Solid fuel boiler with buffer tank: what is its use?


Installing a sol­id fuel boil­er in a res­i­den­tial build­ing is both a sim­ple and under­stand­able task, but upon clos­er exam­i­na­tion, it is asso­ci­at­ed with numer­ous tech­ni­cal and tech­no­log­i­cal dif­fi­cul­ties. Today, many cit­i­zens seek to equip their home with a sol­id fuel heat­ing device. This is due to the good per­for­mance char­ac­ter­is­tics of this type of heat­ing equip­ment, the absence of the need to obtain per­mis­sion to install a sol­id fuel heater. Not the last role in terms of choos­ing heat­ing equip­ment is played by the cost of the fuel resource and its rel­a­tive avail­abil­i­ty.

How­ev­er, choos­ing a boil­er and installing it in the house is not enough. For the nor­mal oper­a­tion of the autonomous heat­ing sys­tem, addi­tion­al instal­la­tion of var­i­ous devices, devices and mech­a­nisms will be required. Most of these devices ensure the nor­mal func­tion­ing of the entire heat­ing com­plex and its safe­ty. A buffer tank or a heat accu­mu­la­tor for a sol­id fuel boil­er just belongs to the cat­e­go­ry of such devices, with­out which not a sin­gle heat­ing unit can ful­ly work. What is a buffer capac­i­ty, let’s look at it in detail?

The place of the buffer tank in the autonomous heating system

Not each of us is able to com­pre­hend and imag­ine how home heat­ing should look like in the opti­mal ver­sion and how this or that mech­a­nism should work. Heat­ing devices are only a source of ther­mal ener­gy, with the help of which the heat car­ri­er is heat­ed, which already diverges along the heat­ing cir­cuit. In order for the whole process to pro­ceed as effi­cient­ly as pos­si­ble and at the same time, the safe­ty of the oper­a­tion of the heat­ing unit was ensured, a buffer tank is nec­es­sar­i­ly includ­ed in the pip­ing.

With­out this device, your sol­id fuel boil­er (any heat­ing device) will be a time bomb, which, at the slight­est fail­ure in the sys­tem, can cause a lot of trou­ble and trou­ble.

To answer the ques­tion why you need to install such a large unit at home, an analy­sis of the prin­ci­ple of oper­a­tion of a sol­id fuel boil­er will help.

On a note: instal­la­tion of sol­id fuel units, oper­a­tion of boil­ers with­out a buffer tank in the USA, in many Euro­pean coun­tries is pro­hib­it­ed.

In fact, the name of the device explains its pur­pose. Its main task is to play the role of a buffer between a work­ing boil­er and a heat­ing sys­tem. The task of the buffer is to reduce or increase the heat capac­i­ty of the coolant cir­cu­lat­ing in the heat­ing cir­cuit. Due to its vol­ume, the con­tain­er is able to influ­ence the tem­per­a­ture regime of the degree of heat­ing of boil­er water.

From the point of view of mechan­ics, the con­tain­er is an ordi­nary ther­mos, i.e. met­al inte­gral ves­sel, insu­lat­ed on the out­side with insu­lat­ing mate­r­i­al. By loca­tion, this device is inex­tri­ca­bly linked with the heat­ing device. The stor­age tank is installed in the imme­di­ate vicin­i­ty of the boil­er. What is this bulky unit in the heat­ing sys­tem for? Every­thing explains the mode of oper­a­tion of heat­ing devices and the fea­tures of their design.

The principle of operation of the device


Each heater has its own, spe­cial prin­ci­ple of oper­a­tion. Some boil­ers are char­ac­ter­ized by a uni­form mode of oper­a­tion (gas and elec­tric heat­ing equip­ment), while oth­ers, on the con­trary, are char­ac­ter­ized by an unsta­ble process. The inten­si­ty of heat­ing depends on the method of fuel sup­ply and the pres­ence of devices that con­trol the com­bus­tion process. With appli­ances run­ning on nat­ur­al gas or elec­tric­i­ty, every­thing is sim­ple and clear. To reg­u­late the heat­ing tem­per­a­ture of the coolant, it is enough to reduce or even stop the gas sup­ply, turn off the pow­er sup­ply. Con­stant pow­er sup­ply ensures unin­ter­rupt­ed oper­a­tion of boil­er equip­ment. Both day and night, the boil­er oper­ates in auto­mat­ic mode, inde­pen­dent­ly adjust­ing the heat­ing tem­per­a­ture of the coolant.

Sol­id fuel boil­ers are units with high iner­tia. The fuel put into the fur­nace burns con­stant­ly, and it is phys­i­cal­ly impos­si­ble to stop this process quick­ly. The ther­mal ener­gy obtained in the com­bus­tion process should not be wast­ed. Excess heat is accu­mu­lat­ed togeth­er with the coolant in a spe­cial con­tain­er, which acts as a ther­mal ener­gy accu­mu­la­tor.

The sit­u­a­tion is sim­i­lar with a decrease in the inten­si­ty of the boil­er. When the fuel mass is burned, the boil­er abrupt­ly los­es its per­for­mance, the boil­er water in the heat­ing cir­cuit begins to cool rapid­ly. With­out anoth­er por­tion of fuel, there is a threat of a decrease in tem­per­a­ture in heat­ed rooms. Of course there is a way out. A new book­mark of fire­wood or coal will solve the prob­lem. Anoth­er ques­tion is how often you can do this pro­ce­dure, espe­cial­ly if the fire­box turned out to be emp­ty at night.

A sol­id fuel boil­er con­nect­ed to a buffer tank is a com­plex that can solve the prob­lem of heat­ing res­i­den­tial premis­es for you. Installing a buffer tank frees you from the fre­quent and hard work of load­ing the com­bus­tion cham­ber of the heater with the next amount of fire­wood.

On a note: It has been cal­cu­lat­ed that a cor­rect­ly cal­cu­lat­ed heat accu­mu­la­tor (buffer tank) sig­nif­i­cant­ly reduces the num­ber of fur­nace loads with fuel mate­r­i­al. On aver­age, the num­ber of loads decreas­es, depend­ing on the mod­el and type of boil­er, by 2 times. There is a real sav­ing of your per­son­al time and fuel resource (by 30–50%).

You can under­stand the prin­ci­ple of oper­a­tion of the buffer capac­i­ty using the exam­ple of a car bat­tery. While the engine is run­ning in the car, the elec­tric cur­rent gen­er­a­tor is run­ning in par­al­lel. The elec­tric­i­ty gen­er­at­ed by the gen­er­a­tor is stored in the bat­tery. When the main engines stop, the bat­tery gives back the nec­es­sary ener­gy to the auto­mo­tive sys­tems.

The buffer tank works the same way. There is heat, the heat accu­mu­la­tor accu­mu­lates it, as soon as the heat­ing instal­la­tion stops pro­duc­ing heat, hot water from the stor­age tank is used to heat all heat­ing sys­tems.

What else is the use of buffer capacity. Main advantages


In addi­tion to its direct pur­pose, the hot water stor­age device per­forms a num­ber of oth­er equal­ly use­ful func­tions. Heat­ing units oper­at­ing on sol­id fuels, as a rule, have dif­fer­ent stages of com­bus­tion. This is the moment of igni­tion, intense com­bus­tion and, accord­ing­ly, the process of atten­u­a­tion. At the sec­ond stage, dur­ing inten­sive com­bus­tion, the boil­er pro­duces the max­i­mum amount of ther­mal ener­gy, more than is nec­es­sary for heat­ing. In the ini­tial and final stages, when the fuel is just start­ing to burn or run­ning out, the heaters are far from their rat­ed pow­er.

A sim­i­lar mode of oper­a­tion of sol­id fuel appa­ra­tus­es with­out addi­tion­al equip­ment usu­al­ly caus­es a num­ber of domes­tic incon­ve­niences. The fact that dif­fer­ences with the tem­per­a­ture of the coolant in the heat­ing cir­cuit are pos­si­ble has already been said.

Impor­tant! The hot water stor­age tank will not allow, in the event of a long absence of fuel in the fur­nace, to defrost either the boil­er itself or the entire heat­ing sys­tem. Some mod­els of buffer tanks are capa­ble of sup­ply­ing warm water to the boil­er and to the heat­ing cir­cuit for 12–24 hours. What is impor­tant for res­i­dents of remote areas.

In the absence of a heat accu­mu­la­tor, when domes­tic hot water is inten­sive­ly used in the house, prob­lems can­not be avoid­ed. The buffer tank is just designed to elim­i­nate the result­ing drops in the heat­ing of res­i­den­tial premis­es and ensure the nor­mal oper­a­tion of the DHW sys­tem.

The advan­tages of using a stor­age tank are obvi­ous, and know­ing about them, you will no longer look skep­ti­cal­ly at a bulky tank in your boil­er room. Installing a buffer tank in a domes­tic heat­ing sys­tem pro­vides the fol­low­ing ben­e­fits:

  • oper­a­tion of sol­id fuel heat­ing units in eco­nom­i­cal mode;
  • increase in time inter­vals between load­ing fuel into the boil­er;
  • the abil­i­ty to use heaters in the sum­mer for the oper­a­tion of the hot water sys­tem;
  • tech­ni­cal abil­i­ty to use high-pow­er heat­ing units in rooms with low heat loss;
  • sim­ple and clear design of the device does not require spe­cial main­te­nance and has a long ser­vice life;
  • sta­t­ic state of the device that does not cre­ate domes­tic incon­ve­nience;

Instal­la­tion of a con­tain­er of suf­fi­cient vol­ume allows the instal­la­tion of oth­er heat­ing devices in res­i­den­tial premis­es.

For exam­ple: when sev­er­al heat­ing units of dif­fer­ent types are includ­ed in the autonomous heat­ing sys­tem at once. Often in pri­vate house­holds, sol­id fuel boil­ers are installed paired with elec­tri­cal appli­ances. Both units can be freely con­nect­ed to one heat stor­age device, and for this pur­pose it is not nec­es­sary to install addi­tion­al parts in the sys­tem. Thanks to the buffer capac­i­ty, both units can be con­fig­ured to work in terms of pri­or­i­ty, bal­ance their work as need­ed.

Assess­ing the ben­e­fits that the instal­la­tion of a buffer tank gives to the heat­ing sys­tem, one should not for­get about safe­ty.

For any heat­ing devices, the main dan­ger is over­heat­ing. A work­ing sol­id fuel boil­er con­stant­ly needs to be mon­i­tored. The large iner­tia of this type of equip­ment often caus­es over­heat­ing, as a result of which the unit can fail, and in the worst case, lead to extreme­ly unpleas­ant con­se­quences. The hot water stor­age tank eas­i­ly elim­i­nates this prob­lem by remov­ing excess load on the heater.

How to choose the right heat accumulator for your heating system

Before installing the heat­ing sys­tem, they are deter­mined with the type of main heat source. The vol­ume of the heat accu­mu­la­tor also depends on the pow­er of the sol­id fuel boil­er and the vol­ume of tasks that the device will solve dur­ing oper­a­tion. The size and vol­ume of the dri­ve is also deter­mined by your house­hold needs. When choos­ing a buffer tank, the mod­el of the heat­ing unit, which has a pow­er lim­it and a lim­it­ed time resource, becomes a pri­or­i­ty.

In oth­er words:

  • when work­ing in tan­dem with a sol­id fuel boil­er, the buffer tank must ensure the accu­mu­la­tion of ther­mal ener­gy dur­ing a one-time fuel load, which is enough to dis­trib­ute the hot coolant through the sys­tem until the sub­se­quent load­ing of the com­bus­tion cham­ber.

Here it is appro­pri­ate to say a few words about the cal­cu­lat­ed data that affect the choice of the opti­mal vol­ume of buffer capac­i­ty. With the help of cal­cu­la­tions, it is pos­si­ble to deter­mine the actu­al stor­age capac­i­ty of a par­tic­u­lar vol­ume of coolant, which has an impact on the heat capac­i­ty.

It is con­sid­ered to be: the heat capac­i­ty of boil­er water is 4.187 kJ kg/ 0C, which in turn means. For heat­ing 1 kg. water for just 10C, an amount of ther­mal ener­gy in the equiv­a­lent of 4.187 kJ will be required. For heaters, this val­ue is 1 kcal = 1.163 W / h.


For the sake of com­plete­ness, we con­sid­er When installing a heat accu­mu­la­tor with a vol­ume of 1000 liters. (1000 kg.), for heat­ing water up to a tem­per­a­ture of 500C, the amount of ther­mal ener­gy stored in the tank will be 1000 x 50 = 50000 kcal or 580$ kWh.

When hot water is con­sumed from the buffer tank and the water tem­per­a­ture drops by 50 degrees, the amount of heat will cor­re­spond­ing­ly decrease by the same val­ue. Each con­nec­tion scheme has its own method for cal­cu­lat­ing the capac­i­ty of a heat stor­age device, how­ev­er, there are the fol­low­ing gen­er­al require­ments that must be tak­en into account:

  • the stor­age tank must be capa­ble of accu­mu­lat­ing the max­i­mum amount of excess ther­mal ener­gy dur­ing the com­bus­tion of fuel at a sin­gle load;
  • the high­er the peak heat con­sump­tion in the heat­ing cir­cuit and the longer the max­i­mum heat con­sump­tion, the more vol­ume is required for the buffer tank;
  • in case of high com­bus­tion inten­si­ty of the boil­er in short peri­ods of time, it will be nec­es­sary to install an addi­tion­al heat exchang­er, either sep­a­rate­ly or inte­grat­ed into the buffer tank;
  • the accu­mu­la­tor must have a nom­i­nal pres­sure inside greater than at the point of con­nec­tion of the device to the sys­tem;
  • in hot water tanks with two or more built-in heat exchang­ers, a sys­tem with a low­er work­ing pres­sure is con­nect­ed to the low­er heat exchang­ers, and with a strong work­ing pres­sure, on the con­trary, to the heat exchang­ers locat­ed at the top;
  • the instal­la­tion of a heat accu­mu­la­tor oblig­es the instal­la­tion of an expan­sion tank and a safe­ty, ther­momix­ing valve in the sys­tem.


The cor­rect cal­cu­la­tion of the ther­mal capac­i­ty of the coolant accu­mu­lat­ed in the accu­mu­la­tors will allow the sol­id fuel boil­er to oper­ate in nor­mal mode. The buffer tank, com­plete with oth­er safe­ty ele­ments, not only ensures the unin­ter­rupt­ed oper­a­tion of the heat­ing sys­tem, but also nor­mal hot water sup­ply. The buffer tank, which is also a heat accu­mu­la­tor, guar­an­tees not only the safe oper­a­tion of heat­ing devices, but is also eco­nom­i­cal­ly fea­si­ble.

The only nuance that you will have to pay atten­tion to when equip­ping a home heat­ing sys­tem is the choice of a place for a boil­er room. Mount­ing a large vol­ume tank will require a tech­no­log­i­cal solu­tion from you. In some cas­es, heat accu­mu­la­tors are assem­bled on site.


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