How does an indirect water heater work?


Mod­ern man can no longer imag­ine life with­out hot water. More­over, not only at home, but even in the coun­try. In the absence of a cen­tral sup­ply, many decide to install a boil­er to heat water. The indi­rect tem­per­a­ture increase mod­el is con­sid­ered to be the most pop­u­lar recent­ly. It is one of the most unpre­ten­tious and at the same time eco­nom­i­cal.

What’s this?

There are two types of sim­i­lar tools that are sim­i­lar to each oth­er: a direct and indi­rect heat­ing boil­er. The sec­ond option is a liq­uid heater that uses the heat of the heat­ing sys­tem.

The main dif­fer­ence from anoth­er type is that the unit rais­es the tem­per­a­ture of the water not through elec­tric­i­ty, but through cen­tral heat­ing or a boil­er.

Most often, a bar­rel is used as an out­er cas­ing. At the same time, cubic instal­la­tions have become more pop­u­lar recent­ly. They are made in the style of the main boil­er and are often installed direct­ly below it, there­by sav­ing space in the room.

How does the system work?

Many have heard, but do not know how an indi­rect heat­ing boil­er works. The prin­ci­ple is sim­ple. There is an inner tank which is made of stain­less steel or even plas­tic. From above it is cov­ered with a spe­cial heat-insu­lat­ing mate­r­i­al. Inside, a met­al heat exchang­er (usu­al­ly made of brass) is most often installed. It is through it that the liq­uid from the boil­er is launched. To ensure fast heat­ing, it is made in the form of a spi­ral coil.
The case is cre­at­ed in the style of oth­er mod­els of the man­u­fac­tur­er.

A mag­ne­sium anode is built in to pro­tect against cor­ro­sion. To pro­tect the sys­tem from high pres­sure, a ther­mo­stat and a spe­cial valve are used.

There are also options on the mar­ket that have a dif­fer­ent indi­rect heat­ing boil­er device. So, for exam­ple, it can be a “tank in a tank”, and the coolant is let in between the walls. In addi­tion, sev­er­al com­po­nents are used at once for heat exchange. Sim­i­lar designs are found on the mar­ket much less often than the main ver­sion.

To fill the tank, cold water is con­nect­ed. Also in the tank there is an out­let for hot. Cold water enters the heater, and at the out­let the con­sumer receives already hot. Each such boil­er is con­nect­ed to a pipeline through which the coolant pass­es through the tank and the boil­er. Such a sys­tem nec­es­sar­i­ly has a pump to cre­ate forced pres­sure in order to cir­cu­late the liq­uid.


This sys­tem has many advan­tages:

  1. The oper­a­tion of the water heater can­not over­load the elec­tri­cal cir­cuits in the room, as it is com­plete­ly depen­dent on heat­ing and does not con­sume ener­gy.
  2. Suc­cess­ful mod­els have a high effi­cien­cy and an opti­mal ratio of the con­sum­ables.
  3. The coolant does not inter­act direct­ly with run­ning water. This allows you to sig­nif­i­cant­ly increase the ser­vice life of the unit.
  4. The device of the boil­er for heat­ing water allows you to imme­di­ate­ly sup­ply hot water — there is no need to pre-drain.
  5. The unit can always be con­nect­ed to an alter­na­tive heat source.
  6. It is pos­si­ble to use sev­er­al heat­ing ele­ments.


Despite all the advan­tages, this design also has a num­ber of dis­ad­van­tages:

  1. The ini­tial cost of such a boil­er is high­er than elec­tric or gas.
  2. The first heat­ing of a tank of 100 liters is car­ried out in 1–2 hours, which imme­di­ate­ly affects the heat­ing.
  3. In most cas­es, such sys­tems need to be installed in sep­a­rate rooms.

What to look for before buying?

The first thing to con­sid­er is vol­ume. It is impor­tant to under­stand how much water will be con­sumed and at what fre­quen­cy for the com­fort­able exis­tence of the whole fam­i­ly. There are aver­ages. So, about 5–15 liters are spent per day per per­son on per­son­al hygiene, 15–25 liters on dish­es, 50–100 liters for a show­er, and 150–200 for a bath.

On aver­age, one indi­vid­ual accounts for about 100 liters of water per day. Of course, it all depends on the pref­er­ences and habits of the per­son him­self. Some­one takes a show­er twice a day, and some­one is enough and one.

It must be remem­bered that the larg­er the vol­ume, the high­er the price of the device.

Anoth­er impor­tant detail in such a water heater is the mate­r­i­al from which the inner part is made.

For exam­ple, it is bet­ter to choose instal­la­tions whose coil is made of brass. The fact is that this met­al has a high­er heat con­duc­tiv­i­ty than the same steel. In addi­tion, it is much eas­i­er to clean such ele­ments.

The con­tain­er itself must be pro­tect­ed against cor­ro­sion. Cheap options are enam­eled or glass-ceram­ic. Expen­sive mod­els are made of stain­less steel.

You also need to remem­ber about the ther­mal insu­la­tion of the entire con­tain­er. For qual­i­ty mod­els, this is polyurethane foam or min­er­al wool. But it is bet­ter to imme­di­ate­ly reject options with foam rub­ber.

Connecting to the system

There are two options accord­ing to which this hot water boil­er can be con­nect­ed — hydraulic and elec­tric method. The first scheme is con­sid­ered more effec­tive.

So, two pumps are used at once. The action of one is aimed at heat­ing the room, and the sec­ond — to inter­act with the boil­er. In turn, the elec­tri­cal con­nec­tion implies auto­mat­ic switch­ing using a relay.

The two-pump method con­sists in the move­ment of flows in dif­fer­ent direc­tions. Each indi­vid­ual hot water line is con­nect­ed in par­al­lel. In this case, the oper­at­ing mode of the pumps them­selves is reg­u­lat­ed by a tem­per­a­ture sen­sor. After each device for cre­at­ing arti­fi­cial pres­sure, a check valve is installed — this allows them to work indi­vid­u­al­ly.

Errors during connection

There are sev­er­al major mis­takes that peo­ple most often make when buy­ing such units. So, first­ly, many peo­ple choose a place that is not quite suit­able for instal­la­tion, since the prin­ci­ple of oper­a­tion of the boil­er direct­ly depends on the dis­tance to the boil­er or the cen­tral heat­ing out­let.

In addi­tion, it is often pos­si­ble to find incor­rect con­nec­tions to the cold water pipe. It must be con­nect­ed to the bot­tom of the unit.

It is also impor­tant to main­tain a series con­nec­tion of the inlet and out­let of the coolant, which is the key to effi­cient oper­a­tion. Opti­mal per­for­mance can be achieved only when the heat­ing liq­uid enters the heater from above.

One of the most impor­tant points is the con­nec­tion of the pump, because its incor­rect instal­la­tion entails sev­er­al seri­ous unpleas­ant con­se­quences at once. So, the axis should be in a hor­i­zon­tal plane, which will pre­vent rapid wear of the bear­ings. It is also impor­tant to con­stant­ly mon­i­tor the strain­ers that pro­tect the pump from debris.

A water heater with an indi­rect sys­tem is today con­sid­ered one of the most eco­nom­i­cal of these units that are used in rooms of any type. They come in dif­fer­ent designs and vol­umes, which allows you to choose the best option.


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