Indirect Water Heater vs. Tankless

Indirect Water Heater vs. Tankless – Comparison of 2023

Whether you are planning to install your first water heater or wish to replace an existing unit, you might be alarmed by the number of options you have to choose from.

From old storage type heaters to conventional tankless units, the world of water heaters has come a long way, and it’s hard to imagine that single heater that “beats them all.”

But one thing is certain;water heaters today are far more efficient and cost-effective than what they used to be.

Two of the most common options that exist for households are tankless and indirect heaters.

In this article, we are going to doa comparison of indirect water heater vs tankless. We will look at the benefits of both units as well as their limitations.

There will also be a review of the top 5 five products in each category so you can find a unit to meet your home needs regardless of the heater type you settle for.

Without wasting any more time, let’s hit the review!

Indirect Water Heater vs. Tankless – Comparison in 2023

Indirect Water Heater

Although not for everyone, an indirect water heater is one of the most efficient solutions available for domestic hot water supply.

Unlike tankless heaters, they come with a water tank and have a lower upfront cost.
Also, their recovery rates tend to be higher than what you get with regular storage tank heaters.

As a result, they are able to provide more hot water on demand.
These heaters are called “indirect” heaters because they do not generate their own heat but rather draw from the boiler in your home.

The heat exchanger coil inside the heater then uses the heat from the boiler water for its heating.

In other words, indirect water heaters work with the existing boiler or furnace in your home to supply domestic hot water.

Here are the core benefits or features of the heater:

Superior Installation

An important requirement of indirect water heaters is efficient insulation to eradicate the need for a blanket. As a result, heat loss is greatly minimized.

Ample Hot Water Storage

Indirect heaters are usually supplied with a tank thatcan store a large amount of hot water.

This ensures you have a higher output (compared to other heater types) and never run out of hot water throughout the day.


Wonder why the service assurance on indirect heaters usually lasts a lifetime? It’s quite simple – they are extremely durable,in fact, more durable than other systems.

This shouldn’t come much as a surprise considering the fact they don’t take much abuse like other types of heaters. The use of stainless steel for the construction of most boilers is also another reason.

Related Guide: Boiler vs. Tankless Water Heater

Saves a Lot of Money

By using an external source for power, indirect heaters are able to save you a lot of money in the long run.

Recommended Indirect Water Heaters to Buy

If you find an indirect water heater more appropriate for your need, then you would want to purchase the best unit.

With this in mind, we’ve reviewed the top five products in the market at the moment.

1) Burnham AL35SL Alliance SL Indirect-Fired Water Heater

When it comes to domestic water heating, indirect water heaters serve as a much cost-effective alternative to traditional storage tanks.

One model that seems to outclass competitors in terms of price is the Burnham AL35SL Alliance.

Althoughthis heater is cheaper than many other options, it still offers fairly good quality and performance.

So if you’re operating on a low budget but still need something that will not disappoint, then you will not go wrong with this unit.

The Burnham AL35SL has a 35-gallon capacity, which makes it a great choice for average-sized households. But even large homes can benefit from the heater depending on the water demand.

Like any other indirect heater, it is designed to be energy efficient, so you can expect a significant cut in your monthly energy bills.

Despite its low price, the heater still comes out sturdy. It is built with durable materials, which makes it long-lasting.

However, regular maintenance and cleaning arerequired to ensure the proper functioning and prevent buildup in the heating coil.

Theheater also boasts of high heat retention – thanks to its polyurethane foam insulation and solid metal construction. Heat loss is very low, and there’s no chance of corrosion occurring.

Installation is easy and only a small space is required.
Overall, this is an excellent heating unit that works great for medium to large households. It comes highly recommended.


  • Corrosion-resistant hydra stone lining
  • Easy to install and clean
  • Comes with a heating coil
  • Energy-saving (30% over conventional options)
  • Affordable price


  • Only one size option

2) Triangle Tube SMART80 Phase III Indirect Water Heater

The Triangle Tube SMART80 is another budget-friendly indirect heater specifically designed to cater tothe needs of large households.

It has a pressure drop rating that is considered one of the lowest in industry, and an energy efficiency that is unrivaled by many indirect heaters in the same price range.

So if you need a unit to provide abundant hot water in your home without much upfront cost, then this is the unit to go for.

One of the things we like about this heater is that it is outfitted with a self-cleaning heat exchangerthathas the ability to descale once contamination builds up to avoid rust and similar issues. This saves you from a lot of maintenance work.

Its tank-in-tank construction helps to preserve the high temperature of the hot water while preventing the growth of bacteria.

Although 70 gallons is the specified capacity, the heater also adds another 14 gallons, which totals up to 84 gallons – you now know why we say this is ideal for large households.

You will not get an endless supply of hot water, but you will get it at a high and consistent rate.

To retain temperature for a longer time, the heater is insulated with polyurethane foam, which is known to very effective.

Overall, we are impressed with SMART80, an excellent choice for its price. It is easy to install and has great customer support. We have no doubt you will come to appreciate the unit.


  • Durable components
  • High heat retention (double wall insulation)
  • Removable top makes cleaning easy
  • Efficient tank-in-tank design
  • Easy to install


  • Heating coil is not included

Heat-Flo HF-40 Stainless Steel Indirect Water Heater Tank

Another indirect heater that seems to provide a good bang for its price is the Heat-Flo HF-40 by SunnyHome.

WhileSunnyHome is not the most popular brand out there, there’s no doubt they’re a respectable brand with a solid reputation in delivering quality domestic heating solutions.

The Heat-Flo HF-40 is without doubts one of the best offerings from the company so far.

The heater is outfitted with a porcelain heating coil, which allows for easy cleaning. It also features a lid at the top and bottom for enhanced regulation of temperature and prevents overheating.

The lid also provides easier access to the heating coil when you want to perform cleaning or maintenance.

Also, the body of the heater is constructed with stainless steel and features a powder finish within and without for better heat retention and easy maintenance.

We are also impressed with how the heater looks. It is designed to fit right into your space. Installation is easy – thanks to the easy-to-understand manual provided with the unit.

People with some DIY experience should be able to get by if they decide to undertake the installation alone. However, we still recommend hiring an expert to avoid any issues.


  • Easy to clean
  • Comes with remote control
  • Installation is simple
  • Great customer support
  • Low heat loss


  • Not recommended for big families (40 gallons capacity)

3) Westinghouse 80 Gal. Electric Water Heater

The Westinghouse 80-gal capacity water heater is a decent unit specifically designed to meet the high daily hot water demand in larger homes.

As expected,the unit is highly energy-efficient and so doesn’t consume much electricity while fulfilling long draws of hot water. So you can expect to save a lot of money on your energy bills in the long run.

One of the areas where this unit stands out is in the provision of an adjustable thermostat, which allows users to control the temperature easily.

This also includes a high limit control, which helps to ensure there’s no overheating.
Thus, all you need do is set the desired temperature; and once this is reached, it automatically turns off.

It will also interest you to know that the stainless steel tank is lightweight and features outlet connections to allow for easy installation.

You will be glad to know that the energy factor is 0.94, which simply means almost all the energy entering the unit is used for heating.

In the end, you end up saving much more money as compared to using a conventional storage tank system.

Overall, this is an excellent heater that promises to provide good value for your money. It comes highly recommended!


  • Durable stainless steel construction
  • Very easy to maintain
  • Compact design
  • Large storage (80-gallon capacity)
  • Reliable customer support


  • A bit pricey

4) Rheem MR50245 Marathon Tall Electric Water Heater

To round up the list is the Rheem MR50245 Marathon Water Heater. This is without doubts one of the best electric indirect heaters out there.

You can easily tell this is one gem of a heater when you read the number of positive reviews it has online.

One of the features that make this unit stand out from competitors is the use of blow-molded polybutene (PermaGuard) for the construction of its storage tank.

With this non-metallic material, there’s no need for an anode rod, and you don’t have to worry about corrosion.

Also, without any anode rod, less maintenance is required, and you don’t have to worry about having any smelly water problem.

The heater is lightweight and can store up to 50 gallons of water, which makes it a great replacement for a traditional tank unit.

You will be glad to know it has an energy factor of 0.90-0.94, which is quite impressive. Also, the upper element of the heater is thermally fused to prevent dry-firing.

Overall, the Rheem MR50245 is a highly durable unit that promises to provide a lot of value for your money.


  • Highly durable
  • Energy efficient
  • Comes with a brass drain valve
  • Easy to install and maintain
  • No need for anode rod
  • Cons


  • Pricey

Tankless Water Heaters

As the name suggests, a tankless water heater is one that operates without a tank.
In a traditional tank, water tends to deplete quickly, depending on demand.

Here, once the water drains outs, users have to wait till another supply is heated and the tank is filled again.

In contrast, with a tankless heater, there’s no need to wait for a tank to heat before you get hot water.

Instead, it heats the water on demand (i.e. while you’re using the shower or faucet). For this reason, a tankless heater is often called an instantaneous or on-demand heater.

The incoming water passes through its heat-exchanger coils and comes out as hot water.

Like many other types of heaters, a tankless heater can use gas or electricity. Some of the features of benefits of using a tankless unit include:

High Energy Saving

With a tankless unit, you can save up to 60 percent on your bills as compared to a traditional storage tank.

Little Maintenance

Since there’s no tank, little maintenance is required. And you won’t have to worry about replacing the tank every now and then.

On-Demand Heating

This is probably the most important benefit of using a tankless heater. You get hot water when you need it (though, in reality, you might have to wait for a minute or two).

This is definitely more convenient than using a conventional tank heater where you have to wait for an hour or more once the water in the tank is used up.

Space Saving

Since the unit doesn’t require a tank, you need less space for installation.

Recommended Tankless Water Heaters to Buy

So what are the best tankless water heaters to buy? Let’s review the top five products.

5) Rinnai RUC99iN Sensei Tankless Water Heater

When it comes to the world of tankless heaters, many consider Rinnai to be “master,” and we couldn’t agree less. If you want a unit that will not disappoint, then you should consider the Rinnai RUC99iN Sensi Water Heater.

Currently one of Rinnai’s best sellers, the Rinnai RUC99iN is one of the best tankless models currently available in the market. Don’t worry;you will soon discover why.

Top on the list of the major highlightsof the heater is its ThermaCirc360 technology, which features a recirculation pump that ensures a rapid supply of hot water.

This helps to greatly minimize water wastage, especially when compared to a traditional tank option.

The heater has a UEF (Uniform Energy Factor) of 0.92, which is quite impressive. This ensures less gas is used by the unit for the heating process. The unit also has a heat output between 15,000 BTU to 199,000 BTU.

You will also save considerable space by installing the heater as it has a very compact design. Gone are the days where you have to install a behemoth for a water heater.

Today’s heaters (especially tankless models) are much more space-saving.
With the Rinnai RU199iN, installation is also flexible as you can opt for either concentric or PVC venting.

Overall, this is a great heater with a load of useful features. We highly recommend it!


  • Fast heating
  • Energy saving
  • Occupies less space
  • Remote control included
  • High water flow (up to 11 GPM)
  • Quiet operation


  • Expensive

6) Rinnai RL94iN HE+ Tankless Hot Water Heater

The Rinnai RL94iN is another premium tankless heater that is suitable for both domestic and commercial use.

Like the previous unit we reviewed, this one is a natural gas model (the propane version is also available); so it supports the indoor installation.

As expected, the heater has a considerably high flow capacity, which makes it a great choice for big homes.

Flow rate can reach up to 9.4 GPM, which is enough to support up to five bathrooms as well as appliances like your washing machine and dishwasher.

Like the Rinnai RUC99iN, it is also outfitted with a recirculation technology (Circ-Logic), which allows you to set the unit to monitor your consumption and then redistributes supply according to your family needs.

The heater boosts of high thermal efficiency (around 0.83) and a BTU factor ranging from 10,300 to 199,000.

In addition to its recirculation technology, the unit also comes with Wi-Fi monitoring, which allows you to monitor its efficiency and performance conveniently.

This way, you can identify and resolve issues before they escalate and disrupt service.
We are also impressed with the compact design of the heater, low gas emission, and less energy usage.With a little bit of plumbing knowledge, you should find the installation fairly easy.

In the end, what you get is a highly efficient water heater that is powerful and fast. The huge number of positive reviews online easily confirms this.


  • High flow rate
  • Space-saving
  • Dual installation options
  • Wi-Fi monitoring
  • Energy-efficient design


  • Venting kit not included

7) StiebelEltronTempra 24 Plus Tankless Water Heater

Besides their energy efficiency, another reason a lot of people opt for tankless water heaters is thatthey don’t make much noise.

The Tempra Plus by StiebelEltron is one of the best options you will find in this category.

So what is responsible for its quietness? There were two things we found to be behind this.

Firstly, the heater is made up of high-grade components that do not vibrate. This also applies to the cover.Secondly, there’s not one mechanical switch on the unit.

You will also be glad to know that the heater is outfitted with an Advanced Flow Control Technology, which helps it to maintain a constant temperature even when you tweak the flow rate.

Many tankless heaters are usually unable topreserve the water temperature, especially at higher flowrates; thus the water hotness decreases as you raise the output leasing to an uneasy experience.

Luckily, with the Tempra Plus, you don’t have to worry about this. It has a flow rate of 4GPM and comes with a very compact design and thus requires less space for installation.

The heater also features True Thermostatic Temperature, which automatically adjusts power to meet the heating demands.

This, together with its self-modulating technology, helps to enhance the efficiency of the unit.

Overall, we consider this heater a great bargain for its price given what it brings to the table. We have no doubt you will come to appreciate it.


  • Intuitive temperature display
  • Sleek design (space-saving)
  • Quality construction
  • Digital controls
  • Temperature sensor for uniform temperature regulation


  • Expensive

8) EcoSmart ECO 27 Electric Tankless Water Heater

For the best smart electric tankless water heater, we couldn’t find any better option than the EcoSmart ECO 27.

Our reason for choosing the ECO 27 is not because it’s coming from one of the most reputable brands in the industry. Rather, it’s the features it offers that put it at thetop of the pyramid.

This is quite evident in the huge number of rave reviews the product has garnered so far from different categories of users.

The heater proves to be highly energy-efficient and works best for light domestic applications.

In other words, if you live alone or with just one person, you will find its 3 GPM flow rate quite sufficient to meet your hot water needs. It is an also a great choice for average-sized homes without huge hot water demand.

Like most high-end units, the heater is outfitted with premium features like temperature control and self-modulating technology. This helps to improve the efficiency of the unit greatly.

The unit also features copper and stainless steel parts, which ensure high thermal efficiency and durability.

Overall, this is a great heater to invest in if you want a unit that will not disappoint. We have no doubt you will get good value for your money.


  • Low maintenance
  • Highly durable
  • Digital temperature control
  • Self-modulating technology
  • Compact sizing


  • Not energy star certified

9) Ecosmart ECO 18 Electric Tankless Water Heater

To round off the list is another amazing product from Ecosmart – the ECO 18. While this is not the most advancedunitfrom the company, it arguably provides the best combination of price and power.

With the ECO 18, you get up to 2.5 GPM, which easily translates to a single shower head and a sink.

It is also capable of supporting two showers simultaneously provided the temperature of the incoming water is more than 70 degrees.

Just like the ECO 27, this unit is made of copper and stainless components, which make it highly durable.

It is also outfitted with digital control that gives you complete control over temperature, allowing you to adjust it by increments of 1 degree.

Temperature ranges between 80 – 140 degrees Fahrenheit, which should be adequate for any household.

By properly sizing the unit, Ecosmart is able to ensure you get an endless supply of hot water while using only the energy that is required.

In the end, what you have is a highly effective tankless water heater that considerably cuts down your energy bills.


  • Small and lightweight
  • Budget-friendly
  • Better for the environment
  • Self-modulating
  • Adjustable temperature control
  • Easy to install


  • Temperature fluctuations at higher household demands

Tankless Water Heater or Indirect?

Now, let’s get into the specifics and see how both types of heater compare with each other:

Tank Requirement

This primary difference between both types of the heater is obviously the presence of a water tank. While an indirect heater comes with a tank, a tankless model doesn’t need one.

Power Source

Indirect water heaters can be powered by electricity, gas, solar, or a combination of these. However, tankless heaters usually run off on either gas (propane or natural gas) or electricity.

Energy Efficiency

When it comes to energy efficiency, both indirect heaters and tankless systems are almost equivalent.

However, indirect systems still have the upper hand. This is because an indirect heater relies on the efficiency of your boiler, and boilers generally do better than most water heaters.

Some modern boilers can achieve up to 96 percent efficiency while, in practice, the best tankless models offer around 90 percent efficiency(80 is more common).

On-Demand Water

Both tankless and indirect heating systems work intermittently to provide water in an on-demand way.

Maintenance and Lifespan

Both indirect and tankless systems require less maintenance. However, indirect systems are much easier as they have fewer parts.

Both types of heaters also have a similar lifespan — usually between 8 – 20 years depending on the model and the level of maintenance.

Size and Installationv

In terms of size, it seems both heaters scores the same mark asthey are generally compact in size. However, installation is a bit more complex with indirect heaters.

Flow Rate

Tankless heaters usually have a specific flow rate (i.e. gallons per minute), and this is what they always produce under the right conditions.

However, with an indirect unit, the water output is only limited by the size of the tank.

Final Verdict

There you have it – our indirect water heater vs. tankless heater comparison.
Whether your existing heater has outstayed its useful life or you wish to upgrade to a better performing unit, you cannot go wrong with either a tankless or indirect water heater.

It is obvious both types of heaters are highly efficient and durable. Choosing between both models boils down to your individual family needs.

However, we recommend an indirect heater if you have a large or busy home, but for lighter applications such as a small residence, a tankless model might be a better option.

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