Installation of floor heating

Installation of floor heating


Usually systems of «warm floors» are put in floors of poured concrete. However they may also be placed in wooden floors. There are lot of means of putting «warm floors» but all of them boil down to one: first a warmth insulation with a reflective screen is installed, and then the loops of pipes of «warm floor», and a screed or flooring on top.

The surface of the base must be clean and even; bumps and ridges can be no more than 10 mm. A curved or uneven surface of the base must be leveled with a thin layer of cement-sand mortar or with dry sand. This will prevent damage to the layer of insulation. Before putting the insulation layer you must make sure whether it is recommended for this project of the house, putting steam- or hydro-insulation into the floor construction (for example, the concrete preparation for the floor is made on the ground, or the floor is in the bathroom). If such things are allowed in the project, then steam- or hydro-insulation is put on the base which must be cleaned from dirt. The materials for insulation can be rolled, poured or daubed hydro-insulation materials. If you use materials based on bitumen binding agent as insulation, then before putting heating insulation made of polystyrene foam, the bitumen must be completely dried.

The efficiency of work of the system of floor heating depends mostly on the correct choice of warmth insulation. It is necessary to minimize the heat losses through the floor and through side walls. Polystyrene foam, rigid mineral wool, cork insulation and other types of warmth insulation can be used. For warmth insulation, it is necessary to use materials which reflexive covering or else use special foil. Aluminum foil which doesn’t have a special coating should not be used; the screed mortar has an alkaline environment and will devour the aluminum. This foil is made for steam insulation and is not suitable for laying under a cement-sand screed; but if the screed is made of gypsum binding agent, then foil can be used. The thicker the foil, the better. The point here is that foil acts as a heat spreading element, almost the same as conventional fins. The heated pipes of the «warm floor» give warmth to the foil from their bottom part, and the foil, getting heated, in its turn, gives warmth to the screed, promoting its even heating. Thus the naked foot will not notice a difference in temperatures regardless of whether it is located directly above the pipe or between pipes. Most often ready-made insulation boards are used which have been specifically manufactured for «warm floors» (see Figure 105). While installing insulation boards, it is necessary to ensure that there are no cracks between them and the mortar of the screed will not go between the insulation boards and doesn’t create thermal or acoustic bridges.

The warm floor installed on special warmth insulation
Figure 105. The «warm floor» installed on special warmth insulation

A gap (see Figure 106) must be provided between the walls and the floor in order to prevent the floor, which will expand during heating, from pressing against the walls. For this, before the start of installing the heating system, a strip of insulation with a thickness not less than 5 mm is put along the walls around the perimeter of the room. The height of insulation should not be less than the thickness of the concrete where the heating contour will be. Before pouring the screed of the floor, the strip must be attached to the floor or the wall in such a way that it does not have the opportunity to «float» while the concrete screed is being poured. Such a «float» will cause a breaking of the expansion joint, and this will lead to a rigid attachment of the screed to the wall. As a result, apart from a possible crack formation in the screed, there will be heat losses through the walls and also a transfer of sound waves from the floor to the other constructions of the building. The floor screed must be made in such a way that it will not make contact with the building constructions. It must be fenced with an elastic material from all sides.

Putting of damping strip on the perimeter of the floor of the room
Figure 106. Putting of damping strip on the perimeter of the floor of the room

Loops of the heating contours of «warm floor» must be laid in accordance with the project documentation. Several methods of attaching pipes can be used: putting them into the grooves of insulation (see Figure 105); fastening them by clips to insulation (see Figure 106); or attaching them to the reinforcing wire grid by mounting wire or to a special mounting tape (see Figure 107).

Mounting the pipes of warm floor to the reinforcing wire grid and a special tape
Figure 107. Mounting the pipes of warm floor to the reinforcing wire grid and a special tape

You can also do this in any other way; the main thing is to fix the pipe before pouring concrete. It is recommended that you attach the pipe every 0,5–1 metre. The variant of mounting to the reinforcing wire grid is simple because the reinforcing wire grid is a graphical grid, eliminating time for laying the floor. The grid is made of metal rods with diameter 3–6 mm. The size of the cell is typically 150×150, or less often 225×225, or 300×300 mm. The reinforcing grid allows control the correct placement of the loops of the heating contours. If the grid is put correctly and is a pattern of squares, then the placing of the loops of floor heating on such a surface will not be difficult. An additional advantage to using a reinforcing grid is increasing the mechanical strength of the floor screed due to its reinforcement. Besides, thanks to the grid, the heating pipe will be completely (its entire surface) recessed into the floor screed, guaranteeing maximum heat output. When fastening the pipe to the grid, it is most important not to attach the wire too tightly to the pipe. The wire is thin and with too much tightening, during thermal expansion of the pipes, it will grind against the pipe material. This scenario is unlikely but possible, so it is better to avoid it.

Before installation, determine the order of putting the loops, the route of each of them, from the supply collector to the return one. The heating pipes are marked with a coloured stripe. The stripe serves as a indicator that the pipe was not twisted during installation. It is recommended that the pipe be cut from the roll only after laying the loop and putting it to the return collector. The heating contour must be made of a single piece of pipe or connected with a pressed fitting; pouring concrete on a detachable joint is not allowed. Laying the loop begins with attaching one end of the pipe to the collector. For connecting the end of the pipe to the output of the collector, one should cut it evenly and put a crimp connection on it which consists of a split ring, a crimp nut, and a bushing which should be inserted into the pipe until it stops. The loops must be placed so as to prevent crossing of pipes. After the installation, each loop must have a label near the collector with a designation of the served room or the heating zone.  When laying the pipes of floor heating, it is necessary to remember that hot supply water is being directed to potentially cold areas such as exterior walls, windows and entrance doors.

An example of the internal construction of warm floor
Figure 108. An example of the internal construction of warm floor

After installing the pipes, the heating contour is poured with concrete (see Figure 108). Before pouring, a hydraulic pressure test of the system must be done under pressure of 6 bar for 24 hours. The minimum temperature conditions of installation is 15 degrees C. After the pipes have been installed it is necessary to fill them with warmth carrier and heat to approximately half of the operation temperature. Under pressure and temperature the shape of the pipeline will be determined and only after that can you start installing the final layers of the floor. The pipes of the floor heating, while pouring the concrete, should be kept under working pressure. This eliminates the possibility of further undesirable stresses in the system. Under no circumstances should you send the warmth carrier to the floor heating system with its design temperature until the moment of final hardening of the concrete screed because local overheating of the concrete screed promotes the formation of cracks. After making the concrete screed, you should not send hot water through the system for three weeks. During this time the screed must harden in a natural way and gain the required strength. After this time you can send warmth carrier with 25 degrees C and in the next four days, it should be gradually raised to the design value.

The screed receives the load and distributes it to the softer underlying layer of heat insulation. Therefore the screed must be stiff enough but be as thin as possible in order not to waste extra warmth. Usually the minimum thickness of the layer above the pipes is 40–50 mm and the total thickness reaches 65–70 mm — that is enough to withstand loads up to 200 kg/m². To make the concrete screed, it is better to use «hard» concrete because excessive water content can cause shrinkage cracks.