1. By hot water
In this case the system is similar to a hot water heating system, with a boiler "Boiler (heating)") or other heating means, and a distribution network, but with the floor as emitter (or as has been said, another surface, although in hot water systems it is rare to find it), under which a pipe runs making meanders, so that the tubes are at a relatively short distance (between 8 and 30 cm).
The water pipes (generally made of plastic material) are distributed over the floor (see image), interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") made of cement or anhydrite and sand with a minimum thickness of 4 cm and a maximum of 6 cm is placed on the pipes. Then the flooring, which is recommended to be made of a poorly insulating material from heat (stone, ceramic or hydraulic tile) and not wood or carpet.[note 1] The unpleasant contact of the sole of the foot with a cold material, which we normally want to avoid with these thermal insulating floors, is compensated by the temperature of the floor.
If the building is well insulated, it is not necessary to cover the entire surface of the floor and you can leave some narrow strips, close to the walls, without pipes, to place furniture (shelves, sideboards,...) because under them the floor will not emit heat that could damage them.
Given the limitation of the ground surface temperature, in this case only regulation can be made by the heat transfer temperature (proportional regulation) which normally should not exceed 50-55 °C.[note 2] The system consists of a control unit that receives information from two temperature probes. One of the probes informs the control unit of the outside temperature, and depending on it, the control unit moves a motorized multi-way valve, mixing the water from the boiler with cooled return water, until the appropriate temperature of the water supplied to the network is achieved, according to the corresponding heating curve, at each moment, a temperature of which the other probe, located right at the beginning of the delivery pipe, informs the control unit.
It must be taken into account that the maximum soil temperature (the 28 or 29 °C mentioned) will only be needed in the coldest times of the year; the rest of the time (with lower heat needs), the emission must be done at a lower temperature, then the heat transfer temperature will also be lower.
This heating system also has a kind of natural self-regulation: as the ambient temperature rises (due to occupancy of many people, for example), the emitter-ambient thermal jump decreases, so the heat emission decreases, the heat carrier cools less and returns to the boiler hotter, reducing its work and saving fuel. As the surface-environment thermal jump is low (of the order of about 10 °C in the coldest times), an increase of 1 °C in the environment represents a 10% decrease in the emission on those coldest days. The truth is that the same thing happens to water systems and radiators at higher temperatures, but, as the thermal jump is much greater (50-60 °C), the savings are negligible (1-2%).
2. By electricity
There are also radiant wall systems that work by electricity. There are basically two ways to do it:
The electrical resistances are distributed over the floor,[note 3] interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") of cement and sand is placed on the resistors, and then the screed. Regarding the material of the flooring, see above what was said for the system with water pipes.
The carbon fiber system consists of a kind of weaving of these fibers, which function as resistance, in bands of a certain length, which have two electrical conductors on the sides and all wrapped in a sheath of flexible plastic material (as an electrical insulator). As has been said, in many countries it is prohibited to use anything under electrical voltage under the flooring (unless they are armored electrical resistance), so in those countries it is used on the ceiling: on a false ceiling of plaster or plasterboard, the sheet is placed and on top of it a fiberglass blanket insulator, so that the heat is directed exclusively to the heated room.[note 4].
In this case the regulation cannot be done by temperature of the emitter, but by time. It is regulated by a thermostat that cuts off the current of the resistors when the desired temperature is reached in the room; The lower the needs (depending on the outside temperature), the shorter the ignition time. It has the advantage that the regulation is done local by local, so that in the unused ones you can set a lower temperature, or even turn them off. The disadvantage is that the soil can reach the maximum temperature all season, even for short periods of time.
A more economical possibility is to use a system of water tubes, heated by a heat pump using electricity. In this case it would be an air-water pump (or water-water, if there is a possibility of having a suitable cold source) and then the installation would be through pipes, as in the previous case.