Accumulation heating, heating cables every 8 or 16 cm?

The correct choice of heating power determines the efficiency of the entire system, and thus the comfort of the residents. Too much spacing between heating cables can prevent optimal heat levels, leading to cooler zones in the floor.

How densely to lay the heating cable?

• Below are two real simulations of the installation of electric heating of a concrete slab 15 cm thick.
• Both use the same 10 W/m heating cable, but at first it will be spaced every 16 cm, while in the second case it will be spaced every 8 cm.

Heating cable installed every 16 cm

A 10 W/m heating cable was installed in the foundation slab at 16 cm intervals. Then an analysis of the temperature distribution on the surface of the slab was performed. What were the conclusions of the observations?

Temperature distribution with heating wires spaced every 16 cm.

In the diagram you can see green bars - this is the trace of the heating wires located. In these places, the temperature reaches above 28°C. Due to the large distances, the space between the wires has not heated up sufficiently, even reaching below 25°C. As a result, the heat accumulated in this way will not be able to heat the house.

Side cross-section of the foundation slab with the heating cable spaced every 16 cm.

The situation in question is even more apparent in the side cross-section. You can clearly see the separated locations of the heating cable. However, the heat generated is not able to heat the large space between the wires.

Heating wire installed every 8 cm

In the same 15 cm thick concrete slab, the same 10 W/m heating cables were installed, but at twice the spacing. This resulted in a completely different temperature distribution diagram:

Temperature distribution with heating wires spaced every 8 cm.

It is worth noting that by reducing the distances between successive heating cables twice, twice the heating power in a given area was obtained. As a result, the temperatures achieved are much higher. The temperature graph is also flatter, indicating a uniform temperature distribution with only the edges of the foundation slab missing. What does it look like in side cross-section?

Side cross-section of the foundation slab with the heating cable spaced every 8 cm.

It can be seen that the temperature distribution is much more uniform. At the same time, it can be seen that the temperature of the entire pyre is much higher, reaching more than 40°C. This means that much more heat energy has been accommodated in the concrete screed, which can now be used to heat the house for the rest of the day.

Conclusions from the analysis of electric heating of the foundation slab

Comparing the two cases, it is worth remembering that with a distance of 8 cm between successive heating cables, twice as much cable was used. However, the effects can be perfectly seen in the posted graphics. In the first case, the heating time is significantly extended so that the board can accumulate sufficient heat energy. The temperature reached reaches a maximum of 29.4°C. This means that the electric underfloor heating will have to be restarted to reheat the building.

By using more heating cables, a much higher floor slab temperature (36.13°C) was achieved. Although more electricity was needed to heat the concrete, the accumulated heat is enough to provide comfortable conditions for the whole day. At the same time, heating the floor to the desired level was much faster.

Although it may seem that increasing the heating power of the system will mean more electricity consumption, in general it is exactly the opposite. Faster achievement of the optimal level of heat and longer maintenance of high temperature by the heating question, allows the use of a cheaper tariff or domestic photovoltaic installation. As a result, heating bills will be much smaller, and comfort in the apartment - incomparably greater!

• Read also: Accumulation heating in the foundation slab - 10 or 20 W wire?