Best Indirect Water Heaters of 2021 – Complete Buyer’s Guide

| Last Updated: June 30, 2021

If you want an efficient and energy-saving water heater but for a bigger home, then a tankless water heater will not do the job. For this purpose, indirect water heaters are used.

This article lists the best indirect water heaters available and how they work to help you decide if they are the right choice for you.

Comparison Chart of the Best Indirect Water Heaters

  • Has a capacity of 35 gallons
  • Comes with an optional limited lifetime warranty
  • Best for the money
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  • 316L stainless steel building material
  • Has a 150psi working pressure
  • Best Lochinvar indirect water heater
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  • Supports 35, 50, 80, 119 Gallon capacities
  • SuperStor contender Flow coat technology
  • Best HTP indirect water heater
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What Is an Indirect Water Heater?

An indirect water heater is an energy-efficient and low-cost water heater. They have a water tank, unlike the tankless water heaters and a furnace or boiler to heat the water. They use the home’s already installed space heating system and can be used with oil, gas, electricity, solar energy, propane, or a combination of these.

They store enough water to supply the entire house and have a good heating rate. You don’t need to burn the furnace for too long and too often. Indirect water heaters can work in both cold and warm climate areas.

How Does an Indirect Water Heater Work?

A lot of modern homes have space heaters installed in them. An indirect water heater makes use of that system and heats its water through the space heating furnace. That heat is then circulated through the heat exchange coil in the water heater.

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The ability of the water heater to store energy and use an already working furnace for heat makes it an efficient energy-saving model. The tank itself needs no power to work; it simply uses the heat exchange mechanism.    

How to Choose an Indirect Water Heater

Some things to look for in a good indirect water heater are:


When most people think about energy-efficient water heaters, they think about tankless water heaters. They don’t store water, and they don’t need to be running all the time. You can get instant hot water with them. The main reason people choose to buy the indirect heater instead is that it can give hot water for long periods and for more use. This is why it is important to see that the capacity of the tank meets your requirements. 


Since the tank itself has no power and uses an external source, it should be able to retain the heat once that source is turned off. Otherwise, the water will get cold, and you will have to keep the furnace or boiler running for longer. A good indirect water heater has a highly insulated tank to achieve this.


Indirect water heaters don’t work with forced-air furnaces. They can only be heated by furnaces that work with integrated HVAC (heating, ventilation, air conditioning) systems. These cannot be found in older homes. If you live in an older style home or a home that does not require large water storage, you might want to consider another option. 

Review of the Best Indirect Water Heaters 

To make sure that you quickly and easily find your desired unit, we’ve reviewed some of our top picks in detail. 

Best Overall

Burnham AL35SL

Burnham AL35SL Alliance SL Hydrastone-Lined Indirect-Fired Water Heater, 35 gal


Capacity (Gallons): 35

First Hour Rating: 200 GPH at 135°F

Working Pressure: 150 psi

Dimensions: 22.75 x 39.25″

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What Recent Buyers Report

The product is in good shape, as per the customer reviews. It gives a fairly good performance. The capacity is great for an average home. You get hot water all day. It works with different power supplies. Users also state that you save a lot of money and energy with this model.

Why it Stands Out to Us

This water heater is a space-saving and cost-saving alternative. You get good heat insulation capacity with its high-density insulation. It is highly durable and corrosion-resistant. The heat loss is extremely low. It uses a hydra stone lining, which is harder than plaster of Paris.  

Who Will Use This Most

This is a budget-friendly water heater. You can install it in a small space, and if there is little to average water usage in the house, this will work perfectly. It can give hot water continuously for a small family. 

Bottom Line

Traditional water heaters can be expensive. Indirect water heaters come not only as an energy-saving but also as a cost-saving alternative. This model is even cheaper than its competitors. You get high-quality and good hot water at a low price.


A high capacity heating coil

Less than 1-degree loss of heat per hour

Has a corrosion-resistant hydra stone lining

Up to 30% savings over conventional water heater

High-density R-16 insulation for better heat retention


It is a fairly older model

Best Lochinvar Indirect Water Heater

IPW015DW Commercial Water Heater


Capacity (Gallons): N/A

Flow Rate (GPM): 8.5 at 145°F

Working Pressure: 150 psi

Dimensions: 44 x 10.5 x 55″

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What Recent Buyers Report

This water heater is used by people that don’t need a lot of water storage. It gives instant hot water. There is no need to wait for it to heat up. The size is pretty small, and it is easy to install too. The temperature setting is also easy with digital control. You get a high-quality product at a good price. It also saves a lot of energy.

Why it Stands Out to Us

This water heater gives advanced temperature control. It has a digital display, a modulating control valve, and a temperature sensor. It is made from highly durable stainless steel. The air valve is automatic, which makes it safer. You get continuous hot water with this indirect heater.

Who Will Use This Most

This water heater does not have a tank, which means it is made for hot water systems for continuous loading. It gives on-demand hot water every time without having to store it. It works with a boiler and is used in homes with little space. Since it doesn’t have a tank, the installation will hardly take any space. 

Bottom Line

Lochinvar provides a range of commercial, residential, and tankless water heaters along with boilers and tanks. You can choose from a number of condensing and non-condensing heaters. This indirect heater is a tankless kind of heater. It takes up minimum space in your house and gives hot water instantly whenever needed.


Has an automatic air vent

Has a scale reduction pump

Double-walled plate and frame

Temperature sensor and control valve

Electronic temperature control and display


No water storage tank

Best HTP Indirect Water Heater

SuperStor Contender Water Heater


Capacity (Gallons): 35 – 119

First Hour Rating: 112 – 268 GPH at 140°F

Working Pressure: 150 psi

Dimensions: 23 x 36.25″ – 28 x 67″

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What Recent Buyers Report

This water heater is great for different homes. The differently sized units all have good performance and give hot water continuously. The variable capacities are great. It is made from highly durable and resistant material. The insulation is also good, and it does not need the furnace to burn too long. It can save a lot of energy and money.

Why it Stands Out to Us

This water heater has an eco-friendly 2-inch insulation material that can retain heat for a long time. The tank and coil are corrosion-resistant. It uses a flow coat enamel heat exchanger for better thermal conductivity. It also has a factory-supplied full port drain and T&P valve.

Who Will Use This Most

This water heater model has four different sizes. The 30 and 50-gallon variants serve a lot of people and can be used in average-sized homes. They give 113 GPH and 190 GPH, respectively, at 140F. The 80 and 119 Gallon water heaters can be used for small business buildings or larger homes with a lot of people. They have 1198 and 268 /gph, respectively, at 140F.

Bottom Line

This is HTP’s best indirect water heater. It is environment-friendly and energy-efficient. It comes in sizes for all homes. It is extremely durable and corrosion-resistant. Its installation is easy since the company provides an installation manual. And you get a 7-year limited residential warranty too.


Ceramic-coated smooth surface coil

Oversized anode rod for corrosion resistance

This model has many different sizes for every house

Environmentally friendly water-blown foam insulation

Various gallon capacities make it suitable for different applications


Product Warranty is comparatively low

Best 30 Gallon Water Heater

BIC IBC Indirect Water Heater- IBC30

BIC IBC Indirect Water Heaters- IBC30, 30 Gallon Storage, 150psi.


Capacity (Gallons): 30

First Hour Rating: 159 GPH at 135°F

Working Pressure: 150 psi

Dimensions: 20 x 39.6″

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What Recent Buyers Report

As per customer reports, this water heater has great heat capacity. It is perfect for small homes. It saves a lot of money and is a greener product. Its quality is great, and it’s very durable. Users also find the lifetime warranty to be a plus.   

Why it Stands Out to Us

This water heater is made up of 316L stainless steel material that gives it high durability and strength. Its installation is pretty easy, with connections provided on the top. The size is small to save space. It has high capacity and smooth-walled coils. The 2-inch insulation and thermoplastic jacket makes its heat retention capability high.  

Who Will Use This Most

This indirect water heater is for smaller homes that have fewer needs and people that want to save space. The 30 Gallon option is perfect for the average home. But the company provides similar water heaters in larger capacities like 40,50,60,80, and 115 gallons if needed. The bigger models are adjusted to meet the needs of large water heating.

Bottom Line

For a 30 Gallon water heater, this is one of the best options. It is made of high quality durable material. Its maximum first-hour rating is 176 Gallon/h at 140F. Then a 149 Gallon/h continuous rating. This heater has a lifetime warranty as well, so it will probably work for a long time.


Stainless steel build for durability

Energy Star qualified water heater

2-inch wall to better heat retention

Fail-proof welded stainless steel dip tube

Thermoplastic jacket for corrosion prevention


Only for small homes 

Best 40 Gallon Water Heater

BIC IBC Indirect Water Heaters- IBC40

BIC IBC Indirect Water Heaters- IBC40, 40 Gallon Storage, 150psi.


Capacity (Gallons): 40

First Hour Rating: 188 GPH at 135°F

Working Pressure: 150 psi

Dimensions: 21.4 x 47″

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What Recent Buyers Report

This product has a good capacity for average homes. It gives a continuous supply of hot water. Its build quality is great and does not damage easily. You can use it all day and for years without any need for replacing. The maintenance is pretty low, as stated by consumers. It is very easy to install and use too.

Why it Stands Out to Us

This water heater is manufactured by a trusted manufacturer, BIC. It has similar characteristics as the model reviews above but with a bigger size. Its maximum first-hour rating is 193 gallons/h at 140F, which goes to 157 gallons per hour for continuous rating. It has a high heat retention capacity and comes with a temperature sensor to manage the water heater.  

Who Will Use This Most

This model is for slightly bigger homes since it has more capacity. It can still not be used for extremely large homes and big buildings. For a normal, medium-sized family, it works fine. Plus, it complies with U.S. building and energy standards.

Bottom Line

IBC boilers produce a vast range of quality products. This water heater from their line of indirect water heater has high insulation and good quality. You can monitor the temperature with its temperature sensor. There is also an optional Honeywell aquastat feature for controlling boiler on/off timings.


Has an optional lifetime warranty

High capacity coils that prevent airlocks

Full 2-inch insulation for low standby loss

High grade durable stainless steel material

10k ohm temperature sensor that works with VFC and SL condensing boilers


Doesn’t cater to larger homes

Pros and Cons of Indirect Water Heaters

While indirect water heaters have their advantages, they don’t come without limitations. Thus, it’s better to know both sides of the story before deciding to make a purchase.


Some of the benefits of indirect water heaters are:

Less Maintenance

Indirect water heaters have fewer mechanical parts because they don’t have an internal heating system. This results in less maintenance.

Less Money

They cost way less than traditional water heaters. And because they use an already-installed heating furnace or boiler, you don’t need to spend extra money on its fuel.

Less Space

They are much smaller in size than an average traditional water heater. Therefore, you don’t need a dedicated space for their installation. 

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Better Insulation

These water heaters always have high-quality insulation to make sure the heat does not get lost too rapidly.  

Less Energy

Since you will be using the heating system that is already running to heat your home, you don’t need extra power. This ends up reducing the amount of fuel used.


Everything has its downfalls. Some cons of these units include:

A Furnace Is Necessary

This water heater system needs a furnace that works with the home heating system. That is not available in older homes. If that is the case, then you will need to install it, and that will end up costing you more. 

Not Ideal for Smaller Homes 

If you have a small home or just one or two people using the hot water, this will be a waste of space and energy. Since it will store more water than is needed, you will end up making an energy-efficient product not so efficient.


Indirect water heaters are confused with tankless water heaters. This article hopefully cleared that confusion. They are great for domestic use, where space-saving and cost-saving are essential. All these products are of top quality and will give hot water at good rates.

People Also Ask

If you still have some questions about indirect water heating, then you are not alone. A lot of people confuse it with other types of heating. For answers to your questions, you can read these frequently asked questions.

How Long Does an Indirect Water Heater Last?

These tanks last for a much longer time than traditional water heaters. Some manufacturers even provide lifetime warranties for their products. They are made from stainless steel and don’t get direct heat, so they are not damaged easily. Traditional water heaters have an average lifespan of about 1o to 15 years. But with an indirect water heater, you will get much more.

What Is the Difference Between Direct and Indirect Water Heaters?

Indirect water heaters use a separate furnace or boiler to heat the water. They have no internal heating mechanism other than the heat exchange coil that uses the heat from the external burner to increase the water temperature. Direct water heaters have an inbuilt boiler to heat the water. They are much larger and have more parts.

Do Indirect Water Heaters Have Anode Rods?

Yes, indirect water heaters have an anode rod as well. Every water heater needs an anode rod. It is one of the vital components. Anode rod is used to prevent rust on the water heater. Rust is especially a problem in saltwater.

A good anode rod can increase the water heater lifespan significantly. If your anode rod is not working properly or is damaged, then you will notice considerable rust on the inside of the tank. This will reduce the water flow and heating capacity. And you will end up having to do maintenance more often or will have to change the water heater sooner than most.

My name is Bob Wells and I am a retired HVAC tech from Washington state. I am currently retired and no longer do much with HVAC, however, I feel like I have a lot of knowledge in the subject and I wanted to create a website where I could talk about what I've learned and help upcoming HVAC techs. Find more info about me and HVAC Training 101.