We understand the heating scheme from a solid fuel boiler


Cur­rent­ly, more and more own­ers of pri­vate hous­es, cot­tages are try­ing to achieve inde­pen­dence from sources of cen­tral ener­gy sup­ply. If with elec­tric­i­ty this issue is not rel­e­vant and prob­lem­at­ic due to tech­ni­cal com­plex­i­ty, then with the heat­ing of res­i­den­tial build­ings the sit­u­a­tion is much sim­pler. Autonomous gas heat­ing is pop­u­lar among res­i­dents of the pri­vate sec­tor, how­ev­er, in those con­di­tions where there is no cen­tral­ized gas sup­ply, sol­id fuel boil­ers come to the fore.

Heat­ing devices of this type are expe­ri­enc­ing a rebirth today. Stoves and fire­places famil­iar to all of us, used in the old days for heat­ing res­i­den­tial build­ings, are now giv­ing way to high-tech boil­er equip­ment.

The scheme of a heat­ing boil­er, the device of a sol­id fuel boil­er in its cur­rent form allow us to under­stand not only the prin­ci­ple of oper­a­tion of heat­ing devices of this type, but also to appre­ci­ate the enor­mous pos­si­bil­i­ties of such equip­ment. The prin­ci­ple of oper­a­tion of sol­id fuel boil­ers is in many ways a key aspect that the con­sumer pays atten­tion to today. In order to use the autonomous heat­ing sys­tem with max­i­mum ben­e­fit, you should under­stand two points:

  • what ele­ments and parts does a sol­id fuel boil­er con­sist of;
  • what is the basic scheme of oper­a­tion of a sol­id fuel boil­er.

See also: the prin­ci­ple of oper­a­tion of a gas boil­er.

Operation of solid fuel boilers. New opportunities

Unlike gas and elec­tric heat­ing, using a home heat­ing sys­tem with a sol­id fuel boil­er requires great phys­i­cal effort and appro­pri­ate tech­ni­cal train­ing from home­own­ers. Hav­ing sig­nif­i­cant tech­ni­cal and domes­tic lim­i­ta­tions, sol­id fuel boil­ers have one indis­putable advan­tage in com­par­i­son with gas heaters, not to men­tion elec­tric­i­ty. A sol­id fuel heat­ing boil­er is 80–90% ener­gy-inde­pen­dent device. A suf­fi­cient sup­ply of fos­sil fuels, fire­wood or pel­lets will allow you to not only heat your own house calm­ly all win­ter, but also pro­vide your­self with hot water.

The heat­ing sys­tem con­nect­ed to a sol­id fuel boil­er does not depend much on pow­er out­ages. She is not afraid of drops in work­ing pres­sure in the gas line. The cost of fuel and the avail­abil­i­ty of free access to it will ensure the nor­mal and unin­ter­rupt­ed oper­a­tion of all heat­ing equip­ment in the house. Man­age­ment of sol­id fuel boil­ers allows you to oper­ate the units in any oper­at­ing mode, there­by ensur­ing the safe­ty and com­fort of the inhab­i­tants of a res­i­den­tial build­ing.

Domes­tic man­u­fac­tur­ers, for­eign com­pa­nies spe­cial­iz­ing in the pro­duc­tion of boil­er equip­ment today offer the con­sumer a qual­i­ta­tive­ly new prod­uct. Sol­id fuel boil­ers that are used for domes­tic and indus­tri­al pur­pos­es have a high­er effi­cien­cy. Today this para­me­ter reach­es 90%.

For ref­er­ence: old sol­id fuel boil­ers in the tra­di­tion­al design had an effi­cien­cy of 70–80%. The low ener­gy effi­cien­cy of old-gen­er­a­tion heat­ing equip­ment led to sig­nif­i­cant fuel over­runs and sig­nif­i­cant loss­es of ther­mal ener­gy.


Design inno­va­tions and “know-how” in the field of prac­ti­cal appli­ca­tion of var­i­ous ener­gy resources have made it pos­si­ble to sig­nif­i­cant­ly expand the oper­a­tional capa­bil­i­ties of heat­ing equip­ment. Huge pow­er is one of the main advan­tages of sol­id fuel boil­ers. The prof­itabil­i­ty of mod­ern mod­els of sol­id fuel boil­ers has increased by an order of mag­ni­tude. The safe­ty of oper­a­tion of this type of boil­er equip­ment has sig­nif­i­cant­ly increased.

A dou­ble-cir­cuit sol­id fuel boil­er is able to pro­vide heat­ing for large and spa­cious rooms. In addi­tion, almost all mod­els of boil­ers are designed to pro­vide domes­tic hot water facil­i­ties.

Design features of solid fuel boilers

A tra­di­tion­al sol­id fuel boil­er is, in our under­stand­ing, a heat­ing unit capa­ble of oper­at­ing on any sol­id fuel. The prin­ci­ple of oper­a­tion of the boil­er is ele­men­tary. The fuel enter­ing the com­bus­tion cham­ber dur­ing the com­bus­tion process releas­es a large amount of ther­mal ener­gy, which heats the coolant. Accord­ing to a sim­i­lar prin­ci­ple, stove heat­ing was orga­nized in the old days, only hot air was used instead of a liq­uid heat car­ri­er.

A sig­nif­i­cant dis­ad­van­tage of the tra­di­tion­al mod­el of a sol­id fuel boil­er is that part of the heat gen­er­at­ed by the com­bus­tion of fuel sim­ply escapes into the atmos­phere through the chim­ney. Con­sid­er a schemat­ic dia­gram of a sol­id fuel boil­er. The boil­er device is a struc­ture assem­bled from var­i­ous mod­ules into a sin­gle steel case. The main struc­tur­al ele­ments of this type of heat­ing equip­ment are:

  • com­bus­tion cham­ber (fur­nace equipped with a door);
  • heat exchang­er (steel or cast iron);
  • clean­ing hatch;
  • grate (lat­tice);
  • ther­mostats;
  • safe­ty valve.

The tra­di­tion­al sol­id fuel boil­er of the new gen­er­a­tion shown in the fig­ure is equipped with all the devices, mech­a­nisms and ele­ments nec­es­sary for nor­mal oper­a­tion.

The combustion chamber — the processes occurring in it

One of the first ele­ments that you have to get acquaint­ed with first of all is the boil­er fur­nace. It is the ships that lay coal, peat, bri­quettes or fire­wood, and it is here that the main process takes place — fuel com­bus­tion. The whole process can be divid­ed into three stages, fuel dry­ing, oxi­da­tion and pro­duc­tion of a com­bustible gaseous sub­stance, which already per­forms the main heat­ing func­tion in the com­bus­tion process.

In the com­bus­tion cham­ber, the loaded fuel is even­ly dis­trib­uted on the grate, which is spe­cial­ly installed at an angle.

The fuel locat­ed on the grate is dried by hot gas­es, after which the process of fuel com­bus­tion with forced air sup­ply already begins. At the end, the gaseous com­bustible mix­ture obtained at the ini­tial stage of com­bus­tion is after­burned in the fur­nace at a tem­per­a­ture of 950‑10000 C. An unin­ter­rupt­ed air sup­ply must be ensured at each stage.
Sol­id fuel residues, ash and soot accu­mu­late in the ash cham­ber, from where it is removed man­u­al­ly.

For ref­er­ence: it should be not­ed that the effi­cien­cy of the boil­er depends on how dense­ly the com­bus­tion cham­ber is loaded with fuel and how the hood works. When the com­bus­tion cham­ber is ful­ly loaded and the air sup­ply is nor­mal, the fuel should burn com­plete­ly, releas­ing the max­i­mum num­ber of kilo­calo­ries dur­ing the com­bus­tion process. The ratio of use­ful sup­ply to boil­er pow­er is a key point dur­ing the oper­a­tion of a sol­id fuel boil­er.

The process­es occur­ring in the com­bus­tion cham­ber also deter­mine the type of boil­er equip­ment. Com­bus­tion can be car­ried out in the usu­al way, thanks to pyrol­y­sis, or for a long time, from top to bot­tom. In each case, a cer­tain ther­mal effect is achieved, which deter­mines the scope of the sol­id fuel boil­er, how the heat­ing of the house is orga­nized.

Heat exchanger — its function

The next most impor­tant struc­tur­al ele­ment of a sol­id fuel boil­er is a heat exchang­er. The device is a cast-iron or steel struc­ture in which ther­mal ener­gy is trans­ferred from com­bus­tion prod­ucts to the coolant. In the tra­di­tion­al ver­sion, the heat exchang­er is made in the form of a bar­rel, through which seam­less boil­er pipes pass. The heat­ed gas­es, pass­ing through the pipes, heat the boil­er water cir­cu­lat­ing inside the heat exchang­er cir­cuit.

Impor­tant! The inten­si­ty of the pas­sage of gas­es through the smoke pipes is reg­u­lat­ed by the posi­tion of the smoke exhauster. The inten­si­ty of water cir­cu­la­tion in the heat exchang­er depends on the oper­a­tion of the pump­ing sta­tion. Heat exchang­ers nec­es­sar­i­ly have a thick lay­er of ther­mal insu­la­tion that pro­tects the main body of the boil­er from over­heat­ing.


The flow of water into the heat exchang­er occurs through the intake man­i­fold, while the exit of the heat­ed coolant, on the con­trary, is car­ried out through the exhaust man­i­fold. On each of the col­lec­tors there are coolant tem­per­a­ture sen­sors. Home heat­ing in a house with a sol­id fuel boil­er, the con­nec­tion dia­gram of which is not much dif­fer­ent from the tra­di­tion­al and gen­er­al­ly accept­ed pro­ce­dure, may have some design dif­fer­ences in each sit­u­a­tion.

Steel heat exchang­ers, unlike cast iron prod­ucts, are more sus­cep­ti­ble to cor­ro­sion, at the same time they suc­cess­ful­ly cope with tem­per­a­ture extremes. The cost of such devices is much less in com­par­i­son with cast iron heat exchang­ers. The lat­ter have a high heat capac­i­ty and are less sus­cep­ti­ble to cor­ro­sion.

Design varieties of systems

If we do not con­sid­er the tra­di­tion­al­ly used stove heat­ing, there are not so many types of sol­id fuel boil­ers that exist today. The main dif­fer­ence between the exist­ing mod­els of boil­ers is the way the fuel is sup­plied. Cheap units are designed for man­u­al fuel sup­ply. In expen­sive mod­els, for the oper­a­tion of a sol­id fuel boil­er, auto­mat­ic fuel sup­ply to the com­bus­tion cham­ber is used.

The method of fuel sup­ply main­ly deter­mines the prin­ci­ple of oper­a­tion of the boil­er. Coal, bri­quettes or fire­wood are loaded into the fire­box and set on fire. The water heat­ed to the required tem­per­a­ture in the coolant diverges through the pipes, heat­ing the liv­ing quar­ters.

On a note: how­ev­er, there is one but! The fuel burns out quick­ly and it is nec­es­sary to load the boil­er with fuel raw mate­ri­als again. The time required for com­plete com­bus­tion of the fuel is lim­it­ed to 2–8 hours, depend­ing on the mod­el of the boil­er and its pow­er. In addi­tion, it is nec­es­sary to simul­ta­ne­ous­ly remove ash from the com­bus­tion cham­ber, the rem­nants of unburned fuel. For the nor­mal oper­a­tion of the boil­er, it is con­stant­ly required to throw more and more por­tions of fuel into the fur­nace.

Auto­mat­ic fuel sup­ply solved the prob­lem with the oper­a­tion of sol­id fuel boil­ers by half. A fun­da­men­tal tech­ni­cal solu­tion was required. For heat­ing with a sol­id fuel boil­er, the best way out of this sit­u­a­tion was the pos­si­bil­i­ty of using heat gen­er­a­tors, which are also called long-burn­ing sol­id fuel boil­ers.

In prac­tice, this type of heat­ing equip­ment is usu­al­ly divid­ed into two types:

The method of load­ing in the equip­ment of these types remained fun­da­men­tal­ly the same, only it became longer in time and more labo­ri­ous. As com­pen­sa­tion for the efforts spent, dur­ing oper­a­tion, the boil­er cre­ates the max­i­mum pos­si­ble ther­mal effect. Despite the dif­fi­cul­ty and com­plex­i­ty of load­ing, in these mod­els there is an almost com­plete com­bus­tion of fuel, which sig­nif­i­cant­ly reduces the num­ber of loads and fuel con­sump­tion.

For pyrol­y­sis boil­ers, the work process is as fol­lows. In the absence of oxy­gen, the com­bus­tion process in the cham­ber slows down. The fuel burns out com­plete­ly, and the coke oven gas obtained as a result of smol­der­ing is a sec­ondary fuel. The oxy­gen-enriched gaseous sub­stance in the com­bus­tion process releas­es addi­tion­al calo­ries of ther­mal ener­gy. There is a high effi­cien­cy, prof­itabil­i­ty and effi­cien­cy of the equip­ment dur­ing oper­a­tion.

Recent­ly, heat­ing of res­i­den­tial build­ings with sol­id fuel boil­ers of upper com­bus­tion has become wide­spread. Fun­da­men­tal­ly, the scheme of work looks a lit­tle dif­fer­ent in com­par­i­son with tra­di­tion­al mod­els. Here, the flame spreads from above, and not from below, as we are usu­al­ly used to see­ing. The com­bus­tion of fuel occurs grad­u­al­ly, from top to bot­tom. At a time when the top lay­er of fuel is sub­ject to intense com­bus­tion, the low­er lay­ers remain untouched. As each lay­er of fuel burns, air, along with com­bustible gas­es, descends. This process can take a very long time, in some mod­els the burn­ing time of one book­mark can be 8–12 hours.

On a note: some mod­els of sol­id fuel boil­ers of upper com­bus­tion in the sup­port­ing mode of oper­a­tion can pro­vide heat from one load for a day or more.

Other important structural elements — their role in the operation of the entire heating system


The scheme of any sol­id fuel boil­er is incon­ceiv­able with­out a draft reg­u­la­tor. This device pro­vides a mechan­i­cal effect on the damper in the chim­ney in the process of turn­ing on or off the unit. You can show the oper­a­tion of the draft reg­u­la­tor using a sim­ple draw­ing.

Thanks to the oper­a­tion of this device, the air sup­ply to the com­bus­tion cham­ber and the heat­ing tem­per­a­ture of the coolant are auto­mat­i­cal­ly adjust­ed.


For ref­er­ence: The reg­u­la­tor is set at the first start-up of the boil­er, set­ting the posi­tion in accor­dance with the set para­me­ters. In a semi-closed posi­tion at a tem­per­a­ture of 650C, in the open posi­tion of the damper, the reg­u­la­tor cor­re­sponds to a max­i­mum tem­per­a­ture val­ue of 900 FROM.

Many units, espe­cial­ly large ones, are installed togeth­er with a buffer tank, which is manda­to­ry when tying sol­id fuel equip­ment with gas boil­ers into a sin­gle sys­tem. Such a device is an expan­sion tank, where the coolant enters. The buffer tank in this case per­forms two func­tions, a hydraulic sep­a­ra­tor and a heat accu­mu­la­tor. As a result of the boil­er cool­ing after shut­down, water from the heat accu­mu­la­tor diverges through the heat­ing radi­a­tors, main­tain­ing the required tem­per­a­ture. Rapid cool­ing of a sol­id fuel boil­er is almost impos­si­ble, due to the fact that the buffer capac­i­ty plays the role of a heat accu­mu­la­tor.

Togeth­er with the buffer tank, the boil­ers are equipped with a ther­mo­sta­t­ic valve. The device is used to pro­tect the sys­tem from over­heat­ing. The cool­ing cir­cuit, equipped with a ther­mo­sta­t­ic valve, will ensure the sup­ply of cold water inside at the first sig­nals of over­heat­ing of the coolant.

For igni­tion in sol­id fuel boil­ers of mod­ern mod­els, var­i­ous gas burn­ers are used. Such devices usu­al­ly run on liq­ue­fied gas, which is stored in a spe­cial tank. Igni­tion of fuel in the com­bus­tion cham­ber due to the use of a gas burn­er occurs in a mat­ter of sec­onds. In oper­a­tion and main­te­nance, such burn­ers are sim­ple and reli­able.


Hav­ing famil­iar­ized your­self with the device and scheme of a sol­id fuel boil­er, hav­ing learned the prin­ci­ple of oper­a­tion of some types of sol­id fuel boil­er equip­ment, you can safe­ly pro­ceed to cre­ate your own autonomous heat­ing sys­tem in your own house. Choos­ing a boil­er is not par­tic­u­lar­ly dif­fi­cult. The main bur­den and dif­fi­cul­ties that will have to be faced in the future are the instal­la­tion of equip­ment, con­nec­tion and prepa­ra­tion for launch.

A com­pe­tent and qual­i­fied approach at each stage will allow you to achieve the desired result.


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