Hydronic Underfloor Heating Overview

What is hydronic floor heating?

Hydronic underfloor heating is an energy efficient and sustainable solution for heating your home. It works well under several different floor surfaces including marble, stone, slate, carpet, timber and all varieties of tiles.

Hydronic underfloor heating is a central heating system and is designed to run continuously during the (winter) heating season. It is not designed for occasional “demand” heating. Where greater heating flexibility is required, particularly for small areas such as bathrooms, en-suites, laundries etc, electric floor heating is recommended.

Hydronic floor heating has become an attractive and regularly specified upgrade for a wide range of applications, especially when paired with a high efficiency condensing natural gas boiler. These systems are quite sophisticated in design and consist of warm water that circulates through an intricate network of polyethylene oxygen-resistant piping under the floor surface. This ensures a gentle, warm heat that is evenly distributed throughout the entire living space.

Hydronic Heating Features & Benefits


Hydronic floor heating is a great option for large, open entertaining areas and it works well under cold floor coverings such as marble, stone, slate, polished concrete and all varieties of tiles.

It’s also fabulous under carpet and timber floors, however you need keep in mind that there are particular standards and temperature restrictions that must be met when using these floor coverings.

The concept of internal repair work. Room with a warm floor and different types of coverage 3d render


These systems require a certain level of maintenance over the years. Boilers require regular servicing and may need to be replaced after 10 years of use. Good quality pipes generally last a very long time (25-year warranty for Rehau pipes).

The overall system is known to exceed thirty to forty years in lifespan. On top of the fairly low running cost, this can give owners a high return on investment when measured against other heating solutions on the market.


Hydronic floor heating can be very economical to run, however, the upfront costs tend to be higher than electric systems, because of the sophistication and intricacy of the design, as well as the skilled labour that is required to perform a proper installation.

A significant part of a hydronic floor heating costs is fixed, meaning it remains similar whatever the size of the area to heat. A gas boiler is an example of a fixed cost that hardly changes when the size of the surface to heat increases. For this reason, the bigger the surface, the cheaper the rate per m2 is. This is an important difference with Electric Floor heating, where the rate per m2 remains the same as the surface to heat increases. This is the reason why hydronic floor heating (HFH) is a more and more interesting proposition than Electric Floor Heating (EFH) as the area to heat increases, and we would recommend to go for HFH over EFH for surface over 60m2.


Another factor in the efficiency of your floor heating system is a high quality thermostat. This will allow you to heat specific rooms independently and program them to meet the needs of your lifestyle.

Because hydronic floor heating is a central heating system, we recommend non-programmable thermostats for your installation. These thermostats can be linked to your home automation systems.

A good quality thermostat will give greater control over temperature, zoning and timing, allowing you to make the most out of your floor heating system.


Installation of a water-based system can be complex due to the intricate design and workings of the system. It is important to seek out a licensed professional to do the job.

Hydronic floor heating systems are normally only used in new projects because it is easier to install into the slab. In some circumstances these systems can be used in retrofit projects, but only in a screed bed that is at least 50 mm in depth (ideally 80mm). As this is a significant height, some customers prefer to go for electric floor heating for renovations.

In hydronic floor heating systems, water is warmed up to 50 degrees Celsius and circulates at a safe, low pressure through a network of pipes, valves, manifolds and switches, all of which must work together to heat the zoned areas:

It is a closed system, which means that the water that is introduced the day the system is commissionned is most likely to be the same for the rest of the life of the hydronic system. For this reason, it is crucial to select the best quality for the manifolds, pipes, boilers and anything that will be in contact with the water, because any inpurity will worsen over time.

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Heating Systems Matrix

Floor Construction Building Type Floor Covering Underfloor Heating type
Electric (heating cables)
In-Slab In-Screed Under-Tile
Hydronic (heating pipes)
In-Slab In-Screed Under-Tile


New Floor Construction
Floating Timber
Battened Timber

Lightweight Suspended

Floating Timber
Battened Timber


Existing Floor Structure
Floating Timber
Battened Timber

× = not appropriate

√ = appropriate

* The space in between the battens needs to be filled with screed

For your perfect underfloor heating solution installation, contact our specialists!

Installation Methods

There are three possible ways to install the hydronic underfloor heating: directly in the slab, in the screed or using diffusion plates.

Hydronic Floor Heating in slab

In-slab hydronic floor heating is the most popular way of installing hydronic floor heating. It is a storage heating system that uses the thermal mass of the slab to store heat. It makes the heating system very slow to respond (it can take one to two days to heat up the slab, depending on the thickness of the slab and the amount of floor insulation used), but is more economical to run, especially with insulation.

Once the slab is heated through, it radiates heat from the floor upwards into the room, creating a comfortable and gently heated environment with no draughts, dust or noise.

We recommend extruded polystyrene insulation beneath the slab and on exposed slab edges to minimise system heat loss and ensure the highest level of energy efficiency and cost savings.

The heating pipe is located on top of the mesh of the slab and requires a minimum of 30mm of concrete cover over the top of the piping. Other options may apply when slab steel reinforcing design will not allow hydronic pipes to be placed over the top steel.

All slabs must be insulated beneath and around the edges of the heated area to prevent downward heat loss and optimise energy and cost savings.

Hydronic Floor Heating in screed

For this configuration, the heating pipes are located onto the top of the finished slab and requires a minimum of 30mm of concrete cover over top of the pipes (therefore a minimum screed depth of 50mm).  This is covered by a suitable floor surfacing such as marble, stone, slate and all varieties of tiles.

This system is generally faster acting than an in slab system. Similar to other systems, it radiates heat from the floor upwards, creating a comfortable, gently heated environment with no draughts, dust or noise.

The heating is controlled using floor or air sensing thermostats that regulate the flow of hot water through the pipe circuits.

We recommend insulation that can be installed on top of the finished slab with the water pipes attached directly to the insulation.

The installer would supply and install the appropriate insulation materials beneath and around the edges to, again, prevent downward heat loss.

Hydronic Floor Heating Timber

Hydronic floor heating can also be used under battened timber floors using diffusion plates. The diffusion plate system consists of aluminium plates with preformed grooves to take the pipe. The aluminium plates transfer the heat away from the pipes giving a uniform heat distribution beneath the timber floor and enabling a more efficient heat transfer to the timber floor. The pipes sit directly beneath the floor boards.

The heating is controlled using floor and air sensing thermostats that adjust the flow rate of hot water through the pipe circuits. The thermostats are typically set to a maximum floor temperature of 27°C to ensure the timber is not over-heated.

Heat Source Options

Hydronic heating keeps running costs down by allowing a choice of energy sources, since the water can be heated by a range of energy efficient and environmentally friendly options.

What heat sources can I use?

  • Gas boilers (Natural Gas or LPG)
  • Electric Heat Pump
  • Geothermal Heat Pump
  • Solar Collectors

Although, gas boilers are typically used, other options include high efficiency electric heat pumps, geothermal heat pumps and solar energy.

We recommend to use a gas boiler with natural gas as a first choice as the up-front cost is much lower than heat pumps while having similar running costs, and it is more reliable than solar collectors. However if your property cannot be connected to natural gas, heat pumps can be an interesting option depending on your budget.

Heat Source Options – Boilers

Devex Systems’ Xboiler range of condensing gas boilers are modern, European made devices that offer a range of benefits to the home owner.  Their advanced design and compact size (740 x 400 x 340 mm) make them suitable for a variety of different locations throughout the home. Thanks to the wide modulation range, the is able to heat with a relatively low heat demand.

The Xboiler can be connected to a domestic hot water tank with a coil via a 3-way valve (pre-installed in the boiler) and controlled with sensor probe.

Technical Features

    • Stainless steel heat exchanger with spacious coil ensures constant water flow over a long cycle reduces debris accumulation
      • ensures constant water flow over a long cycle
      • reduces debris accumulation
    • High efficiency modulating pump with Pulse Width Modulation (PWM)
    • High modulation range: 12% – 100%
    • Weather compensation optional
    • Low level of NOx emission (NOx – Class 5)
    • Modern and easy to use control panel


  • Can be connected to a domestic hot water tank with coil via a 3-way valve (pre-installed in the boiler) and controlled via a sensor probe


  • European Energy Class: A
  • Economic and efficient operation
  • High efficiency condensing boilers with 92% seasonal efficiency and a power output of 20kW or 35kW
  • Small, compact size (785x400x334 mm). Easy to hide inside a cupboard
  • Modulation ratio is 12% to 100% of its maximum output
  • Eco-friendly with very low Nox emissions 14 mg/kWh (BD 25)& 32 mg/kWh – (BD 35)
  • Noise application and insulation offers quiet operation of the boiler
  • Higher efficiency of domestic hot water
  • Higher efficiency circulation pump with automatic airvent
  • Electronically controlled modulating fan
  • Hydraulic group assembled on quick connections
  • Control panel with LCD display
  • Works with domestic hot water cylinders by built-in three-way valve.
  • Better integration with DHW system than standard combi boiler.
  • Complete protection system

Boiler Clearance and Pipe Connections

The boiler should have a clearance of 1300mm underneath, and a clearance of about 100mm on either sides.

The boiler needs to be connected to the gas supply and water supply. The plumber also needs to connect the hydronic system to it, as well as the DHW tank if required. Finally, a drain pipe needs to be connected to get rid of the condensate when the pressure builds up in the tank.

The boiler offers a three way valve for integration with a domestic hot water tank. In normal operation, the valve directs the water into the hydronic heating system. As soon as there is demand for hot water (when someone is taking a shower for example), the valve directs the flow into the DHW tank while cutting the flow to the heating system (the user won’t feel the difference, though, thanks to the thermal mass of the slab). It is a great way to combine your hydronic floor heating system with your DHW system as you only need one boiler for the two.

Hydronic Underfloor Heating – Essentials

Heat Pumps

Heat pumps are an interesting option if there is no natural gas supply to your property. Heat pumps are actually more cost effective to run than gas boilers due to their high efficiency (around 400% for heat pumps versus about 100% for gas boilers). Depending on your location, gas is on average 3 times cheaper than electricity so it makes heat pumps 30% more economical than gas boilers).

However, the upfront cost of heat pumps is usually a killjoy for many customers. On average, you can expect heat pumps to be 6 times more expensive than gas boilers.

Solar Collectors

Not to be mistaken with PV solar panels, solar collectors are tubes in which water is running to collect heat from the sun. This is ideal to use when you have a hydronic floor heating system because you don’t need any expensive energy conversion, contrary to PV solar panels, where a heat pump is necessary to convert electricity to hot water.

Solar collectors are ideally used along with a domestic hot water (DHW) tank so that the heat taken from the sun is used for both the DHW system and the heating system.

Feed Pipes

Feed pipes run from the boiler to the manifolds. They can be installed in different way, depending on your building. They can run under the steel mesh, or through the wall or/and the ceiling. If they are meant to be in the concrete slab or hidden in some other way, we usually use flexible PEX pipes. Otherwise, for visible pipes, we would use copper pipes. Those are more expensive and more time consuming to install, but give a better looking finish.

Feed pipes are insulated to prevent any heat loss. We put the PEX pipe into a conduit to create an air pocket that insulated the feed pipes (using the same principle as double-glazed windows). Or, in the case of copper, we wrap the feed pipes with thick insulation.

We recommend to use a gas boiler with natural gas as a first choice as the up-front cost is much lower than heat pumps while having similar running costs, and it is more reliable than solar collectors. However if your property cannot be connected to natural gas, heat pumps can be an interesting option depending on your budget.

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Manifolds are essentially hubs to which all circuits are connected. The manifolds distribute the water to each circuit and the regulation of the heating is done through actuators that start and stop the flow within the circuits. All actuators are commanded by floor sensing thermostats.

Manifolds can be mounted with a mixing shunt that is used to mix the return cold water with the supply water to decrease the temperature of the supply water temperature. This is used for hybrid system that have both radiators (that work at 80deg Celsius) and floor heating (that needs to work at 50deg Celsius maximum).

Where to install the Manifolds?

Manifolds are best located centrally to the circuits they are feeding and in an accessible location such as the linen cupboards, kitchen islands, laundry cupboards, garage or outside/inside next to boiler. Height and width restraints should always be considered before installation. Manifolds will vary in size according to the number of pipe circuits required.

Manifolds preferably should be situated at the highest point in those circuits connected to it. This means that if you are heating two levels of your home, it is best to have a manifold at each level so that the circuits at each level can be connected into the bottom of the manifolds.

How many Manifolds are needed?

Manifolds can have between 2 to 12 heads. There are as many heads as there are circuits. For 16mm heating pipes,  a circuit can heat around 20m2. Consequently, surfaces of more than 240 m2 will need more than one manifold.

What size of manifold to use?

During the installation you may find yourself with space limitation either horizontally or vertically.

The minimum height required is 600mm. The minimum width is as follows:

Horizontal: If you have limited space horizontally, the minimum height required is 600mm and the minimum width as follows:


Vertical: If you have limited space vertically, the minimum height required is 450mm with the width as follows:

Hydronic Floor Heating Insulation

XPS Insulation

The XPS (Extended Polystyrene) Insulation Sheets from Foamular are designed to be placed directly underneath hydronic floor heating pipes to minimise downward heat loss and aid in faster warm up times.

The standard thickness is 25mm suitable for 16mm hydronic heating pipes and has an R value of 0.89 m2·K/W. Sheets are 2.4 x 0.6m (=1.44m²) for a coverage of 0.70 sheets per m². We also offer 30mm thick sheets (for a R value of 1.07 m2·K/W) and 50mm thick sheets (R = 1.78 m2·K/W).

Quick Heat

The Quick Heat system is ideal for batten timber. It is a combination of diffusion plates and insulation sheets. The insulation sheets are placed directly underneath the aluminium diffusion plates, minimising downwards heat loss.

Hydronic Floor Heating and Solar Energy