Underfloor heating is an effective and reliable method of heating your home. These systems are either water or electricity based. The water system (wet underfloor heating) uses hot water from your boiler, while the electric one (dry underfloor heating) uses electricity. Wet systems are relatively more efficient and have lower running costs. They can also be used for cooling your floors, unlike dry systems, which can only be used for heating. These systems can be used for heating a single room with your central heating system or on a stand-alone basis for heating your entire home.

What is Included in an Underfloor Heating System?

A wet underfloor heating system uses fine water pipes attached in a series to each other. The system draws hot water from your boiler, which passes through these pipes and, through heat exchange, heats your floor. The hot floor transfers this heat to the air in your room, and the process continues till you have heated your room to the desired temperature. The cold water is recycled back to your boiler. The dry system uses electric cables instead of water pipes, while the rest of the process is the same.

Installing UFH Systems Underneath Screed

The first step in underfloor heating system installation is cleaning. The subfloor, which is typically concrete, is first cleaned thoroughly. This is done to avoid any damage to the pipes or cables. A damp-proof membrane is then installed over the entire floor. This helps in protecting the pipes from corrosion. Next to follow is insulation. Thermal insulation sheets, usually made from mineral wool or polystyrene, are evenly spread over the waterproof membrane. Insulation plays a vital role in defining the efficiency of an underfloor heating system. We shall come back to this later. Once the insulation is in place, it is time to install the manifold and the heating pipes. The manifold should be installed first and is usually hung on a strong wall which can withstand its weight and ensure a perfect fit. The pipes are then connected to the manifold’s flow side, usually marked by an arrow. After the manifold is installed and the pipes are attached, the pipes are laid on the floor. It has to be ensured that the spacing between the pipes and their layout is accurate for uniform heating. Clips are used to join the pipes with the underlay. This is done to ensure no free movement of the entire assembly. Once all this assembly has been installed, a pressure test is carried out to check for any leakages. If everything is perfect, the technician will move to the final step, which is the application of liquid or dry screed.

What is Screed?

Screed is a cement-like mixture of aggregates and is used for surfacing. In other words, screed creates a smooth and uniform layer over concrete surfaces. Screed is either liquid or dry. Dry screed typically comprises large-size aggregates, while liquid screed has small aggregates. Both are highly effective, but liquid screed is quicker to dry and is also considered more effective when it comes to the smoothness of the top layer.

  • Traditional or Dry Floor Screed

Traditional or dry screeds are a mix of large-size and coarse aggregates such as sand and cement. The composition of screeds may vary from contractor to contractor. These aggregates are mixed in sufficient water to get the right consistency. The drying times of traditional screeds range from 5 to 7 days, while complete curing may require up to 30 days. If you have applied screed with your underfloor heating system, you can turn on the heating after 28 to 30 days. Even then, the heating has to be kept low for a few days to cure the dry screed effectively.

  • Liquid Screed

Liquid screeds are often called “flowing screeds”. They are quick to dry and are considered more efficient than dry screeds. It has smaller aggregates and can easily be poured or pumped where needed. Once applied, the mixture hardens by itself and creates a flat & smooth surface. Some liquid screeds are self-levelling, implying that you don’t need to level them. They do that automatically. The drying time of liquid screed is 24-48 hours, much lower than dry screeds. However, with underfloor heating, the total cure time may be longer than dry screeds.

Once completely cured, it is more efficient than a dry screed.

  • Screed Depth and Underfloor Heating

Screed should be applied according to its recommended thickness. Anything above and below the recommended thickness will affect your underfloor heating system. While the application is simple, and you can do it yourself, we highly recommend hiring professionals to do the job. Ideally, dry screed thickness should range between 65 to 75mm, and the layer should be uniform throughout the surface. Liquid screed is much thinner, and the thickness can go as low as 50mm, leaving more space for insulation and thus increasing the thermal efficiency of your heating system.

How to Prevent Underfloor Heating & Screed Issues

Keep the following tips in mind to get the most out of your underfloor heating system and screed application.

  • Consider the size and shape of your room when selecting the capacity and layout of your underfloor heating system.
  • The piping layout should promote the free flow of water and should not have any sharp bends.
  • Underfloor heating systems behave differently with different flooring materials. The interface temperature (between the flooring and the subfloor) should not exceed 27°C.
  • Insulation plays a vital role in enhancing the efficiency of your heating system and should include manifold assembly and the primary pipework.
  • Floor insulation sheets play a vital role in preventing heat loss.
  • The manifold should be within easy reach and installed on a strong wall.
  • Correct labels on your underfloor heating system components will make repairs and replacements easy in the future.
  • For ease of maintenance, Joints between pipes and the manifold should be kept above the screed level.
  • To protect your underfloor heating system from frost, you should ensure that all windows and external doors are installed before installing the heating system.
  • The layout of the underfloor heating piping should ideally be in accordance with the supplier’s instructions.
  • The spacing between the pipes should be the same unless the shape of the floor demands narrowing it down at some locations.

DIY vs Professional installation

You will find many instructional videos on the internet for installing underfloor heating systems and applying screed. However, if you have no experience, hiring professionals to do these jobs is preferable. Underfloor heating systems need perfection to provide you with their benefits. Any flaws in installing the system or its accessories will be hard to resolve once the screed has been applied. You will end up wasting money instead of saving it. Professional fitters and installers with adequate experience will ensure that the heating system is installed in the best possible layout and the remaining accessories, such as insulation, waterproof membranes, manifolds, etc., are installed with perfection. Professional screed application will ensure that you have a smooth surface to install your flooring and also enhance the efficiency of your heating system.