As part of your underfloor heating system, we have supplied you with Heatmiser PRT digital room thermostats. When the system is running, make sure that the room thermostats are set at 20°c, the system is designed to work at 20 to 21°c – which is an appropriate indoor temperature for the UK. The pump speed should be set to speed 3. The mixing valve is normally set to 45°c for concrete floors and 55°c for timber suspended floors. If for some reason the rooms aren’t heating up, the flow temperature on the mixing valve can be increased.
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If the system is making any noise, then it is possible that air is in the system. The air can be removed from the end caps on the manifolds, similar to a radiator system. Make sure that the system is operated for 24 hours before making any adjustments.
Note, the system should operate 24 hours a day during the heating season, this is the most efficient way to run it. The Heatmiser PRT thermostat comes with set-back, so you can set the room thermostats to drop 5°c at night for example and in the morning the system can respond quickly to return to the required daytime temperature, see instructions provided for the Heatmiser PRT.
Room thermostats are normally fitted 1.5 m from the floor, located near to the light switch. Try to avoid positioning them in direct sunlight as it will affect their readings.
The maximum heat output for a underfloor heating system is 100 W/m2 for concrete floors and 70 W/m2for timber suspended floors. For any underfloor heating system to work efficiently, the property needs to be built to current building regulations. Carpet and underlay together should not exceed 2.5 Tog.
If you are using the underfloor heating for a Conservatory, note that it will extend the time you can use the Conservatory for. It will not keep it at 20°c all year as the heat losses are higher than 100 W/sqm in a Conservatory. This is also generally the case where radiators have been fitted.
Condensing boilers are very efficient used in conjunction with underfloor heating. For combination boilers, it is always recommended to check with the boiler manufacturer whether it can be fitted with a secondary pump.
If the project is a small flat and the combi boiler is only providing underfloor heating and hot water, it is possible to install the system minus the control unit, provided there is a safety device fitted to the boiler to prevent flow temperature getting adjusted above 60°c.
Underfloor heating systems can be mixed with conventional radiator systems. Also note that the underfloor heating system needs to be a complete separate system , ie the flow and return for the underfloor heating needs to go all the way back to the boiler. If you do have radiators in your system, we recommend independent control from the boiler, ie not together with the underfloor heating.
If you are using a heat pump, please make sure that the heat pump company specify a pump that can cope with the underfloor heating duty as you might not need our control packs with heat pumps. Heat pumps should be supplied with a buffer tank (ask your GSHP supplier).
We recommend a minimum of 50mm of Polyurethane insulation for the underfloor heating system. This is very high quality insulation and can be used for both concrete and timber suspended floor constructions.
Note we do not supply the insulation. Any builders’ merchant will have Celotex or Kingspan insulation in stock. The quote is based on clipping the pipe direct to the insulation board. We do supply pipe clips. With concrete floors, we recommend 65mm – 75mm of screed on top of the insulation.
Also 50 mm liquid screed or fibre screed can be used. It is important to fit a plastic membrane on top of the insulation if liquid screed is used. Edging strip must also be used if liquid screed is applied.
The screed must be allowed to dry for a minimum of 4 to 6 weeks before the heating is operated. The first time a system is used, the mixing valve should be set to minimum in order that any moisture in the screed drys out. Following this, the temperature should be increased by two degrees every day until the mixing valve is set at 45°C. Floorboards must have moisture content lower than 7% before they are installed. We do not recommend floorboards thicker than 25mm, see our technical page for more information about floorboards. Always check with the manufacturers of any floor finish that it is compatible with underfloor heating. It is important that no floor finish is laid on the concrete until it is 100% dry.
For stone and ceramic tiles, flexible adhesives and grout are recommended. Avoid carpet underlays of the felt and rubber crumb type. With Vinyl, check with the manufacturer that it works with underfloor heating and laminate flooring should always have an expansion gap, to allow for movement.
As WCs and Bathrooms are generally small areas, extra heat might be needed. Therefore it is standard practice combine towel rails with the underfloor heating in these areas.
If there are metal parts in the system, it should be flushed with Fernox or a similar product. For an average size UK property (4 bed house), 22mm flow and return to the manifold is suitable, larger properties should use 28mm flow and return. We highly recommend that the plumber installs isolating valves before the the pipework is connected to the manifold from the boiler, in case the pump needs servicing or the mixing valve needs cleaning out.
Before the screed is laid the system must be filled with water and fully vented of air. This can be best achieved using mains pressure through the two filling valves at the end of the manifolds. All valves should be closed and the flow filling valve connected with a hose to the mains water supply, with the return filling valve connected to a hose leading to a waste water point.
One by one, the flow and the return valves are opened and closed, purging the loops of air. Ensure that all the black caps on the return manifold are closed. Open the upper ring on the end cap 2 to 3 turns. Open the first black cap and then open the return end cap. Wait until clear water is coming out and make sure that all the air is gone. Close the black cap and do same for the next loop. Continue the process until all the loops are fully vented of all the air. Close the end caps when done.
When this is completed and the filling valves closed off, the pumps should be run for five minutes and the air vented again at the air bleed valve on the filling valves until all air is bled from the system. Do not fill the system from the boiler filling loop.
The system should be pressure tested with 5 bar pressure for 24 hours prior to laying the screed.
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The manifolds are supplied with options for individual control for each room. On the return manifold (the black caps), actuators can be mounted for individual control. If a programmable room thermostat with a two port valve is controlling the system and there is no individual control, the “black caps” should be left open. The flow manifolds are supplied with flow gauges. To adjust the flow gauges, us the key provided with the manifolds. See instructions included in the manifold box on how to adjust the flow meters.
The following is an approximate guide to how far each loop should be adjusted;
Size of Loop Percentage Open
10 – 30 metres 30 % open
40 – 60 metres 50 % open
60 – 90 metres 75 % open
90 – 100 metres 100 % open
Too high or too low room temperature, leaks, cracked tiles - these are only a few possible effects of various types of mistakes made while planning or installing the underfloor heating system. Malfunctioning floor heating is usually the result of careless installation or adopting improper solutions. Today we will look at 10 common mistakes made when installing the underfloor heating system.
The lack of a proper design while installing any heating system may have disastrous effects. In the case of underfloor heating, the layout as well as the shaping of the heating pipes must be adjusted to the parameters of the supply water in the heating system, the screed thickness, the type of floor covering and heat demand. Lack of reliable documentation does not only lead to higher costs of maintenance, but it also spells trouble in case of heating system failure. It is important to document the actual layout of the heating pipes on the room plan, especially in the area between the rooms, under the windows and near the walls. If we know the actual dimensions of the loops, we can avoid damaging them accidentally while installing threshold strips or other elements that require drilling in the floor.
Underfloor heating system must be installed in correct order. It should start after other systems have been laid, otherwise the heating pipes and other elements of the heating system may be damaged. Manifold cabinets and manifolds should be installed before laying the pipes. The floor heating distributor box should be installed as close to the underfloor heating system as possible, rather than in a remote boiler room. It is worth remembering that it is impossible to install the whole underfloor heating system when the house is at the open shell stage without the windows and doors. These elements are necessary to prevent draughts when the screed is setting. Thanks to this, we may prevent excessive drying of the screed surface.
Some problems may also result from poorly executed construction works. Before installing the underfloor heating system, the floor must be prepared properly. What are the most common mistakes which bring about unpleasant consequences? The three most serious ones concerning the the floor preparation are listed below.
Further layers of underfloor heating system such as thermal insulation, heating pipes and concrete screed cannot be laid on uneven surfaces. Careless preparation of the base, skipping the levelling and cleaning stage means that the thermal insulation boards will not adhere well and will not provide a stable support for the screed, which may lead to cracking. In places where the screed cracks, there is a risk that the heating pipes will be damaged. Furthermore, uneven ground requires different thickness of the screed on the floor. That is why it is so important to level the surface before laying the insulation.
Heating pipes form the so-called heating circuit, the length of which should not exceed 100 m depending on the diameter of the pipes used. Therefore, during installation work, make sure that the installer does not make longer heating loops. It is also worth remembering that each loop should be made up of one continuous length of pipe. Connections are allowed in the event of pump damage and with the use of special repair couplings which can be covered with concrete. To avoid problems, it is therefore necessary to select the pipes in such a way as to avoid connections in the places which will be covered with the screed. Such connections are the most vulnerable points because dirt easily deposits there, which results in defects. Failure to follow the instructions will increase the hydraulic resistance, resulting in insufficient heating of certain areas of the floor.
The heating pipes which will carry water must be firmly attached to the ground. First, a special pipe-positioning foil with anchor mesh should be placed on the polystyrene layer. Next, the pipes are secured to the foil using the clips included in the underfloor heating system set. If the pipes are not fastened properly, they can disconnect from the ground while the screed is poured on the ground. In addition, if the system includes copper components, pipes should not be laid directly on concrete as they may corrode. Copper pipes must be protected with an additional layer of plastic. An alternative is to use pipes made of different materials such as plastic or multi-layer pipes. It is worth choosing high-quality products that exclude the risk of damage.
The floor in which the heating pipes are embedded requires proper expansion joints. The heating surface expands due to the heat from the pipes, which is why it is necessary to make expansion joints. If the room is large or has an unusual shape, it is necessary to plan additional expansion joints in the screed. The lack of such gaps or making them only in the floor covering rather than through the screed can lead to scratches and cracks. It is important to arrange the heating pipes in such a way that the expansion joints do not cross them.
One of the last stages of installing the underfloor heating system is to bury the heating pipes in screed. At this stage, it is recommended to supervise the work of people who pour the concrete to avoid damage to the heating pipes or covering the gaps or expansion joints. It is possible to lay the floor covering only after the screed has dried properly and reached its optimum parameters. In order for the concrete to set well, the surface must be prevented from drying excessively. After about 21 days you need to preheat the screed so that the remaining moisture is removed.
Unfortunately, not every material is suitable for covering the floor if we decided to install the underfloor heating system. Therefore, the question of what material will be the best is one of the key questions when it comes to the installation of hydronic underfloor heating. The type of floor covering determines the heating efficiency. For example, a change from ceramic tiles to floor panels will decrease the heating efficiency two times, which in turn will lead to problems with maintaining the pre-set temperature when the outdoor temperature is low. A common solution in this case is to increase the supply temperature, which is not a good solution because it can damage the heating system as well as the floor covering itself. The types of materials used while installing the underfloor heating system are shown in the graphic below.
Before laying the screed, the system must be filled with water in order to check if the pressure in the system has not dropped excessively after a few hours or even a day. At this stage, it is easier to detect and remove leaks than after the pipes have been covered with concrete. The pressure test should be carried out when all heating circuits are filled with water. Sometimes installers give up this activity altogether or fill the pipes with air instead of water. Conducting the pressure test improperly may have serious consequences. It is essential to make sure that there are no leaks before we lay the screed. In the event of an undetected leak, the system can be seriously damaged and repair will be difficult and expensive.
When installing the underfloor heating system, it is a mistake to limit yourself to the simplest solutions and decide not to use controllers for managing the underfloor heating. Neglecting the underfloor heating control leads to significant energy loss, which results from high thermal inertia of the system. Our modern underfloor heating controllers from the 5, 7 or 8 series will allow you to enjoy the advantages of installing this type of heating in your home as well as reasonably manage your home budget.
Read also: Balancing your underfloor heating system as a way to achieve greater thermal comfort and lower heating bills.
Installing underfloor heating is a perfect solution for those who love comfort and convenience. It is worth remembering, however, that only a well-designed and well-made system will ensure the expected results. Mistakes made while laying the underfloor heating system affect the failure rate and reliability of the entire system. By choosing proven solutions, competent contractors and reliable manufacturers, you will be able to enjoy a warm floor for many years.
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