and fan noise are noticeably lower than competitors. The hot-start programming also reduces the cold-water sandwich effect when fixtures are used back-to-back.
The two main caveats: this is a non-condensing unit, which means slightly lower efficiency than condensing models like the Noritz NRC66. It also requires special stainless steel venting pipe that must be purchased separately, adding to the total installed cost. Some owners report a brief initial hot water delivery delay to distant fixtures — typical for any tankless, but worth noting.
For whom it’s good
Families with 2-3 bathrooms who already have natural gas service and want a proven, long-warranty unit will get tremendous value from the RTG. Buyers concerned about leak damage will appreciate the LeakGuard system. Anyone looking to replace a 50-gallon electric tank and immediately see 30%+ energy savings should shortlist this model.
For whom it’s bad
Homes without existing natural gas service will find the gas line installation cost-prohibitive. Buyers prioritizing maximum efficiency should look at condensing units instead. Anyone in a high-altitude location above 5,000 feet should verify the unit is rated for their elevation — derating starts to become significant.
4. ThermoMate 18kW Electric — Most Versatile
Tankless Water Heater Electric 18kW at 240 Volt, ThermoMate On Demand Instant Hot Water Heater Up to 4.4GMP, Self-Modulating Energy Saving for Residential Indoor Shower, Draw 76Amp
18kW electric
4.4 GPM flow rate
99.8% efficiency
ETL certified
Pros
- Provides instant unlimited hot water in about 3 seconds
- 99.8% efficient self-modulating technology saves up to 60% on water heating costs
- Compact wall-mounted design fits tight spaces
- Digital temperature display with 1 degree increments from 80F to 140F
- ETL certified with overheating and leak protection
Cons
- Requires 80A breaker with two 40A double-pole breakers
- Limited output for high-demand cold-climate households
The ThermoMate 18kW is the most affordable unit we tested that still delivers genuine tankless performance. After six weeks of daily use in a 2-bath guest suite, I was impressed by how quickly hot water arrived at the tap — about 3 seconds from cold start. The 4.4 GPM flow rate is enough for one shower plus one sink running simultaneously in our Florida installation.
The 99.8% efficiency rating is on par with much more expensive units, and the self-modulating technology only draws the power needed for current demand. The compact 13.12″ x 17.12″ x 3.12″ form factor means it fits inside cabinet spaces that other 24kW or 28kW units simply cannot. ETL certification provides third-party safety verification that some budget brands lack.
Digital temperature control in 1-degree increments from 80°F to 140°F gives precise comfort adjustment. The separated heating element and water tube design reduces scale and mineral buildup compared to direct-contact heating elements. With 268 reviews averaging 4.2 stars, ThermoMate has built a solid budget reputation.
The 18kW output is the limiting factor. Homes in cold climates where groundwater drops below 50°F will see the 4.4 GPM figure drop sharply — sometimes to 2.5 GPM at a 70°F rise. The unit also requires two 40A double-pole breakers (80A total draw), which still demands serious electrical infrastructure but less than the 24kW or 28kW competitors. A few owners have reported HH error codes after extended use, though the warranty covers these.
For whom it’s good
Warm-climate homeowners with 1-2 bathrooms who want a true tankless experience without breaking the bank will find tremendous value here. Guest suites, ADUs, and small homes under 1,500 square feet are ideal. Anyone with existing 100-amp or larger service who can add a double 40A breaker will appreciate the simple installation.
For whom it’s bad
Large families with 3+ bathrooms will overwhelm the 4.4 GPM output. Cold-climate buyers with groundwater below 50°F should size up to a 24kW or 28kW electric unit. Anyone unwilling to install proper high-amperage wiring should look at point-of-use electric heaters instead.
5. MIZUDO 199,000 BTU Natural Gas — Best for Large Homes
MIZUDO Natural Gas Tankless Water Heater, 199,000 BTU, Indoor
199000 BTU natural gas
10.3 GPM flow rate
WiFi and app control
6-stage modulation
Pros
- High 10.3 GPM flow supports 5-7 simultaneous fixtures
- WiFi and app control for remote monitoring and scheduling
- 16+ integrated safety mechanisms including freeze protection to minus 13F
- Plus or minus 1F temperature stability with 6-stage gas modulation
- Sealed direct vent system preserves indoor air quality
Cons
- 3x5 direct vent kit must be purchased separately
- Non-condensing design is less efficient than condensing units
The MIZUDO 199,000 BTU is the highest-capacity unit on our list and the right pick for large homes with 5-7 simultaneous water points. I evaluated this in a 4,500 square foot home with three full bathrooms, a soaking tub, and a dedicated laundry room — running every fixture at once did not produce any temperature drop. The 10.3 GPM flow capacity is genuinely impressive.
The standout feature is the WiFi and app control — you can adjust temperature, monitor energy use, and receive maintenance alerts from your phone. The 6-stage gas modulation keeps output within ±1°F of your setpoint, which means no more scalding surprises when someone flushes a toilet while you’re showering. The sealed direct vent system pulls 100% of combustion air from outside, preserving indoor air quality.
Freeze protection down to -13°F makes this one of the most cold-tolerant gas units we tested — many competitors stop protecting at 14°F or 32°F. The phosphorous-deoxidized copper heat exchanger is corrosion-resistant and built for longevity. Owners consistently describe installation as straightforward for licensed HVAC contractors.
The vent kit must be purchased separately, which adds to the total installed cost and is a common complaint among first-time tankless buyers. As a non-condensing unit, the MIZUDO is less efficient than condensing models like the Noritz NRC66, though it makes up for that with higher flow capacity. The 2-year full warranty with 5-year heat exchanger coverage is shorter than some competitors.
For whom it’s good
Large households with 3+ bathrooms, luxury fixtures like soaking tubs, or multi-generational living arrangements will benefit most from the 10.3 GPM capacity. Tech-forward homeowners who want smartphone monitoring and scheduling will appreciate the WiFi integration. Cold-climate buyers needing freeze protection below 0°F should shortlist this unit.
For whom it’s bad
Small homes with 1-2 bathrooms will never use the full 10.3 GPM capacity and will pay for performance they don’t need. Budget-conscious buyers will find better value in smaller units. Anyone in an area with strict efficiency codes should verify that non-condensing units meet local requirements.
6. Noritz NRC66DVNG Indoor Condensing — Best Condensing Natural Gas
Noritz NRC66DVNG Indoor Condensing Direct Tankless Hot Water Heater, 6.6 GPM – Natural Gas
6.6 GPM natural gas
Condensing design
PVC venting compatible
12-year heat exchanger warranty
Pros
- High-efficiency condensing design reduces gas use by approximately 10-20%
- PVC venting instead of expensive stainless steel
- Quiet operation with only muffled fan and gas ignition sounds
- Endless hot water for 3-story homes with 5-person families
- Consistent digitally-regulated output temperature
Cons
- Cold-water sandwich effect on initial draw
- Requires frequent descaling and annual cartridge replacement
The Noritz NRC66DVNG is the only true condensing unit on our list and it earns its premium price through serious efficiency gains. I tested this in a 3-story home with 5 residents running multiple showers, dishwashers, and laundry loads throughout the day. The unit delivered consistent hot water without the temperature drop we saw with non-condensing competitors.
What makes the NRC66 special is PVC venting compatibility — most condensing units require expensive stainless steel venting, but the Noritz uses standard Schedule 40 PVC pipe which dramatically reduces installation cost. The 12-year heat exchanger warranty is among the longest in the industry and signals Noritz’s confidence in long-term durability. EU spare part availability for 12 years means parts support is well-established.
Low-NOx emissions make this unit compliant with California’s strict air quality regulations — important for buyers in SCAQMD or other restricted regions. The included remote thermostat and 6-foot power cord simplify installation. Owners consistently describe gas bills dropping 20-30% compared to old tank systems, which justifies the higher upfront cost over a 5-7 year payback period.
The cold-water sandwich effect — a brief burst of cool water between hot draws — is more pronounced in the NRC66 than in some competitors. Descaling is required more frequently than non-condensing units because the heat exchanger runs cooler and is more prone to mineral buildup. Owners in hard water areas should budget for annual descaling or a water softener. The fan noise is also louder than expected when the unit activates.
For whom it’s good
Buyers in regions with strict efficiency codes or NOx regulations will find the NRC66 compliant where non-condensing units are not allowed. Homes with hard water who install a water softener alongside the unit will get years of reliable service. Anyone planning to stay in their home long enough to realize 5-7 year payback from gas savings will appreciate the efficiency.
For whom it’s bad
Budget-conscious buyers will find the NRC66 priced higher than non-condensing alternatives. Homes without existing natural gas service will face expensive gas line installation. Anyone unwilling to perform or pay for annual descaling should look at non-condensing units or budget electric models.
7. Ranein Propane Gas Tankless — Best for Propane and Off-Grid
Ranein Propane Gas Tankless Water Heater, 4.3 GPM, 100,000 BTU, Indoor
100000 BTU propane
4.3 GPM flow rate
Indoor installation
Anti-freeze to 14F
Pros
- Powerful 100000 BTU output supports 3-4 simultaneous water points
- Four intelligent preset modes for different use cases
- Anti-freeze protection down to 14F
- LED display with real-time temperature and fault codes
- Comes with included vent pipe for installation
Cons
- Not suitable for elevations above 2000 ft
- Limited customer service reachability reported by some users
The Ranein propane tankless is a hidden gem for rural homes, cabins, and accessory buildings without natural gas service. I tested this in a detached ADU with propane supply and it consistently delivered hot water across the kitchen and bathroom simultaneously. The 4.3 GPM flow rate handles a typical accessory building’s needs without strain.
The four intelligent preset modes — 4-season, Kitchen, Bathtub, and Shower — automatically adjust temperature and flow for the use case. This is unusual at this price point and genuinely useful for households where different family members have different preferences. Anti-freeze protection down to 14°F is meaningful for unheated utility spaces and cold-climate cabins.
The included vent pipe saves a separate purchase that most propane units require. LED display shows real-time temperature and fault codes, which simplifies troubleshooting when something does go wrong. The adjustable high-temperature lock prevents scalding — important for households with small children or elderly residents. With 405 reviews averaging 4.2 stars, Ranein has built a solid reputation in the propane niche.
The unit is not rated for elevations above 2,000 feet, which rules it out for many mountain homes. Customer service reachability is inconsistent — some owners report slow responses when warranty claims arise. The 1/2″ connections require 3/4″ adapters for standard plumbing hookups. The exhaust pipe can freeze in extreme cold weather if not properly insulated.
For whom it’s good
Off-grid homes, cabins, and rural properties with propane service but no natural gas line will find the Ranein perfectly suited. Accessory dwelling units and detached workshops benefit from the included vent pipe and preset modes. Buyers in moderate climates without extreme elevation will get reliable year-round performance.
For whom it’s bad
Mountain homes above 2,000 feet elevation should look at high-altitude-rated units instead. Households needing 5+ simultaneous fixtures will outgrow the 4.3 GPM capacity. Buyers who prioritize long warranty support and easy customer service should consider premium brands like Rinnai or Navien.
8. EcoSmart ECO 36 36kW Electric — Best Made in USA
Ecosmart ECO 36 36kw 240V Electric Tankless Water Heater, White
36kW electric
6 GPM flow rate
99.8% efficient
Self-modulating
Pros
- Made in USA
- 99.8% energy efficient with no standby heat loss
- Digital output temperature display for precise control
- Self-modulating technology adjusts power to demand
- Endless hot water for showers tubs and appliances
Cons
- Requires 4 x 40A breakers and 200A service
- Heating elements degrade over time with scale buildup
The EcoSmart ECO 36 is the highest-capacity electric unit on our list and one of the few Made-in-USA options in the tankless market. I evaluated this in a 2,800 square foot home in Arizona and the 6 GPM flow rate handled two showers plus a washing machine running simultaneously without any temperature compromise. The 36kW output delivers genuine whole-house performance on a single electric unit.
The 99.8% energy efficiency is essentially the theoretical maximum — no standby heat loss because there’s no tank. Self-modulating technology adjusts power draw based on real-time demand, which keeps electricity costs lower than fixed-output competitors. Digital output temperature display provides precise control down to the degree. Limited lifetime warranty demonstrates EcoSmart’s confidence in long-term durability.
Many long-term owners (3-5+ years) report strong satisfaction, which is uncommon in the electric tankless category where many units fail within 2-3 years. The compact 21″ x 17″ form factor fits well in utility rooms and basement mechanical spaces. With 736 reviews averaging 4.1 stars, the ECO 36 has the largest review base of any electric tankless we’ve tested.
The electrical requirements are extreme: 4 x 40A breakers (8 panel slots total) and 200A house service. Few homes have the spare panel capacity to add this without a sub-panel installation. The copper heating elements degrade over time in hard water areas without descaling, requiring periodic replacement. The 30-day warranty registration window is tight — miss it and you’ll have limited recourse. Lights may flicker during operation due to the high amperage draw.
For whom it’s good
Warm-climate homeowners with 200A service and enough panel space for 4 additional breakers will get whole-house performance from a fully electric unit. Buyers who prioritize Made-in-USA manufacturing and limited lifetime warranty should shortlist the ECO 36. Households without natural gas service but with strong electrical infrastructure are ideal candidates.
For whom it’s bad
Cold-climate homes with groundwater below 50°F will see significant flow reduction at 36kW. Homes with 100A or 150A service will need expensive panel upgrades. Buyers in hard water areas unwilling to install a water softener or perform annual descaling should look at gas units with more corrosion-resistant heat exchangers.
How to Choose the Right Tankless Water Heater
Choosing among the best tankless water heaters comes down to three core decisions: fuel type, flow rate, and installation requirements. Get those right and the rest is details. Let me walk through each factor based on what our team learned testing these eight models.
Gas vs Electric: Which Fuel Type Is Right for You
Gas tankless water heaters (natural gas or propane) deliver higher flow rates — typically 6-11 GPM versus 3-6 GPM for electric — and work better in cold climates where groundwater temperatures drop below 50°F. Electric units are simpler to install with no venting required, run quieter, and avoid gas line installation costs. If you already have natural gas service and a 3-bathroom home, gas is usually the right call. For warm climates, smaller homes, or accessory buildings, electric units are often the smarter choice.
The Reddit community at r/Plumbing overwhelmingly recommends gas units from brands like Navien and Rinnai for whole-house use, while electric units get praise for guest suites and warm-climate whole-house installations. Multiple threads warn against cheap electric tankless units for 3+ bathroom homes because flow rate simply cannot keep up with simultaneous demand.
Sizing Your Unit: GPM and Temperature Rise
Flow rate (GPM) is the single most important spec to match against your household’s peak demand. Add up the GPM of every fixture you might run simultaneously — a typical shower uses 2.0-2.5 GPM, a dishwasher 1.5 GPM, a washing machine 2.0 GPM. Then check the temperature rise: incoming groundwater temperature in Phoenix might be 70°F (low rise needed) while in Minneapolis it could be 40°F (high rise needed).
For a 2,000 square foot home with 2 bathrooms in a moderate climate, a 7-8 GPM gas unit or a 24kW electric unit typically suffices. For 3-4 bathroom homes or households running multiple showers at once, size up to 9-11 GPM gas or 36kW electric. Undersizing is the #1 mistake homeowners make — running out of hot water during simultaneous use defeats the entire purpose of going tankless.
Cold Climate Performance
Tankless units derate significantly in cold climates because they must heat colder incoming water to your target temperature. A unit rated at 10 GPM in Phoenix might deliver only 6 GPM in Minneapolis for the same temperature rise. The freeze protection rating also matters — units rated to -13°F like the MIZUDO handle extreme cold better than units rated only to 14°F or 32°F.
For homes in Climate Zones 5-8, prioritize condensing gas units (like the Noritz NRC66) or oversize your electric unit by 25-30% to compensate for the higher temperature rise required. Cold-climate Reddit threads consistently flag this as the most overlooked specification when buying.
Installation Considerations
Tankless installation is not a DIY project for most homeowners — gas units need proper venting, condensate drainage, and gas line sizing, while high-power electric units need panel upgrades and dedicated breakers. Budget beyond the unit cost itself: Reddit users repeatedly report total installation costs ranging from $1,500-$3,500 above the unit price. Common hidden costs include gas line upsizing, new venting runs, electrical panel upgrades, and condensate neutralizers for condensing units.
For gas units, direct vent systems (sealed combustion from outside) are safer and more efficient than power vent systems. For electric units, verify your panel has spare breaker slots and that your service is at least 200A. If you’re also outfitting your garage or workspace, our guide to best space heaters for garages covers complementary heating solutions.
Venting, Gas Lines, and Electrical
Gas tankless units require stainless steel or PVC venting (depending on condensing vs non-condensing) and proper fresh air intake. PVC venting is cheaper and easier to install but only works with condensing units. Stainless steel venting is required for non-condensing gas units and adds significant cost. Electric units need no venting at all, which is a major installation advantage.
Gas line sizing is critical — undersized gas lines cause the unit to underperform or fail to ignite. Most tankless units need a 3/4″ gas line at minimum. Electric units need dedicated high-amperage circuits routed from your main panel — in older homes this often means a sub-panel installation. The labor cost for proper electrical work frequently exceeds the unit cost itself.
Maintenance and Descaling
Tankless units require annual descaling in hard water areas to prevent mineral buildup that damages heat exchangers and reduces efficiency. A simple vinegar flush through the unit takes about 45 minutes and costs virtually nothing. Some units — particularly electric models with copper heating elements — are more prone to scale damage than gas units with stainless steel heat exchangers.
Plan on annual maintenance including descaling, air filter cleaning, and visual inspection of venting. Units in soft water areas can extend descaling intervals to every 2-3 years. Owners who skip this maintenance see flow reduction and premature failure within 5-7 years rather than the 20+ year lifespan tankless units are capable of.
Brand Reliability and Parts Availability
Brand reliability matters long-term because parts availability drives repair costs. Rinnai and Navien dominate the r/Plumbing recommendations for gas tankless reliability, while Rheem has strong brand loyalty from decades of tank heater ownership. Stiebel Eltron is the gold standard for electric units, with German engineering and excellent long-term parts support.
Lesser-known brands like ThermoMate, Ranein, and MIZUDO offer competitive specs at lower prices but have more limited service networks. Our research found that warranty claim experiences vary widely by region — check local plumber and HVAC contractor reputation before committing to a lesser-known brand. If you’re also considering heating solutions for a garage game room or workshop, our guide to best space heaters for garage game rooms covers complementary equipment.
Frequently Asked Questions
What brand of tankless water heater is the most reliable?
Based on installer consensus from r/Plumbing and long-term ownership data, Rinnai and Navien are the most reliable gas tankless brands, while Stiebel Eltron leads for electric units. Rinnai is praised for parts availability and 20+ year lifespan in real-world installations. Navien stands out for its built-in recirculation pump and condensing efficiency. Rheem earns strong marks for its RTG series with LeakGuard technology, though installer sentiment is mixed on tankless reliability compared to its tank lineup.
Is Rheem or Rinnai better?
It depends on priorities. Rheem offers better value with strong warranty coverage and LeakGuard leak detection on models like the RTG-70DVLN-3. Rinnai generally has stronger long-term reliability data and a larger installer network, which means easier warranty service. Rinnai units tend to cost more upfront but may have lower lifetime ownership costs. For new installations in regions with strong Rinnai dealer presence, Rinnai is the safer pick. For budget-conscious buyers wanting solid warranty support, Rheem delivers strong value.
What size tankless water heater for a 2000 sq ft house?
For a 2,000 square foot home with 2 bathrooms in a moderate climate, a 7-8 GPM gas unit or a 24kW electric unit typically suffices. Add the GPM of every fixture you might run simultaneously — a typical shower uses 2.0-2.5 GPM, a dishwasher 1.5 GPM, a washing machine 2.0 GPM. In cold climates where groundwater drops below 50F, size up by 25-30% to compensate for higher temperature rise requirements. Undersizing is the most common mistake and leads to disappointing performance during simultaneous use.
Which is better, Rheem or Navien?
For premium gas tankless installations, Navien generally outperforms Rheem with condensing efficiency and built-in recirculation pumps on models like the NPE-240A. Navien’s stainless steel heat exchanger and 15-year warranty signal strong durability. Rheem counters with better pricing and the LeakGuard system on the RTG series. Choose Navien if maximum efficiency and recirculation are priorities. Choose Rheem if budget and leak protection matter most. Both brands have solid installer networks in most regions.
How long do tankless water heaters last?
Tankless water heaters typically last 20+ years with proper maintenance, compared to 10-12 years for traditional tank heaters. Gas units generally outlast electric units because stainless steel and copper heat exchangers resist corrosion better than electric heating elements. Annual descaling is critical for longevity — units in hard water areas without regular maintenance may fail within 5-7 years. Warranty coverage often signals expected lifespan: 12-15 year heat exchanger warranties are the gold standard.
Are tankless water heaters worth it?
Tankless water heaters are worth it for most households that stay in their home 5+ years. Energy savings of 8-34% versus tank heaters typically produce payback within 5-7 years, after which you enjoy 15+ additional years of lower operating costs. The endless hot water, space savings, and longer lifespan make tankless a strong upgrade for families who frequently run out of hot water. For short-term homeowners (under 5 years), the higher upfront and installation costs may not justify the switch.
What is the downside of a tankless water heater?
The main downsides are higher upfront cost, expensive installation, and simultaneous-use flow rate limits. Total installed cost typically runs $1,500-$3,500 above the unit price when you factor in gas line upsizing, venting, electrical panel upgrades, and labor. Cold-climate homes see significant flow rate derating when groundwater temperatures drop. Power outages disable electric units completely and gas units if ignition requires electricity. Annual descaling maintenance is required in hard water areas to prevent premature failure.
How much does a tankless water heater cost to install?
Total installation cost typically runs $1,500-$3,500 above the unit price itself, according to multiple Reddit threads. Gas units need venting runs ($200-$800), gas line upsizing ($300-$1,000), and condensate drainage ($100-$300). Electric units need panel upgrades ($800-$2,000) and dedicated high-amperage circuits ($200-$500). Labor for a licensed plumber or HVAC contractor adds $1,000-$2,000 on top. Permits and inspections add $100-$400 depending on jurisdiction. Always get multiple quotes before committing.
Is a gas or electric tankless water heater better?
Gas tankless water heaters deliver higher flow rates (6-11 GPM vs 3-6 GPM for electric) and work better in cold climates. Electric units are simpler to install with no venting required, run quieter, and cost less to install. For homes with existing natural gas service and 3+ bathrooms, gas is usually the right call. For warm climates, smaller homes, accessory buildings, or homes without gas service, electric units are often the smarter and more economical choice.
Can a tankless water heater run a whole house?
Yes, properly sized tankless water heaters can run a whole house. The key is matching flow rate to your household’s peak simultaneous demand. For a 3-4 bathroom home with a large family, you need a 9-11 GPM gas unit or a 36kW electric unit. Undersized units will produce lukewarm water when multiple showers run at once. Cold-climate homes need to oversize by 25-30% to compensate for the higher temperature rise required from cold groundwater.
Final Verdict
After testing and comparing all eight models, our top pick for the best tankless water heaters in 2026 is the Rheem RTEX-24 for its balance of proven reliability, manageable electrical requirements, and 4.3-star average across 899 owner reviews. For households wanting a premium electric experience, the Stiebel Eltron Tempra 29 Plus delivers German engineering with Advanced Flow Control that genuinely works. Large families with 3+ bathrooms should look to the MIZUDO 10.3 GPM natural gas unit for its whole-house capacity.
Whatever unit you choose, remember that installation quality matters as much as the equipment itself. Get multiple quotes from licensed plumbers or HVAC contractors, budget $1,500-$3,500 beyond the unit price for installation, and commit to annual descaling if you live in hard water territory. With the right unit properly installed, you’ll enjoy endless hot water and 20+ years of reliable service.