Instant water heaters, also known as tankless or on-demand water heaters, provide hot water only when needed, eliminating the standby energy losses associated with traditional tank heaters. They heat water as it passes through the unit, offering endless hot water, energy efficiency, and space-saving designs. In 2025, advancements in technology have made instant water heaters smarter, more efficient, and suitable for various household sizes. This guide explores the top 6 instant water heaters of 2025, their pros and cons, testing insights, and a detailed buying guide to help you choose the best model for your home.
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Top 6 Instant Water Heaters of 2025
- 1.1 1. Stiebel Eltron Tempra 36 Plus Electric Tankless Water Heater
- 1.2 2. EcoSmart ECO 27 Electric Tankless Water Heater
- 1.3 3. Rheem RTEX-18 Electric Tankless Water Heater
- 1.4 4. Rinnai RU199iN Non-Condensing Natural Gas Tankless Water Heater
- 1.5 5. Bajaj Splendora 3L 3kW Vertical Instant Water Heater
- 1.6 6. ACTIVA Instant 3 Litre Geyser
- 2 Comparison Table of Top 6 Instant Water Heaters
- 3 Testing Insights and Performance
- 4 Buying Guide for Instant Water Heaters
- 5 Frequently Asked Questions (FAQs)
- 6 Conclusion
Top 6 Instant Water Heaters of 2025
1. Stiebel Eltron Tempra 36 Plus Electric Tankless Water Heater
This model stands out for its high efficiency, endless hot water supply, and space-saving design. It delivers a high flow rate and uses self-modulating technology to automatically adjust energy usage based on your needs. The Tempra 36 Plus is ideal for larger homes with multiple fixtures.
- Pros: High efficiency with 99.8% UEF, self-modulating technology for energy savings, compact design, easy installation, 7-year warranty against leaks.
- Cons: High upfront cost, requires 240V and multiple breakers, not ideal for very cold climates where inlet water is below 50¡ãF.
2. EcoSmart ECO 27 Electric Tankless Water Heater
The EcoSmart ECO 27 makes the top of our list for its $437 price tag and 92,128 BTUs of heating capacity at 99% efficiency. It supplies up to 6.5 gallons of hot water per minute using 27kW of electricity, making it powerful enough for a family of four or five.
- Pros: Affordable at $437, 99% efficiency, self-modulating technology, lifetime limited warranty, compact design saves space.
- Cons: Hot water output drops to 2.7 GPM with very cold inlet water, requires 240V and three 40A breakers, some users report inconsistent performance in winter.
Shop EcoSmart ECO 27 on Amazon
3. Rheem RTEX-18 Electric Tankless Water Heater
Rheem has tremendous experience with both gas and electric tankless water heaters. The high-quality RTEX-18 is rated for up to 4.4 GPM and offers advanced self-modulation, helping it achieve an efficiency rating of 99.8 percent. It’s an impressive yet economical choice for modest homes.
- Pros: 99.8% UEF, easy to install, digital temperature display, self-modulating for energy savings, suitable for one or two showers.
- Cons: Limited to 4.4 GPM, requires 240V and two 40A breakers, not ideal for larger households with high demand.
4. Rinnai RU199iN Non-Condensing Natural Gas Tankless Water Heater
Rinnai RE140iN Non-Condensing Natural Gas Tankless Water Heater stands out in its category, making it our top pick for your hot water needs. It’s built with enhanced scale detection to minimize long-term damage and can provide hot water to several appliances at once.
- Pros: 7.5 GPM flow rate, enhanced scale detection, temperature lock feature, 10-year heat exchanger warranty, Energy Star certified.
- Cons: Expensive, complex installation requiring venting, some users report issues with inconsistent flow in cold climates.
5. Bajaj Splendora 3L 3kW Vertical Instant Water Heater
Bajaj Splendora 3L 3kW Vertical Instant Water Heater For Home|Instant Water Geyser For Bathroom & Kitchen|High Grade SS Tank|Copper Heating Element|1-Yr Product 2-Yr Element 5-Yr Tank WarrantyWhite¡¿ is perfect for small households or point-of-use applications like kitchens or bathrooms.
- Pros: Compact 3L design, high-grade stainless steel tank, copper heating element, affordable, 5-year tank warranty.
- Cons: Limited to 3L capacity, not suitable for whole-house use, lacks advanced smart features.
Shop Bajaj Splendora 3L on Amazon
6. ACTIVA Instant 3 Litre Geyser
ACTIVA Instant 3 Litre Geyser 3 KVA Special Anti Rust Coated 0.7 MM SS Tank, Full Abs Body Premium geyser come with 4 Years Warranty (Grey & Black),Wall is another excellent point-of-use option, offering quick heating and a durable anti-rust coated tank.
- Pros: Affordable, 4-year warranty, anti-rust coated SS tank, compact for small spaces, fast heating.
- Cons: Limited to 3L capacity, not for whole-house use, some users report durability issues after extended use.
Shop ACTIVA Instant 3 Litre Geyser on Amazon
Comparison Table of Top 6 Instant Water Heaters
| Model | Fuel Type | Flow Rate (GPM) | UEF | Warranty | Price Range |
|---|---|---|---|---|---|
| Stiebel Eltron Tempra 36 Plus | Electric | 6.0 | 99.8% | 7 years (leaks) | $700-$900 |
| EcoSmart ECO 27 | Electric | 6.5 | 99% | Lifetime limited | $400-$500 |
| Rheem RTEX-18 | Electric | 4.4 | 99.8% | 5 years | $350-$450 |
| Rinnai RU199iN | Natural Gas | 7.5 | 96% | 10 years (heat exchanger) | $1,200-$1,500 |
| Bajaj Splendora 3L | Electric | 0.5-1.0 | Not specified | 5 years (tank) | $100-$150 |
| ACTIVA Instant 3 Litre | Electric | 0.5-1.0 | Not specified | 4 years | $80-$120 |
Testing Insights and Performance
Simulated Testing Scenarios
Consumer Reports recently tested several electric and gas whole-house tankless water heaters from brands such as Bosch, Navien, Noritz, Rheem, Rinnai, Tempra, and Trutankless. They compared the results with those of conventional tanked heaters from Rheem, one gas and one electric, as well as with a Rheem electric heat pump water heater. Following a “heavy use” industry standard test, they compared the performance of gas and electric tankless water heaters with the performance of their conventional tank counterparts. The test used a high draw pattern equal to using 84 gallons of water per day. That’s the daily equivalent of taking several showers, running the dishwasher, washing one load of laundry, and turning the faucet on and off multiple times. The test used an inlet temperature of 58¡ãF for gas models and 74¡ãF for electrics (plus or minus 2¡ãF) and a target outlet temperature of 120¡ãF.
Because the tankless water heaters performed so similarly to each other, they averaged the results of each batch, gas and electric, and compared that score with the performance of the conventional gas and electric storage tanks and the electric heat pump model. As a result, they have no model-level ratings like they do with other major appliances. Using the purchase price, annual energy cost, and an estimated cost of installation, they calculated the payback time for both new and replacement installations. Payback time was longer for a tankless unit that replaced an existing storage tank but more reasonable with new construction.
Real-World Feedback
We found that customers liked this water heater’s easy setup, consistent performance, and energy savings. Those we found that weren’t pleased with their purchase mentioned issues with the warranty not being honored and tech support not being helpful. Others said it didn’t hold up well during wintertime. “I have this unit in a bathroom with a shower, jacuzzi tub, and two hand washing facets. It covers them all. It gets hot in about 8-10 seconds and much hotter (too hot) in about 20, and I don’t have it turned all the way up. I’ve been using it for about a month. I also installed a larger unit for the kids’ rooms and it is also working flawlessly. Good product for the price and an easy install. I highly suggest using flexible water lines!” ¡ª Amazon Customer via Amazon.
Buying Guide for Instant Water Heaters
Key Factors to Consider
- Fuel Type: Gas tankless water heaters are powered by natural gas or propane tanks. They’re more expensive than electric ones, but part of the reason is that the installation process is more complex. Installation requires access to a natural gas line and ventilation. Gas tankless water heaters are more efficient and heat the water faster than their electric counterparts. They can also service several appliances at the same time.
- Flow Rate (GPM): Tankless water heaters get evaluated by their flow rate or gallons per minute. The higher the GPMs, the more hot water you can run. A typical home needs a flow rate of 6 to 12 gallons per minute. A home of two people needs at least 2 to 3 GPM. A home of three to four people should have a flow of 3 to 5 GPM and homes of five or more people should have 6 GPM or more.
- Household Size: Household numbers – The number of people in homes helps to determine tankless water heater sizes. In most cases, if you live alone, you’ll need a smaller heater. For two residents, a 6–8 GPM heater is effective, while a family of four might need an 8–10 GPM heater.
- Energy Efficiency (UEF): Uniform Energy Factor (UEF): This is a measure of efficiency that can be used to compare water heaters of all types. It represents efficiency as a percentage, so the higher the UEF, the more efficient the model is. According to Energy Star, most traditional storage-type water heaters have a UEF of 0.63 to 0.95, meaning that the least efficient ones (typically gas-fueled models) waste nearly 40 percent of the energy they consume in order to supply you with hot water. Tankless models fare better, with UEFs of gas-fueled models ranging from 0.82 to 0.97.
- Installation Requirements: Switching to tankless from a storage tank water heater is no easy swap because it requires a plumbing retrofit and possibly an upgrade to your electric service or gas lines to increase capacity. Considering that 90 percent of hot water heater installations take place during an emergency, that puts you at a disadvantage when you’re negotiating with a prospective plumber or contractor to make the switch on your tight timeline.
Steps to Choose the Right Instant Water Heater
- Determine your household’s hot water demand by calculating peak usage (e.g., simultaneous showers, dishwasher, laundry).
- Check your home’s electrical or gas infrastructure to ensure compatibility with the heater’s requirements.
- Compare UEF ratings to prioritize energy efficiency and long-term savings.
- Consider space constraints; tankless heaters are compact and can be wall-mounted.
- Review warranty terms and customer feedback for reliability and support.
Frequently Asked Questions (FAQs)
What is the difference between tankless and traditional water heaters?
Tankless water heaters heat water on demand, providing endless hot water without a storage tank, while traditional heaters store and continuously heat a fixed volume of water. Tankless models are more energy-efficient but have higher upfront costs.
Can a tankless water heater support a large family?
Yes, models like the Rinnai RU199iN or Stiebel Eltron Tempra 36 Plus with high GPM (7.5 and 6.0, respectively) can handle multiple fixtures simultaneously, making them suitable for families of five or more.
How much can I save with a tankless water heater?
The U.S. Department of Energy estimates that tankless water heaters can provide energy savings of up to 50 percent, potentially saving $100-$200 annually, depending on usage and fuel type.
Are tankless water heaters difficult to install?
Installation can be complex, especially for gas models requiring ventilation or electrical upgrades for high-power electric units. Professional installation is recommended, with costs averaging $1,300-$3,900.
How long do tankless water heaters last?
Tankless water heaters typically last 20 years or more with proper maintenance, compared to 8-12 years for traditional tank heaters.
Conclusion
The top 6 instant water heaters of 2025 offer a range of options for different household needs, from the high-capacity Rinnai RU199iN for large families to the compact Bajaj Splendora for small spaces. By understanding your hot water demand, fuel type preferences, and installation constraints, you can select a model that balances efficiency, performance, and cost. For more information on energy-efficient appliances, visit Energy Star or consult a professional plumber to ensure a seamless installation.