How To Install Underfloor Heating On Concrete Floor

Underfloor heating is a much more efficient and effective way of heating the home because heat spreads out evenly in all directions, heating the room space from the bottom up. Underfloor heating is also very versatile as it can be installed below many different surfaces including stone, wood, laminate and carpet. It can also be installed on top of an existing concrete floor. The main benefit of underfloor heating, when compared to radiators is lower energy bills as less heat is wasted.

In this guide, we look at how to install underfloor heating on concrete floor with comparisons of both electric and wet system installations. Laying underfloor heating on concrete floor is ideal for retrofitting older properties with existing concrete floors. With this method, there is no need for the existing concrete to be broken up and removed or for any new concrete to be laid.

Preparation for installing your underfloor heating on concrete floor

Before you can install underfloor heating on a concrete floor there are a few important preparation tasks that need to be carried out. It’s a good idea to check the different options for your underfloor heating system so that you can effectively plan how it is all going to be installed, how long it will take and what it will cost. Underfloor heating on concrete floors can be installed by anyone who has the knowledge and skills associated with electrical work and plumbing. Otherwise, it’s a job for a professional underfloor heating installer.

In preparation, you should first ensure your home is fully insulated and that includes window, wall and loft insulation. Draughty windows and inadequate insulation will defeat the object of saving money on energy bills. Without adequate insulation, your underfloor heating will not be as efficient as expected because heat will escape through walls and gaps around windows and also through the roof of the property if there is insufficient loft insulation.

Before considering the installation of underfloor heating on concrete floor, ensure the existing concrete floor is sound and free from cracks. It also needs to be level and ideally, have a smooth finish. If it is breaking up it will need to be replaced or repaired. Clean the floor surface thoroughly by removing any dust and dirt and ensure the surface is dry and free of grease. Also, before you start, check that you have all the necessary components for completing the job. If in any doubt then call in a professional underfloor heating specialist to do the job.

Prepare the flooring

There are 2 different types of underfloor heating systems to choose from, water underfloor heating and electric underfloor heating, the latter being the easier and quicker option. There are also variations of wet underfloor heating system installations. Here, we will look at the typical installation of a water system or wet system installation as it is usually known. First, ensure the skirting boards and doors to the room have been removed. These will need to be altered before being replaced to take into account the new, higher floor level. Prior to laying any pipework, insulation boards will need to be laid over the concrete floor.

Cut the boards

For both electric and water underfloor heating systems, insulation boards must be laid to the floor surface, ensuring they fit right up tight against the internal walls. Insulation boards are usually made from polystyrene or polyurethane which can be trimmed easily with a sharp knife. Any gaps between the boards can be taped using insulating board tape. Without insulation boards, most of the heat will be absorbed by the concrete floor below with little heat reaching the surface level.

Fitting the perimeter strip

When installing underfloor heating on an existing concrete floor, you will need to apply an edging strip, also known as a perimeter strip to the edges of the floor space. A perimeter strip is a type of insulation that fits around the edges of the walls. It should cover the full depth of the installation including the final screed. The perimeter strip allows for expansion and acts as a thermal barrier, preventing heat loss from the floor through the walls. It also ensures there is no significant movement of the insulation boards at the edges when the screed is applied. As a final screed of sand and cement is going to cover and hold all the pipework in place it is recommended that a plastic slip membrane be placed over the insulation boards.

Check the pipe layout drawing

With wet underfloor heating on an existing concrete floor, it is highly advisable to work on a pipe layout drawing that has been previously designed for your particular installation. Fee CAD designs can be provided by the suppliers of the UFH kit or if you are able, you could design the layout yourself. A design is essential if you want to achieve maximum efficiency with a minimum of waste. It will also make the installation process much easier and quicker.

With electric underfloor heating, the heating wires are already attached to mats, which can simply be rolled out over the floor surface. A wet underfloor heating system requires more work including laying the water pipes at the appropriate spacing, which is typically around 150mm to 250mm depending on the type of heat source. For example, for standard rooms, the pipe spacing is usually 250mm. For rooms with high heat loss such as conservatories, the spacing is best set at 200mm. If the heat source is from an air or ground source heat pump then 150mm spacing is generally best.

When laying the pipework, ensure no pipes are situated below permanent fixtures or fittings such as baths, sink units, cookers or kitchen cabinets. Allow a space of at least 100 mm from the base of walls and doorways.

Installing underfloor heating on concrete floors

Once the insulation has been fitted, the perimeter strip put in place and the pipes laid out, it is time to move to the next stage. Ensure the pipework is held firmly in place by staples which can be pushed easily into the insulation boards at 1-metre intervals. The next stage involves connecting the pipework to the manifold. Mark each pipe with a flow number and a return number for each loop. Each pipe will begin and end at this pump and manifold component. This is the control area where each pipe is connected via valves to control flow levels. More information can be found in our guides and installation manuals.

Floating screed

When all the pipework has been connected to the manifold, the system should be pressure tested to ensure there are no leaks. It is best to leave the system running for a short time while you check the whole length of pipework and the connections for any sign of leakage. If all is well, then the next stage is to cover the pipework with screed. A screed is a mix of sharp sand and cement and for this purpose, the screed you will use is known as floating screed. This is mixed at a ratio of 1 part cement to 4 parts sharp sand. The floating screed acts as both an insulator and as a supporting material for the final floorcovering.

It’s best to plan this part of the job so that you have ample time to cover the complete installation of pipework with screed in one session rather than do small areas at a time. A floating screed mix for underfloor heating on concrete floor, where the concrete floor is now the sub-base should be 65 mm-75 mm thick. Before the screed is mixed and laid, the pipework should be kept at a 6-bar pressure while the screed is laid.

Mix the dry screed mix with water and plasticiser, which will help make the screed more workable. Take care not to step on the pipework as you apply the screed over the top. Work the screed between the pipes with a finishing trowel ensuring each section of pipe is adequately covered to the same depth.

Use a wooden batten or some other straight edge to level the screed before tamping down and levelling with the trowel. Ideally, you want to end up with a smooth and even finish. If for any reason you have been unable to get the screed level, you can add a thin layer of levelling compound. Next, you will need to leave the screed to cure. Normally it can take up to 48 hours to set but as long as 100 days to fully dry and be ready for the final surface covering. However, an accelerator can be used to speed up drying time but check with the supplier that this is suitable for the job in hand.

Floor coverings

When the floor screed surface has fully cured you can lay your desired finished covering. Ceramic and stone tiles are considered the best option because they offer very high thermal conductivity, which is ideal for underfloor heating systems. However polished screed and resin are also popular for the same reason. Linoleum, vinyl, solid and engineered wood are considered to have a high heat transfer level whereas carpets and rugs are rated medium conductivity.

Should you have any questions about any aspect of laying underfloor heating on a concrete floor then contact a member of our professional installation team for advice. Further help, information and advice can be found on our knowledge hub page.