We are warmed by the cable: 8 tips for laying cable underfloor heating

Before lay­ing, a ther­mal cal­cu­la­tion of the room is made, heat loss­es are deter­mined, and then, based on the val­ue obtained, a cable of the required pow­er is select­ed. On aver­age, in stan­dard high-rise build­ings with­out insu­la­tion, heat loss is 100 W / sq.m. The cable is select­ed so that exces­sive heat­ing of the floor is not allowed, the sur­face tem­per­a­ture of which should not exceed 30–35 C.

The cable is laid in a screed on a pre­pared (ide­al­ly even) sur­face. A lay­er of heat-reflect­ing mate­r­i­al is laid under the screed, for exam­ple, a lavsan film with a met­al­lized coat­ing. The heat-reflect­ing lay­er does not allow the heat to “leave” down, but not every mate­r­i­al is suit­able for such a lay­er, so it is bet­ter to check with the man­u­fac­tur­ers which mate­r­i­al they rec­om­mend.

Cable design

The screed is usu­al­ly made from a cement-sand mix­ture (wet cement screed), but a dry screed has recent­ly become wide­spread (for exam­ple, from expand­ed clay back­fill). The thick­ness of the screed lay­er above the cable is usu­al­ly made no more than 4–5 cm. Too thin screed will be frag­ile, and too thick will be exces­sive­ly mas­sive. It will slow­ly heat up and cool down just as slow­ly, and this is incon­ve­nient (recall that the main advan­tage of elec­tric heat­ing is a very quick access to the cal­cu­lat­ed heat­ing tem­per­a­ture, a thick screed nul­li­fies this advan­tage).

Make a pre­lim­i­nary cable lay­out dia­gram. The cable should be even­ly placed on the floor, the dis­tance between the indi­vid­ual cable strands (lay­ing step) should not exceed the val­ue spec­i­fied by the man­u­fac­tur­er (usu­al­ly about 20 cm). Too large a lay­ing step leads to the fact that the screed warms up uneven­ly. The cable is attached to the base using plas­tic or met­al clamps. You can also pur­chase a ready-made option — a warm floor based on a mat with a heat­ing cable, in which the cable is already fixed on the basis of their plas­tic mat. Such ready-made kits are much eas­i­er to lay, since you do not have to make sure that the lay­ing step is too large or small, or, say, the bend­ing radius of the cable is too small. The advan­tage of a cable over a mat is greater flex­i­bil­i­ty and vari­abil­i­ty in lay­ing.

Try to deter­mine in advance where fur­ni­ture with low legs (or no legs at all) will be placed — cab­i­nets, beds, etc. The areas of the floor occu­pied by such fur­ni­ture will be iso­lat­ed from the heat exchange between the cement screed and the air in the room. It makes no sense to lay a cable in them.

The heat­ing cable can be resis­tive and self-reg­u­lat­ing. A resis­tive cable heats up even­ly along its entire length, regard­less of the ambi­ent tem­per­a­ture, and a self-reg­u­lat­ing cable is able to respond to this tem­per­a­ture and reduce or increase the inten­si­ty of heat gen­er­a­tion. If a seg­ment of such a cable heats up, then the inten­si­ty of its heat release decreas­es, and vice ver­sa. This is very con­ve­nient, since such a self-reg­u­lat­ing cable will not over­heat if it finds itself in con­di­tions of insuf­fi­cient heat exchange, if, for exam­ple, a cab­i­net is placed on the floor where it is locat­ed or a car­pet is laid. There­fore, if you do not know exact­ly how the fur­ni­ture will be arranged and the car­pets will be laid out, be sure to choose a self-reg­u­lat­ing cable for instal­la­tion.

Do not for­get about floor tem­per­a­ture sen­sors that reg­is­ter the degree of heat­ing of the cement screed and give a com­mand to turn the heat­ing on and off. They should be placed in the screed at the max­i­mum dis­tance from the heat­ing cable threads, exact­ly in the mid­dle between them.

ther­mo­stat

In the process of lay­ing a wet cement screed, it is not allowed to turn on the cable for heat­ing. If you turn on the warm floor until all mor­tars (cement screed or tile adhe­sive) have com­plete­ly hard­ened, then the dry­ing mass will crack.

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