8 Best Tankless Water Heater Reviews| (Amazon’s Choice)

To offset the chill in a drafty room or to give your home’s heating system a little boost, you may need a space heater.

You and your family will enjoy many benefits once you install the best tankless water heater. You don’t need to be afraid that your tankless water heater is going to explode. They don’t need much maintenance to work properly, and there is no need to worry about replacing these water heaters. You don’t have to wait hours and hours to wait for hot water, you just need to open a tap, and you’ll get hot water whenever you need and how much you need. You don’t need to worry about space either because these water heaters can be installed anywhere in the house.

The tankless water heater usually uses zero energy when you are not using a shower or faucet. It supplies hot water whenever you open the shower or faucet. Their popularity is increasing very rapidly. Tankless, or on-demand water heaters, don’t store water in a tank. Instead, they heat water as it passes through the unit, using a heat exchanger to rapidly increase temperature. 

Our Top Best Choice

Check out this quick list of our favorites if you’re in a rush, or continue scrolling to see our full Top 8 list with in-depth reviews and Common FAQs.

They run on electricity, natural gas, or propane. Heating water only when you need it eliminates the standby energy losses you get with a storage tank. They vary in size but average about 2 feet tall and a bit over a foot wide.

Comparison Table of Top rated Tankless Water Heater

We have a list of the eight best tankless water heater to help you choose

EcoSmart ECO 18
Ecosmart Eco 11
Bosch Electric Mini-Tank Water Heater
Rinnai V65IN Tankless Water Heater
Stiebel Eltron Tankless Water Heater
Rinnai V65EN RV65eN
Rheem RTEX-18 18kW
EcoSmart ECO 18 Electric Tankless Water Heater
Ecosmart ECO 11 Electric Tankless Water Heater
Bosch Electric Mini-Tank Water Heater
Rinnai V65IN Tankless Water Heater
Stiebel Eltron Tankless Water Heater
Rinnai V65EN RV65eN
Rheem RTEX-18 18kW 240V Electric Tankless Water Heater
Best Budget Electric
Best seller
Best Mini Tank
Best Medium-Demand Heater
Best Value Natural Gas
Best Premium Electric
Best for Outdoor
Best High-Demand Heater
Max Flow Rate
Max Flow Rate
6.6 Max GPM
3.3 GPM
6.5 GPM
4.0 Max GPM
Up to 6.6 GPM
Up to 4.4 GPM
Suitable House Size?
Suitable House Size?
Small – Large
Suitable Climate?
Suitable Climate?
All temperature
Technology Used
Technology Used
Flow Sensor technology
Flow Sensor technology
Tronic 3000T
Advanced microprocessor technology
self-modulating water flow technology

1. EcoSmart ECO 11 -Electric Tankless Water Heater

It is an excellent choice for those in need of an affordable tankless water heater. The manufacturer of ecosmart tankless water heaters is a trusted name in the industry; this best electric tankless water heater is considered a premium heater. The Eco 11 is lightweight and compact, making it very easy to install the unit just about anywhere; this best small electric tankless water heater is perfect for a point-of-use system or smaller homes. The heater uses advanced technology to provide a constant hot water supply while reducing energy consumption at the same time.

If you are looking for the most reliable tankless water heater, then EcoSmart ECO 11 is one of the best choices for you. EcoSmart ECO 11 is the highest gallons per minute tankless water heater. It also comes with a lifetime warranty; for this, you receive professional installation.

EcoSmart ECO 11

Key Features:

  • Patented Self Modulating Technology and design 
  • saves up to 60-percent
  • lifetime warranty
  • 99.8-percent energy efficient
  • Never run out of hot water

It is one of the best tankless water heaters of all; You’ll never run out of hot water with an ECOSMART tankless water heater.

Easy to Use and Install:

60 amp power supply and a #6 copper gauge wire are required to install this water heater. The unit includes an automatic and resettable thermostat. The initial temperature is set automatically in this unit, making this water heater easy to use compared to other water heaters.

Energy Efficient Water Heater:

By using a tankless water heater, you can save hundreds of dollars per year. According to the manufacturer, this water heater can save up to 60% of energy bills. The EcoSmart Eco 11 is a very energy-efficient water heater because it turns on whenever needed, and it doesn’t have a standby time. The heater will go off whenever the pipe goes off to saves energy.

Lifetime Warranty:

The manufacturer offers a lifetime warranty for this unit used for residential purposes and installed by a professional. The warranty of this unit includes the electronics, element, and heat exchanger on the water heater. You should read the owner’s manual to know more details about the warranty and what it covers.

  • Energy efficient
  • High GPM for an electronic model
  • Easy to install
  • Temperature Control
  • Its technology controls the unit’s energy output for optimal performance
  • It can heat up to 2 gallons of water per minute
  • All of the components are made out of copper or stainless steel for durability.
  • Warranty requires professional installation
  • Expensive
  • Some users experience water dripping from the bottom of the unit

2. Ecosmart ECO 18 Electric Tankless Water Heater

EcoSmart ECO 18 is an 18-kilowatt tankless electric water heater that provides hot water for apartments, townhomes, and other domestic applications. Its capacity to deliver hot water ranges between 1.8 and 4.3 gallons-per-minute, which depends on the inlet water temperature. With this unit of Ecosmart, you will be happier to know that the warm water you expect is available endlessly, consistently, and on-demand, allowing you to reduce your water and energy waste. Ecosmart is the best electric tankless water heater brand.

It is one of the best electric tankless water heaters for medium-sized households. For a low price, it provides an extraordinary real 4.5 GPM flow rate. In northern states, it can provide up to a 2.3 GPM flow rate. And that’s not just naked specs. It can handle that amount of hot water even without losing much water pressure.

 EcoSmart ECO 18

Key Features:

  • Manufactured in China
  • Lifetime warranty for residential use
  • Save up to 60% on your water heating costs with the most advanced
  • Never run out of hot water with an ECOSMART tankless water heater.
  • Save up to 12 cubic feet of storage space.
  • Self-modulating technology 

It heats the water for the best temperature for the tankless water heater. The digital temperature control allows set outlet temperature in increments of 1 degree to be placed anywhere from 80°F to 140°F.


This product is highly durable. It is not only stable, but it is also easy to use, and it’s the best small electric tankless water heater. Copper and stainless components make it more durable. You’ll never run out of hot water with an ECOSMART tankless water heater.

  • This ECOSMART tankless water heater unit got almost 2 thousand positive reviews on Amazon
  • Lifetime warranty
  • It’s very quiet and starts working slowly
  • It has a self-modulating system to adjusts heat to the current demand. It will never heat the water more than it is needed
  • It comes with a remote to give you control overflow temperature
  • It can cause some trouble If there is not enough circuit load capacity (200+ amps)
  • Warranty void if the unit is not installed by professionals, which sometimes is very expensive

3. Stiebel Eltron Tankless Water Heater – Tempra 20 Plus

The Stiebel Eltron Tempra 20 Plus Tankless Water Heater features the unique German proprietary Advanced Flow Control technology developed by Stiebel Eltron to regulate water temperature automatically for continuous comfort. If hot water demand exceeds, it can ensure that hot showers will never be interrupted, slightly reducing the flow. Compared with traditional electric tank water heaters, Tempra 20 Plus can usually use 15-20 percent less energy. But, depending on personal home use habits, it’s possible to save considerably more resources. The difference is that traditional tank water heaters store hot water continuously. As a result, they lose 15%-20% of the overall energy used by the environment around them. This is known as standby heat loss. The brand of this unit is the best electric tankless water heater brand in the market.

Stiebel EltronTempra 20 Plus

Key Features:

  • Digital display for accurate temperature setting
  • The solid copper heating chamber
  • Energy monitor showing cost saving
  • Made in Germany
  • Smart Microprocessor Technology
  • Advanced Flow Control

Perhaps less effective are tank water heaters that use gas or oil, so they often lose heat to the outside through their vents. This tankless water heater does not need venting and does not store hot water, waiting for you to use it. When you need hot water, it runs on-demand to provide constant and infinite hot water and doesn’t waste energy when you don’t need.

 Advanced Flow Control:

A standard feature in this model is Advanced Flow Control. If the demand is greater than can be met by the water heater, Advanced Flow Control works by significantly decreasing water flow automatically. Advance Flow control is an exclusive feature of this model; no other models or manufacturer has this kind of advance feature in their tankless water heaters.

Sleek Design saves Space and Energy:

Its compact, sleek white design saves space but still provides your entire house with endless hot water, and no venting is needed. With auto-modulation and the ability to electronically regulate water flow, the eco-friendly unit saves electricity. The Savings Dashboard also displays how much energy costs are saved. Its sleek design is the best small electric tankless water heater out there in markets.

 Easy Operation:

An electronic switch triggers this hot water heater, and it is noise-free when in operation. Has a digital display of temperature and preset temperature and memory buttons, while the internal solid copper heating system does all the power work.

 Self-Modulation Energy Technology:

Another feature this model has is the self-modulation feature. Self-modulation also has this model. Self-modulation is often confused with flow control; instead, it is mostly related to the amount of energy used to heat the water. Self-modulation also referred to as auto-modulation, which ensures that only the least amount of energy is used all the time.

Warranties Included:

Top-rated electric tankless water heaters from Stiebel Eltron perform to the highest expectations for comfort and reliability. The purchase includes 7-Year Leakage and 3-Year Parts Warranties.

  • Digital temperature control. Voltage: 240 Volt or 208 Volt
  • Proven reliability
  • No venting required
  • Easy to install
  • Energy efficient
  • The sleek design saves space and energy
  • Because of advanced tech, it is on the expensive side
  • May need an upgraded electric grid

4. Rheem RTEX-18 18kW 240V Electric Tankless Water Heater, small, Gray

This unit has most advanced self-modulation technology. It adjusts power to meet hot water demand and is very easy to install. This tankless water heater has external digital thermostatic control with led display (+/1 degree accuracy). It has durable copper immersion two heating elements, field serviceable. This units’ flow rate is up to 4.4 GPM. It also has some additional features such as threaded for easy replacement, simple installation, and digital temperature display makes it more efficient, durable and easy to use.

Rheem RTEX-18 18kW 240V

Key Features:

  • External digital thermostatic control with LED display (+/1 degree accuracy)
  • Most advanced self-modulation adjust power to meet hot water demand.
  • Durable Copper immersion two heating elements, field Serviceable. Flow Rate- up to 4.4 GPM
  • Simple installation – bottom 3/4 inch NPT water connections
  • Threaded for easy replacement, simple installation, digital temperature display

Water Saving Mode:

The water-saving mode is the main and additional feature of this unit, making it more reliable and efficient. This feature makes this unit one of the top the best tankless water heater. Ultra-Low NOx burner fulfils rule requirements of safety with low emissions of SCAQMD. Exclusive Guardian Overheat Film Wrap of this unit prevents it from reaching the dangerous temperatures.

Water on Demand:

This water heater provides fast, continuous hot water for single point-of-use or multiple applications, on-demand. Vital heating elements for copper immersion with a brass top improve longevity and are threaded for quick replacement.

Digital Temperature Control:

Digital regulation of temperature enables you to set the temperature at 1 ° increment.

  • Most advanced self-modulation
  • Digital temperature display
  • Reasonable Price
  • 99.8% energy efficient
  • The sleek design saves space and energy
  • There is some mistake with the mounting/wiring diagram that comes with the unit
  • Fluctuating temperature

5. 3M Aqua-Pure Whole House Scale Inhibition Inline Water System AP430SS,

To minimize scale build-up and corrosion, the 3M Aqua-Pure Whole House Scale Inhibition Inline Water System AP430SS is designed to help prolong the life of hot water appliances such as water heaters (standard (gas or electric) and tank-less), boilers, clothes washers and dishwashing machines, and plumbing fixtures such as faucets, pipes and showerheads. To bind calcium and magnesium hardness minerals, the AP430SS includes polyphosphates to prevent them from precipitating out (or becoming a solid) and building upon metallic surfaces. Polyphosphates also help to resist corrosion by creating a thin layer of protection on the metal’s surface. Polyphosphates help to inhibit scale build-up in water heaters (standard and tank-less styles) and appliances such as dishwashers and clothes washers which can help extend the life of hot water-using appliances.

3M Aqua-Pure Whole House

Key Features:

  • Rugged Stainless Steel Head: Rust and corrosion resistance.
  • Forced Feed Orifice: Proportionally doses media at a flow rate between 0.25-10.0 GPM.
  • 3/4″ NPT Connections: Allows maximum flexibility to adapt to plumbing.
  • Sump: Pressure range of 25-125 PSI.
  • 40 – 100°F/37.8°C temperature range
  • Flow rates up to 10 GPM/37.9 pm
  • 25 — 125 psi/172 — 862 kPa pressure range

The AP430SS’s overall single vessel/cartridge configuration makes it simple for professionals as well as end-users to adjust the 3M Aqua-Pure AP431 Water Filter Cartridge. If you experience a significant decrease in the water flow rate, adjust the disposable filter cartridge every six months or earlier. The AP430SS should be mounted on the water heater’s cold water supply line or at the point of entry of water into the water supply line.

Helps Protect Hot Water Heaters:

Polyphosphates, included in this product, help to inhibit scale build-up in hot water heaters (both standard (gas or electric) and tankless styles) and boilers; Helps extend the life of hot water heaters and hot water-using appliances, pipes, and downstream plumbing fixtures such as faucets and showerheads. This best electric tankless water heater is ideal for a home of any size.

Maintains Efficiency:  

The water heater efficiency is maintained by inhibiting scale build-up on heating elements

Easy To Replace: 

Easy change out of the 3M Aqua-Pure AP431 Replacement Water Cartridge makes system maintenance easier

High Flow Rates: 

3/4 Inch NPT Inlet/outlet connections for easy installation and high flow rates (rated for up to 10 GPM); System to be installed on cold water line feeding the water heater

Corrosion Resistance:

It is possible to mount 304 stainless steel heads on existing copper pipes at home. It consists of a material resistant to corrosion that provides the heater with long service life.

NSF, Slandered 42 Certified: 

NSF International tests this unit to NSF/ANSI Std; 42 for material and structural requirements only.

Product Specification:

The system has a pressure range of 25 to 125 PSI (862 kPa) and operating temperature of 40 to 100F (4.4 to 37.8C)

Scale inhibition

Scale inhibition also helps protect piping from corrosion

  • Easy cartridge change-out helps provide easy system maintenance
  • Flow-Through Design with negligible pressure loss.
  • Scale inhibition also helps protect piping from corrosion
  • It is required to Change the disposable filter cartridge every six months
  • Fluctuating temperature

6. Bosch Electric Mini-Tank Water Heater Tronic 3000 T 7-Gallon (ES8)

Bosch Tronic 3000 T electric point-of-use mini-tanks come in three lightweight sizes that can be wall-mounted (bracket included) or floor-mounted. They easily fit under a sink, even in a cabinet room. When placed in a noticeable position, they blend seamlessly with existing décor since they have a sleek and attractive design. Tap the cold water line and install the water heater to provide hot water directly to the sink. This best electric tankless hot water heater is very efficient for a wide variety of locations. It is the best rated electric tankless water heater.

Bosch Electric Mini

Key Features:

  • Provides hot water quickly at point-of-use
  • Electrical requirements (Amp 12A/Volts 120)
  • Dimensions : 17.5 W x 17.5 H x 14.5 D Inches
  • Units can be wall/floor mounted
  • Heating capacity of 1440 watts
  • temperature range of 65-145°F max
  • Operating pressure -150 psi
  • Glass-lined tank for long service life
  • 120VAC plug-in connection (1440 Watts)

With the Bosch ES8 Tronic 3000 T Electric Water Heater, get hot water where you need it when you need it. This mini-tank with 4 gallons of point-of-use space fits right under your sink and offers a practical and effective solution to your hot water needs. The glass-lined tank provides excellent insulation and additional resilience, while the heater’s quick recovery time prevents long hot water waits. You can easily monitor the temperature range with an external knob, and the temperature-and-pressure relief valve improves your protection. This unit removes long waits at your sink for hot water, getting hot water on demand at your every need (supplies up to 2 sinks at a time).

Convenient Hot Water Heater: 

7-gallon point-of-use mini-tank fits under your sink to provide hot water right where you need it. Thermal efficiency is 98%. 

 Installed Vertically Or Horizontally:

This larger model can be positioned vertically (7 gal. of water supply) or horizontally (5.1 gal. of water supply). The vertical orientation is mounted on top of the machine with the cold and hotlines.

 Reliable Water Source:

Easily hard-wire the 7-gallon model to provide the on-demand reliable water source with your home or office needs

Important information: 

This unit has a heating capacity of 1440 watts and a temperature range of 65-145°F max. Operating pressure -150 psi. Water fittings-3/4 inch Male NPT. Electrical requirements for this unit is (Amp 12A/Volts 120)

 Easily Mounted: 

It can be installed on the shelf, wall or floor (bracket included only for vertical orientation); tap the cold water line and place the water heater directly at the sink to provide hot water.

  • Temperature Control
  • Sleek and attractive design blends in seamlessly with any décor
  • CFC-free foam insulation offers maximum energy efficiency
  • 1140 Watt powerful motor provides hot water quickly at the point of use
  • Provides instant hot water and easy to maintain
  • Premium glass-lined material for a long service life
  • Leakage issue

7. Rinnai V65IN Tankless Water Heater

V65iN is one of the best natural gas tankless water heaters from Rinnai and is the best combination of high efficiency, comfort, and value. This unit of Rinnai is ideal for small to medium homes. It is compact, easy-to-install, reliable, and perfect for indoor locations. This unit provides peace of mind with warranties that transcend the competition. It provides endless hot water for your entire home. This unit is suitable only for Indoor Installation. V65iN is very highly Efficient Tankless Hot Water Heater.

Rinnai V65IN Tankless Water Heater

Key Features:

  • Up to 6.5 GPM hot water flow rate (varies by groundwater temp)
  • Control-R 2.0 mobile app features timers and schedules throughout the day and allows you to put the system into vacation mode remotely.
  • Residential Factory Warranty – 120 months (heat exchanger), 12 months (labor), 60 months (parts)
  • Concentric venting system
  • Temperature lock to prevent accidental or unauthorized changes to water temperature
  • Complies with South Coast Air Quality Management District 14 ng/J or 20 ppm NOx emission levels

Endless Hot Water

Now you can put an end to scheduling all your need for hot water. Rinnai V65IN Tankless Water Heater will never run out of hot water, and it does not leave you in the cold water. Now never choose between taking a hot shower, doing dishes, or doing laundry, because this unit can provide you enough water for all these domestic needs. No doubt this is the best natural gas tankless hot water heater, and it is a top-ranked water heater with many great reviews.

Hot Water On-Demand

V65iN tankless water heaters use the ThermaCirc360 technology to recirculate hot water through pipes to supply hot water fast. Don’t waste time waiting. Waiting for hot water when it travels from old tanks to shower, almost twenty-four 16-ounce bottles get wasted every time.

Save Valuable Space

This unit design is very compact and concise, which saves a lot of valuable space. It is suitable for even small homes. Due to its compact design, you can install this unit in non-traditional areas such as the attic, closets, and other small spaces. This unit, all other Rinnai tankless water heaters are only the size of a small suitcase, and this feature makes it the best tankless gas water heater for small homes.

  • Save time with hot water,
  • Suitable for any size home
  • for simultaneous uses at multiple fixtures
  • Maximum output
  • Minimum space
  • Suitable for installation in non-traditional spaces such as closets and attics
  • Energy Factor of 0.82/Uniform Energy Factor of 0.80
  • Best rated tankless gas water heater
  • Hard to install
  • Rinnai water heaters are quite expensive

8. Rinnai V65eN Outdoor Tankless Hot Water Heater

V65eN is the best combination of high efficiency, comfort and value. This unit of Rinnai is ideal for small to medium homes. This unit of Rinnai is compact, easy-to-install, reliable and perfect for outdoor locations. V65eN provides peace of mind with warranties that transcend the competition.

Rinnai V65eN Outdoor

Key Features:

  • Max BTU’s 120,000
  • Max Energy Factor 0.82
  • Outdoor Installations
  • Meets California and Texas NOx Emissions Standards
  • Outputs up to 150,000 BTUs of heating power at continuous 6.5 GPM
  • ENERGY STAR® qualified for increased efficiency and power usage
  • Certified for installation in mobile homes
  • Electronic ignition removes the need for a pilot light, saving you money in fuel costs.

From the manufacturer

Rinnai’s V65E exterior-mount tankless water heater efficiently delivers up to 6.6-Gallon per minute (GPM) of hot water, making it perfect for your one to two and a half bathroom home. This easy-to-install, ultra-compact unit lets you enjoy all the benefits of Rinnai tankless water heating. You’ll experience clean, reliable hot water at a consistent pre-set temperature while saving energy and precious floor space in your home.

Space Efficient 

Space can be valuable, especially if you live in an apartment or a smaller house. In this respect, you need a water heater that will not significantly reduce your living space. Rinnai Tankless water heaters are designed as compact wall-mounted devices that take up as little room as possible.

Not much bigger than a small suitcase, their wall-mounted tankless heaters can be installed both on the exterior and interior walls. Not only that, the smaller size means that water heaters can be installed in more creative places to save space, such as crawl spaces and small attics. This also means it can be installed in modular homes.

Affordable, Efficient Savings

V65eN design is very compact and efficiently packaged in its design cut CO2 emissions, which enable it to use less energy and preserve water. It uses 40% less energy than other traditional water heaters because it heats the water whenever needed.

Sustainable Reliability

Rinnai’s V65E is a smart investment for now and even for the future when you convolute durability and reliability. All parts of the V65eN Rinnai Tankless water heater are replicable, so all these components can be exchanged quickly rather than buying a new system. The life expectancy of V65eN is 20 years, which is far more than a traditional tank. This product will save not only your money but also energy.

  • Lightweight and Compact
  • Isolation valves sold separately
  • Maximum output, minimum space
  • Efficient Condensing Technology
  • Innovative technology provides an endless supply of hot water
  • Designed for outdoor use only
  • expensive

Plus Features:

  • Integrated temperature controller provides temperature range control from 98°F to 140°F
  • Ultra-low NOx emissions compliant
  • Vented with Rinnai’s Concentric direct vent system
  • Approved for use in altitudes of up to 10,200 ft
  • Isolation valves sold separately
  • The residential warranty offers ten years coverage on the heat exchanger, five years on parts, and one year on labor

Buying Guidelines | Features to Consider While Purchasing a best Tankless Water Heater

To choose a tankless water heater based on features that will be most beneficial to your home, keep in mind the following:

best tankless water heater buying guides

Water heaters consume almost 20 percent of any household budget. Other than this expense of water heaters they can break and leaves your basement flooded, and no more hot water for you.

Suppose your water heater is near its end, and you need to exchange your water heater. In that case, you have a better choice of tankless water heaters, which reduced the consumption of energy and have so many advantages such as endless hot water and a smaller impact on the environment, the size of a tankless water heater is minimal and compact. It also comes with replaceable parts, and most importantly, they supply hot water whenever needed. Tankless water heaters are far more efficient than traditional storage water heaters.

Consider Capacity

Before buying the water heaters, you should consider the capacity of the water heaters. It would be best if you chose them according to your need for water. A family of four might need more water supply than any other smaller households because they might use several showers, run the dishwasher, and wash a load or two of laundry in an average day. So, capacity is an essential feature that should be considered before buying the system. 

Features to Consider


You should choose the tankless water heater with the longest warranty. An average water heater runs almost 12 years, but the units with the longest warranty have larger burners and elements than the heaters with the shortest period’s warranty.

Anti-scale devices:

 Some brands offer units that have mineral scale units to reduce the buildup, but this breaks the unit in the shortest period of time. So, you shouldn’t go for the fancy features if they can cause the unit’s life. It would be best if you chose long-lasting units that last at least 12 years.

Brass vs. plastic drain valves:

Choose the units with brass drain valves because they are more durable than the plastic drain valves.

Glass-lined tanks: 

Glass-lined tanks are designed to reduce corrosion.

Digital displays:

This will help you to adjust the temperature of the system more efficiently. It also displays collector temperatures, pressure readings, and other information about the unit. You can also set vacation mode, which makes tankless water heaters more efficient.

Fuel Type:

There are three main types of fuels for tankless water heaters: natural gas, propane, and electricity. Best gas tankless water heaters operate at a higher power output as compared to electric tankless water heaters. 

  1. Natural gas: It usually costs less than propane or electricity and, in many homes, can be directly piped in. This tankless water heater is an excellent long-term investment, as the lower cost of natural gas can eventually make up for the higher price of the unit. 
  2. Propane gas: It is the most expensive and often cannot be piped into a home. Instead, a tankless water heater that runs on propane is typically fed by a portable fuel tank, positioned directly next to the water heater. 
  3. Electric: Electric tankless water heaters are affordable, both in terms of initial purchase and installation.

Flow Rate (GPM):

The flow rate of a tankless water heater represents the overall hot water volume that the tank can generate. For each fixture, for example, the bathroom tub or the kitchen sink, the flow rate is measured in gallons per minute, or GPM, requiring a certain amount of flow to function as expected. A tub uses about 4 GPM, for instance, while a shower uses approximately 3 GPM.

Remember the amount of water used all at once in the household when deciding your home’s flow rate and your individual needs. A lower flow rate is sufficient if few fixtures are ever in operation at one time. If several showers, a dishwasher, and a few sinks are likely to operate concurrently, a lower flow rate will fall behind the home occupants’ requirements.

Power Input (BTU):

The energy needed to heat water to a target temperature is called the input of electricity. In British thermal units or BTUs, this is measured. A BTU refers to the amount of energy provided by one degree Fahrenheit to increase one pound of water temperature. Consider a simple situation to decide on the appropriate power input for your tankless water heater. Assume that the water is coming into your home at 40 degrees Fahrenheit and that you would like your shower to contain water at a temperature of 120 degrees Fahrenheit. It would be appropriate for the tankless water heater to lift the temperature by 80 degrees. It would require 667 BTUs per gallon to do so.

At 2.5 GPM or 150 gallons per hour, a shower works. A tankless water heater will need to generate 100,000 BTUs per hour to heat 150 gallons of 40-degree Fahrenheit water to a temperature of 120 degrees, assuming 100 percent performance and a single fixture is in use. The minimum BTU requirement goes up if the efficiency level decreases or another fixture is added.


Gas tankless work by fuel combustion. It generates exhaust when fuel burns, which must be vented outside the house, away from doors, windows, or any frequently used environment by individuals or pets. The installation of ventilation pipes, depending on the circumstances, will increase the installed cost of a tankless water heater.

Condensing vs. Non-condensing

A by-product of the fuel burning in a gas tankless water heater is steam or water vapor. By ducts or piping, the steam is released to the outside. The distinction between condensing and non-condensing is when unique steam is released as part of the ventilation process. 


Non-condensing tankless water heaters vent steam automatically. This includes the use of ventilation materials that can withstand elevated temperatures. These quality materials come at a cost, so rates for installation may be higher. The heat lost by immediate ventilation often results in an efficiency rating of only approximately 80-85%. Water heaters that are non-condensing are usually easier to buy.


There is a condensing unit for condensing tankless water heaters that absorbs and reuses the residual exhaust heat before releasing a much cooler exhaust to the outside through ventilation channels. This style costs more money but provides efficiency of about 98 percent.

Our Suggestion

Frequently Asked Questions about Tankless water Heater.

1) What is a tankless water heater?

Storage tank water heater keeps water hot 24 hours a day, even when you don’t need or using hot water. But on the other hand, a tankless water heater does not store hot water. It heats the water whenever you need it.

2) How a tankless water heater works?

The heater of tankless water heater is triggered by the flow of water whenever you open a faucet. If you use gas heaters, then powerful gas burners will turn on and will rapidly heat the water as it passes through the heater and the same with the electrical.

3) What are the benefits of a tankless water heater?

A tankless water heater consumes the energy only when you are using the hot water because it heats water only when you open a faucet and gets turn off or stop heating the water when you turn off the faucet. 

4) How much money can I save?

If you are already using a storage tank water heater if it runs on gas or electricity, you could save from 5% to 69% off of your water heating bills. It also depends on the model of tankless water heater you use and also on the size of storage tank. 

5) Will one tankless water heater be enough for my entire house?

Yes, this depends upon the size and model of the tankless water heater that you purchase for your home. You have to choose the proper model to suit your home’s need of hot water.

6) Is it possible I can get hard water?

As it is already discussed that there is no storage of water in tankless water heaters, so there are fewer chances for minerals to settle out of the water column, and it can build up inside the heat exchanger. There is no harm in using a water softener with a tankless water heater.

7) Can I use a tankless water heater for other domestic appliances?

Yes, it is possible to use a tankless water heater for other applications such as washing machines or dishwashers. For this, you have to use a mini-storage tank in-line with your main water heater. 

8) Are there other advantages of a tankless water heater?

Yes, of course, there are so many advantages of using a tankless water heater. Other than the money savings, endless hot water, and smaller impact on the environment, the size of a tankless water heater is very small and compact that you can easily install it even in small places, or you can easily hang them on the wall, which will save valuable space on the floor.  

9) Is tankless water heater suitable for those who live in an area with high altitudes?

Electric units are suitable for homes in areas of high altitudes because they are not affected by higher altitudes. But tankless water heaters will not function as effectively in these.

10) Is this a new technology?

No, it is not a new technology; in North, America people are using tankless water heaters for 75 years now. But now it’s been using all around the world and no doubt this technology is replacing storage tank water heaters.

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