Best High-Efficiency Gas Boilers Review in 2021 – New Edition

Best High Efficiency Gas Boilers Review

LAST UPDATED: January 13th, 2021

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Are you fed of your low-quality gas boiler because it’s hiking up your electric bill? Well, this is because you don’t own a high-efficiency gas boiler, and urgently need a replacement. We know it can be pretty challenging to find a trustworthy product in this day and age.

So, to make sure you don’t make a wrong decision, we have carefully listed the ten best high efficiency gas boilers with highly beneficial features. The problem with regular gas boilers is that even though they don’t cost much, they drain so much energy that it can empty your pockets for the rest of the year.

The best-rated high-efficiency gas boilers listed in this article will not only give you instant hot water on demand but also save energy.

Best Gas Boilers Comparison in 2021

Last update on 2021-04-17 / Affiliate links / Images from Amazon Product Advertising API

Why Is High Efficiency Important?

High efficiency is of the utmost importance when purchasing a gas boiler. It determines the amount of energy it needs to consume to function properly. Gas boilers with a high efficiency factor consist of features that save energy. As a result, it will save you a lot of money in the long run.

It will also help you get hot water instantly on-demand, regardless of the number of fixtures in your house. High-efficiency gas boilers offer superior performance and usually require less maintenance. This also saves you money and is practical evidence of its quality. High efficiency also ensures the gas boiler will last longer.

High Efficiency vs. Standard Efficiency

Gas boilers with an efficiency rating of 80% to 84% are known as standard efficiency boilers. These gas boilers are equipped with cast iron heat exchangers and tend to vent using the chimney. Standard efficiency gas boilers usually have two types of venting systems – power vent or direct vent.

Power vented boilers use a fan to send the air out of your home. Direct vented gas boilers push the air out with the help of a pipe inside your house. These might be cheaper than high-efficiency boilers but are certainly not as reliable.

High-efficiency gas boilers, equipped with a stainless steel or aluminum heat exchanger, have energy efficiency ratings of over 90%. Its heat exchangers are more durable than others. Most of the high-efficiency boilers use a direct vent to push out the air.

These boilers have excellent energy saving capabilities and can cut down heating bills. They also have environment-friendly features. Although they are pretty expensive, they are surely worth the money.

10 Best High-Efficiency Gas Boilers Review

There is no lack of choices when you’re scouring for the best high-efficiency gas boiler. To make sure you don’t end up putting your money down the drain, we have handpicked the ten best high-efficiency gas boilers available for purchase.

Rinnai V Series Tankless Hot Water Heater

Rinnai V Series Tankless Hot Water Heater

We start off this list with this smart and efficient tankless water heater. It sufficiently provides you with hot water whenever you need it. You no longer have to plan your water usage and get overloaded with chores. This reliable water heater will never run out of hot water.

Another highly beneficial feature allows you to get instant warm water on demand. With the help of ThermaCirc360 technology, hot water is recirculated throughout your plumbing system. This prevents significant water wastage and can help you save up to 8700 bottles of water per year.

Despite its numerous features, this V Series tankless water heater flaunts a compact design. It takes up a minimum amount of space. Thus, it can be set up in almost any area of your household. It only takes up as much space as a small suitcase!

Moreover, its compact design will benefit you in more ways than you think. Water heaters that include large tanks emit more carbon dioxide. This tankless water heater not only reduces CO2 emissions but also requires less energy to operate.

To make your job even easier, it offers you full control with a mobile app of its own. You can set it on a timer, and also put it in vacation mode. This best-rated high-efficiency gas boiler will provide hot water at a constant 6.5 GPM.


  • Limitless hot water
  • ThermaCirc360 saves water
  • Reduced CO2 emissions
  • 6.5 GPM flow rate


  • Complicated installation

Rheem RTGH-95DVLN Tankless Water Heater

Rheem RTGH-95DVLN Tankless Water Heater

This next model is one of the best natural gas boilers on the market. What sets it apart from other gas boilers is its stainless steel heat exchanger. It relies on condensing technology to heat the water to a desired temperature. This specialized heat exchanger also makes this water heater 94% energy efficient!

If this isn’t a remarkably efficient water heater, I don’t know what is! It’s also environmentally friendly as it produces negligible emissions. People living in cities with low emission restrictions will find it more beneficial. They also include a remote control device, which lets you monitor the heater effortlessly.

But unlike with other gas boilers, this smart remote allows you to control natural gas usage. This promotes better efficiency as it will save energy. Apart from that, you can also monitor the temperature of the water with this device. A maximum temperature setting prevents water from being getting scalding hot.

Furthermore, this exclusive model introduces a unique feature. This gas boiler is wrapped in a modified film (called guardian film), which prevents it from overheating. It makes the boiler more durable and saves it from permanent damage.

Freeze protection in the water heater makes it suitable for use in colder regions. It keeps prevents the pipe water in the pipes from freezing and can withstand up to –-30 degrees Fahrenheit of temperature.


  • 94% energy efficiency
  • Remote control saves gas usage
  • Guardian film
  • Freeze protection


  • Extra costs for repair parts

Takagi T-H3-DV-N Natural Gas Water Heater

Takagi T-H3-DV-N Natural Gas Water Heater

The T-H3-DV-N model is a revolutionary addition to this list of best high-efficiency natural gas boiler. Unlike most gas water heaters that have a maximum flow rate of 8 GPM, this model offers a 10 GPM constant! It’s so smartly designed that the internal heat exchangers start working as soon as it detects cold water.

A rather distinguishing feature of this heater is it uses a unique condensing method to raise the water temperature. It has a combustion chamber where the steam is condensed and converted into water. The water then flows down a drain and flows through your in-house pipes when you need it.

It has also been programmed with a number of safety features. Hence, it reduces the risk of overheating.
Ironically, it is capable of heating the water up to 185 degrees Fahrenheit! This powerful water heater is capable of providing 10 GPM of the flow rate through every shower and sink, even when they are running simultaneously.

Heat transfer capabilities are also enhanced for this device. The heat exchanger is made up of copper alloy instead of the stainless steel material used by most water heaters. On top of that, it operates in complete silence regardless of being so powerful.


  • Constant 10 GPM flow rate
  • Heat exchanger made of copper alloy
  • Utilizes a condensing system
  • Can heat water up to 185 degrees Fahrenheit


  • Heavy and complicated to install

Rinnai RUC98iN Ultra Series Tankless Water Heater

Rinnai RUC98iN Ultra Series Tankless Water Heater

Next up on the list is this exclusive RUC98iN model with energy-saving capabilities. It requires 50 percent less energy to operate due to the use of heating coils. As the water passes through the heating coils, the temperature rises. Therefore, it doesn’t consume much energy for heating the water.

This brilliant model is equipped with a much more precise temperature monitor. It helps you set the water temperature that suits you best. They also introduced both PVC and concentric ventilation systems.

Condensing technology has been implemented to make the heating process faster and smoother.
The Ultra Series water heater uses very little gas per day even though it heats water pretty fast. Moreover, it can be easily installed without much experience. But make sure you take some safety precautions.

What’s impressive, though, is its excellent energy efficiency factor of 0.96! That’s more than any other model on this list. Despite packing all these features in one gas boiler, the manufacturers have managed to make it compact. It can easily fit in almost any corner of your household. Once switched on, it does its job relentlessly without even making a sound.

Since it’s tankless, you don’t have to worry about water running out. It takes water directly from the tank, so you get a constant supply of warm water.


  • Requires 50 percent less energy
  • Can be installed easily
  • Energy efficiency factor of 0.96
  • PVC and concentric ventilation


  • Heating takes time after staying idle

Eccotemp i12-NG Tankless Water Heater

Eccotemp i12-NG Tankless Water Heater

The stylish black finish and smart modernized design of the i12-NG water heater are what catches your eye at first sight. It has a sleek outlook, and the front panel is made of black tempered glass. The LED display registers an accurate reading of water temperatures and flow rates.

It allows you to select the temperature using just your fingers! You can hardly find a water heater with such an effortless design. It even adds to the aesthetics of your household. This stylish water heater generates a moderate flow rate of 3 GPM and is suitable for heating small to medium amounts of water at a time.

It will still enable you to use multiple water appliances at the same time. The water heater is also durable as it is equipped with a stainless steel vent kit. This is also energy efficient as it only consumes 1.07 Amp while running. A meager 2 watts is used while idle.

However, it has two different temperature settings. The tankless natural gas boiler can heat water up to 40 degrees Fahrenheit while running at 3 GPM.

At 1.5 GPM, it can raise the water temperature to about 77 degrees Fahrenheit. Both the temperature and water flow are fully automated and can be controlled using the LCD monitor.


  • Sleek design
  • LCD display with temperature and flow rate monitor
  • Only consumes 1.07 Amp
  • Can raise temperature up to 77 degrees Fahrenheit


  • Not suitable for large household

Marey Power Gas 10L Tankless Water Heater

Marey Power Gas 10L Tankless Water Heater

Running on 2D battery cells, this tankless water heater doesn’t require electricity to operate. A double ignition device utilizes ions to detect the flame and constantly raises water temperature. The system is known for its sensitivity and makes the gas boiler convenient to use.

They use clever anti-freezing technology to keep the water from freezing due to cold climates. When the temperature decreases drastically, the water is kept inside the internal pipes by discarding the discharge valve. The combustion system is designed to keep the flames lively during winter.

A summer/winter switch enables you to control the internal temperature during both climates. This helps you save more energy and keeps the electricity bill low.

As it only needs 8 PSI of pressure to operate, transferring warm water to upper levels is easier. The gas supply also automatically turns off in case the flame goes out.
This makes sure the device lasts longer and more effectively.

Due to the extensive use of natural gas, carbon emissions are almost negligible. Thus, this is one of the most environmentally friendly water heaters out there. It also keeps the water fresh for consumption because it’s unlikely to rust.

It gives a constant supply of hot water for both drinking and cleaning purposes. The water supply is safe, warm, and pure.


  • Uses 2D cell batteries
  • Isn’t affected by a temperature drop
  • Doesn’t rust
  • Minimal greenhouse emissions


  • Needs a sufficient flow rate

Ridgeyard 18L 4.75 GPM Tankless Water Heater

Ridgeyard 18L 4.75 GPM Tankless Water Heater

Coming in at number 7 is this 18L water heater. This water heater allows you to get instant hot water on demand, once it is installed. Installation isn’t that tricky and can be done without a hassle. You don’t need to be an expert electrician to assemble this device, but some expert supervision is recommended.

The water flow rate of this tankless water heater is 4.75 GPM! That’s pretty impressive when you consider how much it can contribute to your convenience. It is powered by 2D cell batteries and, uses an automatic electrical pulse ignition to operate. Regardless to say, it saves energy to a certain extent.

This model boasts an exceptional stainless steel panel that is capable of resisting corrosion. It keeps the internal components working effortlessly for a longer duration. The panel also includes an LCD screen that displays the temperature of the water. You can use knobs to monitor the temperature as you desire.

If this isn’t enough to win your trust, you’ll be glad to know that this natural gas boiler is CE certified. It implements manifold auto protection for the maximum safety of the user. They also included a smart feature that shuts off the heater when the temperature reaches over 75 degrees Celsius.


  • 4.75 GPM flow rate
  • Stainless steel panel
  • CE certified boiler
  • Overheat protection


  • Can only be installed in certain places

Tengchang 10L 2.6 GPM LPG Water Heater

Tengchang 10L 2.6 GPM LPG Water Heater

As the next addition to this list, we have brought you this LPG powered water heater. With a thermal efficiency of 80%, this natural gas boiler can sufficiently heat water up to 25 degrees Celsius. It runs on a modified combustion technology, which specializes in reduced gas usage.

This helps you save a lot more money in the long run. The heat exchanger, along with the burner, has also been improved to muffle the burning noise. It’s pretty surprising that such a powerful device can run so quietly. This is a perfect choice for people living in areas with low water pressure.

Even people living on the upper floor will get a constant supply of hot water, regardless of the water pressure. The specialized water linkage valve in the device makes this possible. It also introduces manifold auto protection as an extended safety measure. This water heater is as safe as it is efficient.

Another clever characteristic of this LPG gas boiler is its ion inspection. It can detect if and when the flame goes out and instantly turns off the gas supply. This is an added safety measure to keep the heater from unwanted combustion. It also uses over water pressure protection to your advantage.
It can reduce the water pressure automatically when the pressure exceeds the limit.


  • 80% thermal efficiency
  • Reduces gas consumption
  • Manifold auto protection
  • Overwater pressure protection


  • Some of the models don’t last long

Westinghouse 11 GPM Condensing Water Heater

Westinghouse 11 GPM Condensing Water Heater

Fitted with dual stainless steel heat exchangers, this condensing water heater is the best of its kind. It’s built to withstand corrosion and is durable enough to last a decade. A constant flow rate of 11 GPM ensures that you will get a steady supply of hot water throughout your house.

Hot water will pour through the sink almost instantly after starting the operation. Regardless of the number of water applications, this reliable model will provide you with the perfect temperature of the water supply. This model can deliver up to 199,000 BTU of uniform power!

The immense amount of power makes it more suitable for large households with multiple fixtures. It also has a superior energy efficiency of 98%. This condensing water heater also comes with an easy to use LCD display. It allows you to control not only the temperature but also the rate of flow.

Furthermore, tThe monitor is easy to read and even more convenient to control. You can even switch between Celsius and Fahrenheit measurements of temperature. If the device runs across a problem, it will even show you an error message. It’s also equipped with a gas leak detector to ensure the utmost safety.
As an added precaution, and to prohibit water wastage, it comes with a water leak detector as well.


  • 199,000 BTU of power
  • 11 GPM flow rate
  • LCD display monitors temperature
  • Gas and water leak detector


  • Requires professionals for installation

Stiebel Eltron Tankless Water Heater

Stiebel Eltron Tankless Water Heater

The final entry to the list is this brilliant model of a tankless water heater. Manufactured in Germany, this is a top gas boiler with features to admire. This incredibly smart water heater offers you hot water on demand, no matter how many fixtures you have in your household.

Once it’s set up and starts operating, you will get a steady flow of hot water supply throughout every water appliance in your house. It’s built-in such a way that it doesn’t drain power when you’re not using it. This unique feature will help you cut down on your electric bill at the end of the month.

Even though it’s such a potent water heater, it has a compact size, which makes it easy to install almost anywhere. It has a sleek and simple design that’s easy on the eyes as well. This high efficiency gas boiler is so eco-friendly that it doesn’t even need venting.

The internal heating system is made of copper and carries out the heating process effectively. Water temperature is displayed on a digital monitor, which makes it easier to read. As it uses an electronic flow sensor to be activated, it doesn’t make any unnecessary noises.

This fully automated water heater can heat water anywhere between 86 degrees to 140 degrees Fahrenheit. However, it requires a constant 200 Amp to operate.


  • Instant hot water on demand
  • Doesn’t drain power when not in use
  • No venting needed
  • Electric flow sensor


  • Fairly pricey

What to Look for Before Buying?

Despite reading all the high efficiency gas boiler reviews, you’re still not prepared enough to make the best choice. To help you even further, we will discuss the key features to look when buying a gas boiler.

Condensing vs. Non-Condensing Boiler

Condensing boilers are more energy-efficient and environmentally friendly. It’s capable of working at low temperatures and still gives excellent results. A condensing boiler cleverly utilizes the water vapor produced during the heating process. Instead of discarding it, the water vapor is used to preheat the water.
This saves a lot more energy in the long run. On the other hand, non-condensing boilers require a venting system that just pushes the vapor out of your house. Condensing boilers are certainly more efficient.

Boiler Size

When choosing a boiler size, there are several things you need to consider first. The size of the gas boiler will depend on the number of water applications in your home. If the boiler is too small, it won’t be able to supply hot water sufficiently. On the other hand, a large-sized boiler will consume more energy.
The size will also depend on how thick the walls are. Even the insulation in your house is a crucial factor to consider. However, there are some models that are compact and still have a high heating capacity.

Boiler Efficiency

The efficiency of the boiler is indicated by the AFUE rating. Gas boilers with a rating above 90% have high efficiency. These models will not only make the heating process faster but also consume less energy while doing it. They also tend to last longer and need less maintenance.

Additional Features

Due to modern technology, several innovations have been made to modify water heaters for user convenience. New models have introduced digital control panels, which let you adjust the temperature. Some even include a feature that automatically turns the gas off when the flames burn out.
There are also several designs to choose from, so you can choose one that’s aesthetically pleasing as well. These little features will help you get additional benefits that might make it suitable for you.

Gas Boiler Terms to Know

When you think of buying a gas boiler, you might come across some general terms you have no idea about. To make sure you aren’t uncertain about the product, you should know what these terms really mean.

What Is AFUE?

AFUE is a common abbreviation for Annual Fuel Utilization Efficiency. This is a percentage ratio that compares the input and output of the unit. It gives you a general idea about the efficiency of the model. Gas boilers that have AFUE rating over 90% are called high-efficiency gas boilers.

Energy Star Gas Boilers

To achieve the Energy Star decree, a gas boiler needs to hold an AFUE of above 90%. This will tells you whether the gas boiler is based on the U.S Department of Energy standards. Make sure you compare this attribute among the models to get the most reliable one.

What Is BTU?

BTU stands for British Thermal Unit and is used to measure the heat output of gas boilers. Most residential gas boilers produce output between 40,000 to 150,000 BTUs. Gas boilers with 400,000 BTUs and above are more suitable for heavy-duty commercial use.

Absolute Pressure

The pressure above zero, and is a sum of gauge pressure and atmospheric pressure.

Air Atomizing Oil

This represents a burner that fires oil atomized using compressed air. Compressed air is passed through several streams of oil, which converts it into a fine spray.

Air Fuel Ratio

The volume ratio of air to fuel.

Air Purge

This defines the removal of unnecessary materials by replacing them with air.

Air Vent

This is the opening at the topmost part of the drum of the gas boiler, which lets out air from the house.

Allowable Working Pressure

The amount of pressure the boiler is built to withstand. Pressure control features in some models are designed to kick in when this pressure is reached.

Frequently Asked Questions

How long do gas boilers last?

A good high efficiency gas boiler can last from a decade to up to 30 years! Boilers equipped with stainless steel or aluminum heat exchangers tend to last longer than cast-iron models.

How do steam boilers work?

In steam boilers, hot fuel is passed through the water to convert it into water vapor. It is designed to direct the vapor towards your in-house radiator. After a while, the vapor cools off and is converted back into the water, which can be accessed by you.

Is a furnace the same as a boiler?

Even though furnace and boilers work in similar ways, they have a major difference. A furnace is used to heat air, whereas a boiler is used to heat water.

Is propane cheaper or electric?

It is cheaper to install an electric heater rather than ones that use propane. However, the energy bill will depend on where you’re living. Even though electric models have a high AFUE rating, they may hike up the energy bill.

Do natural gas boilers run on propane?

You will need to hire a boiler repairman to convert the natural gas boiler to use propane.

Final Words

By now, you probably have a general idea about what a good gas boiler is, and the things to look for when buying them. This will help you determine which of the aforementioned gas boilers are most suitable for. So, pick your water heater accordingly.

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