Calculation of underfloor heating: power and energy consumption


The use of under­floor heat­ing as the main or addi­tion­al source of heat­ing for a house or apart­ment is a pop­u­lar “inno­va­tion” that has come to our coun­try rel­a­tive­ly recent­ly. Com­pared to tra­di­tion­al meth­ods, this heat­ing method is more effi­cient and eco­nom­i­cal.

But, in order for such a sys­tem to work “like clock­work”, with max­i­mum heat trans­fer, before instal­la­tion, it is impor­tant to make a com­pe­tent cal­cu­la­tion of the heat of a warm floor, tak­ing into account the pecu­liar­i­ties of its struc­ture and func­tion­ing.

The design of the warm water floor system

Water type floors have a fair­ly sim­ple design. In sim­ple terms, they are con­crete slabs, with a heat­ing ele­ment inside, the func­tion of which is per­formed by pipes filled with hot water. The coolant enters the pipeline from the dis­tri­b­u­tion of the main heat­ing sys­tem and, after pass­ing through the full cycle, returns back. That is, we can con­di­tion­al­ly say that a warm floor is the same heat­ing radi­a­tor, only of a hor­i­zon­tal type, mount­ed on the basis of the room and pro­tect­ed from loads and dam­age dur­ing oper­a­tion with a con­crete screed.

Such a sys­tem con­sists of sev­er­al lay­ers fol­low­ing one after anoth­er.. It:

heated tile

  1. Basepre­vi­ous­ly lev­eled and pre­pared accord­ing­ly.
  2. Water­proof­ing past­ing or coat­ing type. In the first case, its func­tion is per­formed by mate­ri­als based on bitu­men with poly­mer addi­tives, rein­forced with fiber­glass or poly­ester. The sec­ond group is rep­re­sent­ed by mas­tics of bitu­men-rub­ber, bitu­men-poly­mer or cement-poly­mer type.
  3. Ther­mal insu­la­tion lay­er. To cre­ate it, foam or EPS (extrud­ed poly­styrene foam) is used. The thick­ness of this “lay­er” is deter­mined by the cal­cu­la­tion method.
  4. Roll insu­la­tion with a reflec­tive sur­face (shield­ing sub­strate).
  5. Pipesinclud­ed in the under­floor heat­ing sys­tem.
  6. Con­crete screedmade with the addi­tion of a plas­ti­ciz­ing com­pound and addi­tion­al­ly rein­forced with a rein­forced mesh with cells of 100 x 100 mm, from a wire with a cross sec­tion of 3–4 mm.
  7. Fin­ish floor­ing.

How is heat distributed through pipes?

It oper­ates as fol­lows:

  • Through the pres­sure pipe, the coolant (water), heat­ed to the opti­mum tem­per­a­ture, enters the under­floor heat­ing cir­cuit.
  • Hav­ing passed through the pipeline sys­tem, it trans­fers its heat to the screed, heat­ing it to a tem­per­a­ture of approx­i­mate­ly 27–36 C⁰.
  • The cooled water moves to the return line, through which it flows into the boil­er, where it is heat­ed again.

That is, in fact, one of the main ele­ments of the heat­ing struc­ture is ther­mal insu­la­tion.. Accord­ing­ly, when cal­cu­lat­ing a warm water floor, it is nec­es­sary to choose its thick­ness cor­rect­ly.

For “cold bases” locat­ed above an unheat­ed base­ment or soil, it should be at least 50 mm with a heat insu­la­tor den­si­ty of 25 kg / m³.

Data required for the design of under­floor heat­ing devices:

  • Apart­ment plan or hous­es (with all floors).
  • Infor­ma­tion about type and com­po­si­tion of walls, win­dows and doors.
  • Instruc­tions regard­ing tem­per­a­ture regimeplanned indoors.
  • Infor­ma­tion about the place of instal­la­tion of the heat­ing boil­er and its loca­tion rel­a­tive to the floor lev­el.
  • Num­ber of out­lets and ris­ers inside the house.

Based on these indi­ca­tors, the cal­cu­la­tion of heat­ing with warm floors is made. First of all, for this a project plan is being drawn upwhich includes the fol­low­ing infor­ma­tion:

  • Num­ber of heat­ing radi­a­torscon­nect­ed to the sys­tem, their type and loca­tion.
  • Scheme of the future loca­tion of the pipeline with pipe diam­e­ters and lengths of straight sec­tions.
  • Pipe lay­out indi­cat­ing the dis­tances between them and the tem­per­a­ture of the coolant (these two points can be com­bined).
  • Radi­a­tor pow­er datainclud­ed in the sys­tem.
  • Set­ting Infor­ma­tion its auto­mat­ic part.

Power calculation

After draw­ing up a plan and project of the heat­ing sys­tem, the pow­er of the warm floor is cal­cu­lat­ed. This fig­ure will depend on the fol­low­ing fac­tors:

  • Area and type of heat­ed room.
  • Fea­tures of its design and the nature of future oper­a­tion.

Accord­ing to these indi­ca­tors, you need to select heat source pow­er. It is cal­cu­lat­ed using the fol­low­ing for­mu­la:

Mn = 1.2 * Qwhere­in

MP is the ther­mal pow­er;

Q – heat loss dur­ing oper­a­tion;
heating safety
1.2 — safe­ty fac­tor, vary­ing from 1 to 1.2 units.

That is, in order to make a hydraulic cal­cu­la­tion of a warm floor, it is nec­es­sary deter­mine the amount of heat lossaris­ing dur­ing its oper­a­tion. They are equal:

Q = (V * Pt * k) / 860

V — the vol­ume of the room (it is found by mul­ti­ply­ing the area by the height of the ceil­ings);

Pt — the tem­per­a­ture dif­fer­ence between inside and out­side the premis­es (to deter­mine it, +20 C⁰ is tak­en as a basis — the tem­per­a­ture com­fort­able for a per­son in the room and the small­est neg­a­tive val­ue char­ac­ter­is­tic of this cli­mat­ic zone in win­ter, for exam­ple ‑30 C⁰, etc.).

K — coef­fi­cient of heat resis­tance of the house (from 1.5 to 2).

Here it is nec­es­sary to remem­ber that if the amount of heat loss per 1 sq.m of area exceeds 100 W, the room needs addi­tion­al insu­la­tion. This is due to the fact that poor ther­mal insu­la­tion can lead to heat loss­es of up to 80 watts per square meter. m.

For those who find these cal­cu­la­tions too com­pli­cat­ed, a spe­cial pro­gram for cal­cu­lat­ing a warm water floor, which can be found on the Inter­net, can help. Exam­ple: etc.

It is bet­ter to entrust the per­for­mance of basic design cal­cu­la­tions and the selec­tion of mate­r­i­al when lay­ing the floor to qual­i­fied spe­cial­ists in this field. The same applies to the cal­cu­la­tion of the elec­tric floor heat­ing.

heat distribution in the house

In addi­tion to the pow­er of the heat­ing sys­tem and the qual­i­ty of the ther­mal insu­la­tion of the house, the heat in it will depend on oth­er fac­tors.for exam­ple:

  • Thick­ness and type of insu­la­tion gen­der.
  • Vari­eties of floor­ing.
  • Num­ber of win­dows indoors and the method of their glaz­ing.
  • Room loca­tion rel­a­tive to oth­er rooms in the house, etc.

The next step in the design of this heat­ing sys­tem is the cal­cu­la­tion of the pipe pitch for under­floor heat­ing. The uni­for­mi­ty of space heat­ing and the required length of the pipeline depend on this.

Cal­cu­la­tion of the length of the warm floor can be done inde­pen­dent­ly, tak­ing as a basis the data on the required pow­er of the heat­ing sys­tem, com­par­ing the area of ​​u200bu200bthe pipeline with the tem­per­a­ture of the coolant run­ning in the sys­tem, accord­ing to the for­mu­la:

L=S/N*1.1, where:

L — pipe length;

S — the area of ​​the heat­ed room;

N — lay­ing step;

1.1 — pipeline mar­gin of 10% (for bends).

When cal­cu­lat­ing a pipe for a warm floor, in this way, the length of the pipe to the col­lec­tor, includ­ing dis­tri­b­u­tion and return, must also be added to the val­ue obtained.

In addi­tion, the cal­cu­la­tion of the warm floor by area is car­ried out by a graph­i­cal method.

To do this, on a sheet of graph paper placed over the sketch-project of the house, the loca­tion of the heat­ing cir­cuit is marked in accor­dance with the fol­low­ing rules and reg­u­la­tions:

  • The length of the pipe in the heat­ing cir­cuit must not exceed 120 m. At the same time, there should be no joints and breaks at its out­let from the pres­sure man­i­fold and the inlet to the return line.
  • Pipes in the con­tour spi­ral should be locat­ed in incre­ments of 10–15 cm.
  • The thick­ness of the screed must match the diam­e­ter of the pipe. That is, for a pipeline of 16 mm, the fill lay­er should be 6 cm.

On aver­age, pipe con­sump­tion per 1 sq. m of area is about 5 lin­ear meters with a dis­tance between the turns of 20–30 cm. That is, for a room of 20 square meters. m will need about 100 m of pipes. To facil­i­tate the cal­cu­la­tions, you can use a spe­cial cal­cu­la­tor for cal­cu­lat­ing the under­floor heat­ing on the Inter­net.

The tem­per­a­ture of the coolant in the sys­tem and the speed of its move­ment are deter­mined by the aver­aged val­ues:

  • To warm up the sur­face to the opti­mum 25 — 37 ⁰С, its tem­per­a­ture should be 40–55 ⁰С.
  • In this case, the coolant must move at a speed of 27–30 l / h (for a cir­cuit with a diam­e­ter of 16 mm).

The pipe lay­ing step is deter­mined in accor­dance with the draft. For edge sec­tions, it should be 10 cm, for the rest of the floor sur­face — 15, 20, 25 cm, but not more than 30 cm. For accu­rate cal­cu­la­tions, there is also a pro­gram for cal­cu­lat­ing a warm floor, which can be found on spe­cial­ized sites on the Inter­net.

Pipe laying methods

Hav­ing decid­ed on the num­ber of pipes and their diam­e­ter, you can pro­ceed to the next impor­tant point: choos­ing the method of lay­ing them.


It is used in rooms with inter­nal walls, with an insu­lat­ed out­er wall. From a hydraulic point of view, this method is the most eco­nom­i­cal. The main dis­ad­van­tage of this lay­out is the large tem­per­a­ture dif­fer­ence at the start and end points of the pipeline. This is due to the fact that hot water is sup­plied from one side, that is, at the end of the room, the cooled coolant will move to the return line, and the tem­per­a­ture there will be low­er.

In addi­tion, this option for lay­ing pipes is quite labo­ri­ous. Quite often it is made with a pipe pitch of 20 cm or more due to the fact that it is very dif­fi­cult to bend them for a small­er pitch, espe­cial­ly when it comes to a pipe with a diam­e­ter of 18–20 mm. It is most ratio­nal to use such an arrange­ment of pipes in san­i­tary areas where it is nec­es­sary to bypass plumb­ing fix­tures and devices, as well as to align adja­cent areas of heat­ing cir­cuits.

water floor installation methods


This method has the same draw­back as the pre­vi­ous one: uneven heat­ing at dif­fer­ent points in the room. There­fore, when using it, pump­ing units of increased pow­er are need­ed, pump­ing water in the sys­tem at high speed.

Spiral or snail

With this method, the lay­out of pipes is made from the perime­ter of the room to the cen­ter. Thus, uni­form heat­ing of the entire sur­face is achieved, which makes the oper­a­tion of the warm floor as con­ve­nient and com­fort­able as pos­si­ble. When lay­ing in a spi­ral, pipes can be laid out on sur­faces with any step, start­ing from 10 cm. This method is suit­able for premis­es of any pur­pose and area.

Additional work

For your floor to per­form at its best, it is nec­es­sary to ensure its thor­ough ther­mal insu­la­tion, since, in its absence, heat loss can be 15–20% . To cre­ate a heat-insu­lat­ing lay­er, the fol­low­ing mate­ri­als are used:

  • Min­er­al wool.
  • Foam con­crete.
  • Glass wool.
  • Tech­ni­cal traf­fic jam.
  • Sty­ro­foam.

If there is an unheat­ed room under the base of the floor, the thick­ness of the ther­mal insu­la­tion lay­er should be 20–25 cm.

Recent­ly, spe­cial mats for ther­mal insu­la­tion have become wide­spread, which are plates with a min­i­mum den­si­ty of at least 25 kg / m3. Thanks to their use, heat dur­ing heat­ing spreads in the “right” direc­tion: from bot­tom to top. The most pop­u­lar type of prod­ucts of this type are poly­styrene foam mats made by hydropel­lent stamp­ing.

Them pros:

  • high den­si­ty (40 kg/m3).
  • The pres­ence of an upper relief struc­turein which it is con­ve­nient to mount pipes with a diam­e­ter of 18 mm.
  • Ease of instal­la­tion due to the pres­ence of a lock con­nec­tion, as in a lam­i­nate.
  • Excel­lent ther­mal and sound insu­la­tion qual­i­ties.

Pri­or to instal­la­tion, the cost of a warm floor is also cal­cu­lat­ed, which makes it pos­si­ble to esti­mate the amount of finan­cial costs for the entire range of works on the instal­la­tion of a water or elec­tric heat­ing sys­tem.

Thus, in order for under­floor heat­ing to per­form its func­tions to the fullest and work effi­cient­ly and eco­nom­i­cal­ly, it is nec­es­sary to draw up appro­pri­ate projects and make the nec­es­sary cal­cu­la­tions.

This work can be entrust­ed to qual­i­fied spe­cial­ists who will be engaged in the fur­ther instal­la­tion of the heat­ing sys­tem or per­form it on their own by cal­cu­lat­ing the warm water floor using an online cal­cu­la­tor.

In any case, well-made cal­cu­la­tions will save a lot of mon­ey that will have to be spent on the future oper­a­tion of under­floor heat­ing, and will sig­nif­i­cant­ly increase their ener­gy effi­cien­cy.

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