The principle of operation and features of the operation of solid fuel air heating boilers


Of all the meth­ods of heat­ing that exist today, air heat­ing is con­sid­ered the rarest. Despite the fact that even 50–70 years ago these heat­ing sys­tems were pop­u­lar and were installed in large quan­ti­ties, today it is rather dif­fi­cult to find such objects. The excep­tions are fire­places and tra­di­tion­al Euro­pean stoves, which are not full-fledged air heat­ing sys­tems.

Of all the equip­ment and devices that work on the same prin­ci­ple, we are most famil­iar with heat guns, fan heaters and con­vec­tors. Heat­ing, where the main focus is on sol­id fuel boil­ers that pro­vide air heat­ing, is used today in rare cas­es. Con­sid­er the rea­sons why air heat­ing is not as pop­u­lar today as oth­er types of heat­ing. Let’s deal with the prin­ci­ple of oper­a­tion of an air heat­ing device that runs on sol­id fuel.

The essence of air heating. Main advantages

An air heat­ing sys­tem is a com­plex of devices and devices that close­ly inter­act with each oth­er. As in oth­er heat­ing meth­ods, here the ther­mal ener­gy obtained as a result of com­bus­tion is trans­ferred to the sur­round­ing space, objects. The essen­tial dif­fer­ence of this method lies in the absence of a coolant, which plays the role of an inter­me­di­ary in most heat­ing sys­tems. Heat­ing of premis­es is car­ried out due to the cir­cu­la­tion of air heat­ed to a cer­tain tem­per­a­ture.

There are two types of air exchange: nat­ur­al air cir­cu­la­tion and forced.


Look­ing at a burn­ing fire­place, you can rough­ly imag­ine how air heat­ing works. How­ev­er, here the heat as a result of burn­ing fire­wood is not spent ratio­nal­ly, most of it is wast­ed. It is fun­da­men­tal­ly impor­tant to force the heat­ed air to move through the duct and give off heat to the heat­ed rooms. This is what a sol­id fuel boil­er does in the air heat­ing sys­tem.

The main advan­tages that air heat­ing and a heat­ing device of this type have are as fol­lows:

  • lack of great iner­tia. In com­par­i­son with water boil­ers, the air heat­ing unit warms up quick­ly enough and in the same way cools down faster;
  • sim­ple and unpre­ten­tious in work design of heat­ing devices. Low cost of boil­er equip­ment oper­at­ing on the prin­ci­ple of air heat­ing;
  • good resis­tance of the entire sys­tem and the heat­ing boil­er in par­tic­u­lar to low tem­per­a­tures. The absence of a liq­uid coolant allows you to safe­ly leave the heat­ing equip­ment turned off for a long time;
  • fast and con­cealed instal­la­tion. No need to lay a pip­ing sys­tem and install heat­ing radi­a­tors.

In each case, there is some­thing to think about. The low iner­tia of air heat­ing units is one of the sig­nif­i­cant advan­tages. When installing such equip­ment, you do not have to install either a buffer tank or heat accu­mu­la­tors. The boil­er is brought to the opti­mal oper­at­ing mode in a mat­ter of min­utes. The same fac­tor plays an impor­tant role in terms of equip­ment resis­tance to low tem­per­a­tures. In the absence of a liq­uid heat car­ri­er, you should not be afraid of defrost­ing the sys­tem dur­ing the cold peri­od.

If we talk about the cost of equip­ment, then sol­id fuel air boil­ers are sig­nif­i­cant­ly infe­ri­or in price to their coun­ter­parts work­ing with water heat­ing sys­tems. Alu­minum pipes for air ducts are an order of mag­ni­tude cheap­er than the mate­ri­als and com­po­nents required for pip­ing equip­ment in a house.

For ref­er­ence: Heat­ing of res­i­den­tial premis­es in this way was first used in ancient Rome. In the hous­es of noble nobles, in pub­lic places, air stoves were used, which had to be heat­ed with fire­wood.

The cir­cu­la­tion of the heat­ed air mass was car­ried out in a nat­ur­al way, due to the action of the laws of physics. When air is heat­ed, it expands, con­vec­tion process­es occur, lead­ing to the appear­ance of nat­ur­al draft. Hot air spreads, and a new por­tion of fresh, cool air takes its place. Even in antiq­ui­ty, the great impor­tance of ven­ti­la­tion was dis­cov­ered to achieve greater effi­cien­cy of heat­ing mea­sures. The inten­si­ty of com­bus­tion and the move­ment of heat­ed air mass­es direct­ly depend on the pos­si­bil­i­ty of inflow and out­flow. The greater the thrust, the high­er the inten­si­ty of com­bus­tion and, accord­ing­ly, the heat­ing of the air. The thrust decreas­es, the inten­si­ty of all the process slows down.


Today, instead of prim­i­tive air ovens, sol­id fuel heat­ing devices have come. Air sol­id fuel units are able to more effi­cient­ly and effi­cient­ly heat the air mass for space heat­ing. Mod­ern mod­els are char­ac­ter­ized by high effi­cien­cy, eco­nom­i­cal and easy to use. The air heat­ing sys­tem is con­sid­ered unde­served­ly for­got­ten.

An important technical aspect

The main rea­son for this atti­tude to air heat­ing was the tech­no­log­i­cal require­ments asso­ci­at­ed with the orga­ni­za­tion of the heat­ing process. There is one tech­ni­cal nuance of air heat­ing, which over time has grown into a clear dis­ad­van­tage.

For exam­ple:

Your heat­ing boil­er is locat­ed in the boil­er room and in order for warm air to get into oth­er rooms, it is nec­es­sary to have a devel­oped air duct sys­tem. There is not always a phys­i­cal and con­struc­tive pos­si­bil­i­ty to lay air duct chan­nels that are suf­fi­cient­ly large in cross sec­tion in a lim­it­ed space.

The prin­ci­ple of oper­a­tion of air heat­ing is not com­pli­cat­ed. The main process pro­ceeds in a sim­ple and uncom­pli­cat­ed way. With the ven­ti­la­tion sys­tem of a sol­id fuel air boil­er, the issue can still be solved some­how by plac­ing the main com­mu­ni­ca­tions under the ceil­ing. The flow of hot air is pro­vid­ed by the low­er loca­tion of the air duct. Due to the tem­per­a­ture dif­fer­ence between warm and cold air, con­vec­tion occurs, and air mass­es are replaced. In oth­er words, with the exist­ing draft in the room, the desired effect can be achieved. Whether you like con­stant drafts at home or not, it’s up to you.

Anoth­er, no less impor­tant detail that fol­lows from the phys­i­cal prop­er­ties of air exchange, which should be paid atten­tion to, is the low­er loca­tion of the air ducts. Usu­al­ly, for these pur­pos­es, air ducts are laid under­ground, between the lags, or the air duct is equipped direct­ly in the wall pan­els. When re-equip­ping the premis­es or replac­ing com­mu­ni­ca­tion lines, it is nec­es­sary to take into account the pres­ence of air chan­nels in the struc­tur­al ele­ments of the build­ing. This is the main design flaw that marks the air heat­ing sys­tem.

Impor­tant! The low­er loca­tion of the duct allows the use of nat­ur­al cir­cu­la­tion. With the option with the top arrange­ment of air chan­nels, it will be nec­es­sary to install a blow­er for forced cir­cu­la­tion and increase the speed of the air flow.

Solid fuel boiler — the main source of heat. Principle of operation


How do we imag­ine a sol­id fuel boil­er due to which the home heat­ing sys­tem func­tions? This is a pyrol­y­sis-type heat­ing device famil­iar to many of us. Due to the com­bus­tion, first of fuel, and then of com­bustible wood gas, there is an intense release of heat from the inter­ac­tion, with which the heat exchang­er is heat­ed. More pre­cise­ly, an air exchang­er. Heat­ed to a cer­tain tem­per­a­ture in the pipes of the heat exchang­er, the air cir­cu­lates through the duct sys­tem, heat­ing the inte­ri­or.

Such a heat­ing device can be installed almost any­where in a res­i­den­tial build­ing or oth­er premis­es.

On a note: Today, mod­els of sol­id fuel air heat­ing units are pro­duced, the design and appear­ance of which allows them to suc­cess­ful­ly fit into the inte­ri­or of res­i­den­tial premis­es.

If the own­er of the house wish­es, the air can be dis­trib­uted through the duct nat­u­ral­ly or under the action of blow­ers, which sig­nif­i­cant­ly increas­es the speed and den­si­ty of the air flow. The boil­er has, as a rule, a spa­cious com­bus­tion cham­ber where the fuel burns. The fur­nace has a spe­cial hatch through which fire­wood is loaded. At the bot­tom of the com­bus­tion cham­ber there is a grate on which the fuel is placed and the com­bus­tion itself is car­ried out direct­ly. As in oth­er sol­id fuel units, a pod­zol­nik is locat­ed in the low­er part of the struc­ture — a box for col­lect­ing ash and large remains of unburned wood.

Air boiler device

If pref­er­ence is giv­en to the pyrol­y­sis method of fuel com­bus­tion, then a boil­er equipped with two com­bus­tion cham­bers is required. In one com­part­ment, as a result of the smol­der­ing of the fuel mass, an inten­sive release of wood gas is car­ried out. In the sec­ond fur­nace, volatile com­bustible com­pounds, react­ing with oxy­gen, ignite, releas­ing a huge amount of ther­mal ener­gy. This method is fuel effi­cient. In the process of burn­ing fire­wood, there are prac­ti­cal­ly no large resid­ual frag­ments left. The air heat­ing sys­tem with a pyrol­y­sis-type sol­id fuel boil­er is dis­tin­guished not only by fast and high-qual­i­ty heat­ing of rooms, but also by high per­for­mance.


Heat­ed air accu­mu­lates in the space between the body of the heat­ing unit and the fire­box (com­bus­tion cham­ber). This is the heat exchang­er in this case.

Due to the influx of air, the walls of the com­bus­tion cham­ber are con­stant­ly washed by new air flows. Both pri­ma­ry and sec­ondary air are used for heat­ing. Thanks to pyrol­y­sis in the boil­er, pri­ma­ry and sec­ondary air do the main work. Pri­ma­ry air mass­es are the main source of heat. Air enter­ing from out­side, i.e. pre­heat­ed to reduce heat loss, and only then enters the fur­nace. Sec­ondary air is a gas-air mix­ture con­sist­ing of air and hot com­bus­tion prod­ucts.

On a note: sol­id fuel in most cas­es burns down by 90%. The remain­ing 10% are pre­sent­ed in the form of the small­est par­ti­cles that make up the smoke. The main advan­tage of sec­ondary air is that it already has a high tem­per­a­ture. Addi­tion­al heat­ing is not required to reach the required tem­per­a­ture. Due to such air exchange, a high heat capac­i­ty of the oper­at­ing unit is achieved, and the effi­cien­cy of heat­ing equip­ment increas­es.

The selec­tion of sec­ondary air mass­es is car­ried out from the upper­most part of the duct. The inten­si­ty of the intake is reg­u­lat­ed by the posi­tion of the damper. The inten­si­ty of com­bus­tion on this equip­ment deter­mines the amount of air sup­plied to the com­bus­tion cham­ber. More air, more intense com­bus­tion. Air sup­ply in sim­ple mod­els is car­ried out in man­u­al mode, due to the nat­ur­al flow of air. In expen­sive mod­els, a fan is used for this pur­pose, which turns on and off auto­mat­i­cal­ly. Such fans are called blow­ers. In order to achieve the max­i­mum pos­si­ble effect of the boil­er oper­a­tion, a smoke exhauster is installed on the chim­ney, the task of which is to improve the removal of resid­ual com­bus­tion prod­ucts from the com­bus­tion cham­ber.

To date, sol­id fuel air units of var­i­ous degrees of equip­ment are on sale. Most mod­els include:

  • igni­tion;
  • com­bus­tion process con­trol sys­tem (tem­per­a­ture sen­sors, dampers, blow­ers);
  • mech­a­nisms and devices that sup­ply fuel.

Due to the inter­ac­tion of all sys­tems, the boil­er allows you to con­trol the heat­ing tem­per­a­ture in the premis­es.

Features of the air heating system


The air heat­ing sys­tem has its own tech­ni­cal fea­tures and nuances that must be tak­en into account dur­ing instal­la­tion. Approx­i­mate­ly the fol­low­ing val­ues ​​​​are tak­en for cal­cu­la­tions:

  • the aver­age air con­sump­tion for an autonomous heat­ing sys­tem is 1000–4000 m3/hour;
  • the pres­sure in the sys­tem should be 150 Pa;
  • hot air boil­er pow­er (depend­ing on mod­el and type);
  • the amount of heat loss in res­i­den­tial premis­es.

Cal­cu­la­tions are car­ried out in order to achieve the max­i­mum pos­si­ble effect from a work­ing heat­ing sys­tem. Lack of accu­rate cal­cu­la­tions can lead to the fol­low­ing neg­a­tive con­se­quences:

  • heater over­heat­ing:
  • duct vibra­tion, addi­tion­al tech­ni­cal noise;
  • con­stant drafts inside the build­ing.

The length of the main air duct should not exceed 30 m. Branch­es should not be longer than 15 meters. For the oper­a­tion of a home heat­ing sys­tem, sol­id fuel air boil­ers with a capac­i­ty of 10–50 kW are suf­fi­cient. Large premis­es with exten­sive inte­ri­or space require the instal­la­tion of units of much high­er pow­er (up to 1 MW). Large indus­tri­al build­ings, shop­ping cen­ters and premis­es of social and urban infra­struc­ture, as a rule, are heat­ed by high-capac­i­ty air sol­id fuel devices (up to 5–10 MW).

Impor­tant! When choos­ing a mod­el, rang­ing from the sim­plest (Bulleryan type) to the most com­plex and pow­er­ful pyrol­y­sis-type units, it is nec­es­sary to pro­vide a mech­a­nism for adjust­ing the inten­si­ty of fuel com­bus­tion.

Exist­ing auto­mat­ic damper move­ment sys­tems will allow you to sig­nif­i­cant­ly increase the safe­ty of boil­er equip­ment and reduce the like­li­hood of exces­sive fuel con­sump­tion.


Sol­id fuel boil­ers are again becom­ing of inter­est to a wide range of con­sumers. The main advan­tage that they have, effi­cien­cy and sim­ple oper­a­tion, are the main trump cards of such equip­ment. For pri­vate and coun­try hous­es today it is much eas­i­er to equip an air heat­ing sys­tem. The absence of com­plex addi­tion­al mech­a­nisms and devices, con­ve­nient adjust­ment by process­es, makes such units very con­ve­nient and prac­ti­cal in oper­a­tion.

Air heat­ing units, unlike hot water boil­ers, have an order of mag­ni­tude longer ser­vice life. In terms of secu­ri­ty, this tech­nique seems to be prefer­able.


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