While it was British engineer Oscar Faber who is credited with developing the idea of using hot water pipes to heat buildings in the 1930s, the concept of underfloor heating goes back much further - to 5,000 BC.
Wet underfloor heating is one of the two main types of underfloor heating system available to homeowners.
From comfort to energy efficiency, quiet operation, even heat distribution and improving air quality, there are numerous benefits of wet underfloor heating. But how should such a system be installed?
This guide covers the key stages of installing hydronic underfloor heating, explains how this type of heating works, and offers advice on purchasing a system.
What is wet underfloor heating?
Wet underfloor heating is also known as hot water or hydronic underfloor heating. This type of central heating system uses pipes to distribute hot water through the floor of a room or building.
Due to the even heat distribution facilitated by hot water underfloor heating, residents can enjoy more consistent and comfortable heat at home. Rooms with traditional radiator heating may have hot and cold spots, depending on where the radiators are placed.
Hydronic underfloor systems heat up the room from the floor upwards, including the people and objects in it.
How does wet underfloor heating work?
Wet underfloor heating circulates hot water through a pipe network beneath the floor.
The water is heated by a heat pump or boiler to a specific temperature dictated by the setting chosen on the thermostat. It is then pushed through the pipes by a pump manifold.
The heat from the water is transferred to the floor above, which heats the room evenly to create a comfortable environment. Pipes are typically made of tough materials such as PEX, a type of polyethylene.
Today’s wet underfloor heating systems allow you to heat various areas of your home independently. This zonal functionality means that you can control the temperature in each room at any given time, depending on your preferences.
Wet underfloor heating provides benefits such as comfort, energy efficiency and even heat distribution, as well as a low operating noise compared to forced air heating systems; heating, ventilation and air conditioning (HVAC) systems, for example.
Installing wet underfloor heating
Wet or hydronic underfloor heating is recognised as being more complex to install than electric underfloor heating systems. If you aren’t experienced in this area, it usually makes sense to leave the project in the hands of an accredited professional installer.
Below, we will outline the key steps in wet underfloor heating system installation:
Preparing the subfloor
Unless your home is in the process of being constructed, you will need to remove the existing flooring so that you can gain access to the subfloor.
It should be clean, free from dust and debris, and clear of any obstacles that may impede the installation process.
Levelling the subfloor
While you have access to the subfloor, you should ensure that it is as level as possible.
This will give you the basis for even heat distribution throughout the room when the system is up and running. Small dips or peaks don’t matter too much, but you should be sure to sand noticeably raised areas and rectify big dips using a self-levelling compound.
Installing insulation foam
Installing insulation around the perimeter of a room will improve the efficiency of an underfloor heating system, helping to prevent heat from escaping and boosting performance. The material does this by providing thermal resistance.
Common types of insulation for this purpose include foam panels, rock wool and reflective foil. The insulation material is cut to fit the dimensions of the room and laid underneath where the pipes will be located.
Installing the concrete substrate
Most hydronic underfloor heating systems are laid on top or embedded within a concrete substrate. The concrete substrate is measured according to the dimensions of the room and cut to size. It will provide a solid base for the underfloor heating system and will be another element that is integral to even heat distribution.
Before going any further, check that the substrate is clean and level.
Installing the boiler and manifold
A professional installer will set up the boiler and pump manifold.
The boiler performs the function of heating the water, while the pump manifold acts as the central hub of the underfloor heating system, distributing hot water to the network of pipes around your home. Given its role, the manifold is usually best located near the boiler in a central location.
The boiler is connected to the manifold with PEX tubing, and your technician will ensure that all connections are secure and tight.
Laying the pipes
Your system will have been designed and planned in line with the size of the area you wish to heat, and other factors such as the location of the boiler and manifold. Obstacles like furniture and other utilities will also be considered.
Once the boiler and manifold have been installed, the PEX tubing pipes can now be laid. The tubing will be unrolled and laid out in a ‘serpentine’ pattern - that is, a curved pattern with U-turns that resembles the shape of a snake. The rows of tubing will be evenly placed for optimum heat distribution and can be secured using clips.
Once the pipes are in place, they can be connected to the manifold, before the connections are checked again to ensure there are no leaks.
Filling and pressurising the system
Before it can be tested, the system will need to be filled with water.
Air can be bled out of the system by opening the manifold’s air bleed valves. Once the system is filled with water, a pressure gauge is typically used to pressurise the system. This will be set according to the pressure recommended by the manufacturer of the system.
Install the thermostat
The thermostat should be installed near to the underfloor heating system, but away from direct heat sources.
The thermostat is mounted securely to the wall and wired into the hydronic heating system. Probes that measure the temperature of the floor are installed beneath the floor to give an accurate temperature reading.
Once mounted and wired into the system, the thermostat can be programmed to specific temperature settings, automatically adjusting the hot water flow to maintain a certain temperature.
Testing the system
Now the system has been filled and pressurised, it can be tested.
Testing will ensure that the system is working properly and is ready for use. After turning on the boiler and circulation pump, the desired temperature will be chosen at the thermostat.
Testing will allow a professional installer to identify and address any leaks in the system, and listen for unusual noises that suggest an issue. The system is usually turned on for a few hours to ensure that it heats up the space adequately and evenly.
Wet underfloor heating buying tips
While the installation process can be taken care of by a professional service, there are some important decisions to be made by you as a buyer of a hydronic underfloor heating system. We’ll conclude this guide with some useful tips and factors to consider when purchasing a system:
Choose the right system for size
The size of the room or area within your home that you want heated is essential.
Firstly, those with larger homes may opt for wet rather than electric systems, as they generally offer more efficiency over a bigger area.
Then, the size of the area to be heated and heat loss calculations - such as how many windows there are in a building, how well a space is insulated and weather patterns at the location - will be taken into account.
Due to the number of variables involved in these calculations, it is recommended that you consult with a professional installer who can guide you on the right size system, explaining how they have come to a sizing decision. This is an important consideration that will allow you to install a system capable of meeting your needs.
Considering the heat source
You may choose between several options for heating your wet underfloor system.
These include boilers and heat pumps, as well as renewable energy systems such as geothermal or solar.
Boilers - which can provide consistent and reliable heat and are fairly inexpensive to install - are the most common choice. Heat pumps are recognised as more energy efficient and generally better for the environment, but their installation costs are typically more than boilers.
Renewable energy sources that utilise the sun or earth’s heat have grown in popularity, and are both sustainable and efficient. However, their feasibility in terms of logistics and cost can depend on their location.
Shop around and check warranty length
Installing wet underfloor heating is more complex than installation for electric systems.
For this reason, it is even more important to select an experienced, trusted professional to oversee and execute the installation process.
Be sure to collect quotes from several contractors before you come to a final decision, asking for testimonials and details of their experience. Factoring in the cost of installation into your overall spend for the project is also important, ensuring that you don’t go over your budget.
Finally, look carefully at the warranty offered by a manufacturer. While the best hydronic systems can last for decades if well maintained, a long warranty can give you reassurance that your investment is protected in the long run.
That’s a wrap on our wet underfloor heating installation guide. Remember, a professional installation job can ensure that no unforeseen issues pop up further down the line, and leave you to enjoy a comfortable, efficiently heated home.