If there is one thought that can really cause discomfort during cold winter months, it’s that of running out of hot water! That’s why an indirect water heater is so reliable. Indirect water heating systems are one of the cheapest methods of producing hot water for domestic use. They use a system that’s based on indirect firing of the furnace or the boiled for producing heat that heats up the water. Since water inside the insulated tank is not heated directly by the energy produced inside the furnace, this system is known as indirect water heating system.

Due to the insulated storage tank, the heat inside the tank can’t escape easily and less fuel is used leading to lower utility bills. An indirect water heater can be easily used 365 days of the year and once have it installed in your home; you’ll never have to worry about running out of hot water ever! Best of all, since the indirect system is integrated into a home’s heating system; it can heat water even when there is no need for central heating.

Indirect water heater can produce hot water using different and commonly available fuels like electricity, oil, propane, natural gas and solar energy. Many people also use heat pumps and gas/oil burning furnaces as a source of energy for heating water.

Types Of Indirect Water Heaters

Broadly speaking there are four types of indirect water heaters and they are:

1.    Internal coiled type
2.    External submerged type and
3.    Furnace-based type
4.    Tank-in-tank type

Internal coil indirect water heater: It’s the most commonly used indirect water heating system and has a coil placed inside the storage tank that allows for heating of a large quantity of water with amazing recovery rates.

External submerged indirect water heater: Consists of copper tubes that are protected by a stainless steel or cast iron shell. There is a need for an external heat exchanger that used one pump each for water and heat transfers.

NOTE: You can also construct an indirect water heater with three main parts – a storage water tank, furnace or boiler for combustion and heater controls.

Furnace based indirect hot water heater: This is the least common type of indirect water heater. In this system the heat exchanger coil circulated water through the boiler/furnace so that it can be heat and then it is sent to a storage tank for use.

Tank-in-tank type of indirect water heater: This type of an indirect-fired water heater is made of two tanks; the inside tank is made from corrugated SS while the outer tank is made from SS. The Weil Mclain indirect water heaters are good examples of tank-in-tank heaters.

A highly effective water heating system, this design is 3-times more capable than an electric water heater, and 2-times more capable than a tankless coil water heater.

Indirect-fired hot water heating systems are also known as “combined systems,” as they use a combined heat source for heating water and space inside a home.

NOTE: Indirect water heaters have an efficiency rating between 0.59 and 0.90. It’s best to buy a water heater with an EER of 0.85 or higher.

Advantages Indirect Water Heaters

1.    Gas-fueled indirect water heaters have a significantly lower loss of heat through the flue.
2.    As compared with to traditional tank-type water heaters, an indirect water heater is a lot more energy efficient with hardly any standby heat loss.
3.    The maintenance level is very low because there are no additional burners or pilot lights.
4.    Low cost of purchase and installation since no extra venting or fuel pipes need to be added.
5.    Compact size and easy installation.
6.    Gives excellent performance and more hot water with quick-paced recovery because BTU output source is the boiler/furnace.
7.    Reduction in backdrafting and reduced service charges as a single venting system is used.
8.    Have an increased life span since thermal stress is very low due to indirect heating.
9.    Many indirect water heaters come with a lifetime warranty.

NOTE: When buying an indirect water heater check the recovery rate as well as the capacity for enhanced performance.

Manufacturers Of Indirect Water Heaters

There are many different indirect water heater manufacturers and they are:

1.   Coliex – offers large amount of hot water, stainless steel tanks, and high efficiency with low standby heat loss. Sturdy built can withstand accident/damage.
2.    Amtrol – a wide range of indirect water heater systems with available in various budgets.
3.    Heat Wave – offers high quality indirect water heaters for most uses like residential, commercial, restaurants, and even schools.

Then there are others like Crown Mega-Stor, and Bock SideKick, among others.

Top 2 Indirect Water Heater Models

Crown Mega-Stor Indirect Water Heater


1.    Domestic water heater
2.    Fuel types – Oil or gas
3.    Five sizes with round vertical tank with capacities from 26 to 112 gallons
4.    Two sizes in rectangular horizontal tank with capacities from 38 to 51 gallons
5.    Provides large quantities of hot water
6.    Tank made from 316 grade SS with SS coil
7.    Removable inspection cap for checking level of water and coil on both types of tanks
8.    2” polystyrene foam insulation for decreasing standby heat loss
9.    High impact plastic jacket
10.    Lifetime warranty for leakage on tank and coil
11.    First hour delivery from 103 – 417 gallons depending on model
12.    90-degree rise based on size of heater and boiler used
13.    Round tank models available: MS-26 (26g); MS-40 (39g); MS-53 (51g); MS-79 (80g) and MS-119 (112g)
14.    Rectangular tank models available: MSH-40H (38g) and MSH-53H (51g)

Bock SideKick Indirect Water Heater


1.    Domestic water heater
2.    Fuel types – Oil or gas
3.    Five sizes ranging from 30g to 110 gallons
4.    Provides large quantities of hot water
5.    Tank made from 316 grade SS with SS coil
6.    First hour delivery from 115 gallons to 346 gallons depending on the model
7.    77-degree rise based on side of heater and boiler used
8.    High reputation for durable and long lasting operation
9.    12 gauge thick SS tank construction
10.    1 ½” diameter indirect heating coil for higher rate of heat transfer
11.    C-glass (cobalt enriched porcelain enamel glass) coating on tank and coil
12.    2” non-CFC foam insulation for decreasing standby heat loss
13.    High impact powder coasted steel jacket
14.    Lifetime warranty for residential indirect water heater
15.    3-year warranty for commercial indirect water heater

Models available: 30SK (30g); 40SK (38g); 50SK (45g); 8OSK (75g) and 119SK (110g)

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