What is Underfloor Heating?

Underfloor heating uses a pipe or wire network, of either water or electrical systems to heat the floor. Underfloor heating is considered to offer improved energy efficiency, improved comfort and better interior choices than a standard radiator system.

While a radiator will circulate heat, it is often inefficient, with the highest temperature being at the ceiling, and the cooler temperature being at the floor (closer to occupant level). The air circulation contributes to ventilation losses and results in higher fuel costs. Radiators require high temperature water flow due to the small surface available to be heated. Rooms heated with radiators can also experience cold spots due to the heating being in one area of the room.

Underfloor heating creates a more stable and consistent temperature, with a lower energy consumption. Warm water is pumped through the underfloor heating tubes within the floor, and emits the heat across the whole surface heating the room effectively. A lower water temperature is required (around 40C) due to the higher surface area of the heating system (radiators normally operate at around 65C).

image credit: Warmup

Energy

Underfloor heating systems require a lower temperature to operate which results in lower energy requirements for the system (especially the water based systems).

Control

Smart thermostat systems allow control over individual zones or spaces, meaning different zones can be set to different temperatures, or turned off completely when specific parts of the building are not in use.

Position of the system

For a solid concrete floor the insulation position is important, in terms of exposing thermal mass of the concrete to the heat from the pipes, or isolating the concrete/thermal mass from the heat.

Systems which require a 24 hour heating cycle, exposing the concrete slab to the heat from the heating system will allow for a more even heating regime. These systems present a slower response time to alteration requirements in temperature, due to the thermal mass of the concrete.

When using an intermittent heating application, where a faster response time is required for temperature changes, it is more prudent to have less thermal mass available to absorb the heat, and instead place the insulation layer below the screed or timber floor, but above the concrete slab.

It is important the building type, client brief and heating requirements are thoroughly considered prior to selecting the underfloor heating system and flooring type in order to provide the best solution.

Water vs Electric Underfloor Heating Systems

There are two types on underfloor heating system, wet and dry. The dry system is electric powered, and the wet system is heated water pumped through the pipes.

Water Systems

A network of pipes are filled by warm water which is heated by a boiler or heat pump, and concealed within the floor. Typically the pipes are embedded within a floor screed, but they can be used in timber floor settings too.

The water systems are well suited to larger floor areas, and retain their temperature better than the electric systems. The water system is the best option for installing underfloor heating in a new build or when planning a whole house system.

Water system – pros

• Extremely efficient to run
• Works at low temperatures
• Work well with use alongside heat pumps

Water system – cons

• Initial costs are high
• Pipes are often difficult to reach if there are any problems

Electric Systems

Electric underfloor heating systems consist of cables which are laid over the floor deck.

The electric system is often used in retrofit situations or for smaller spaces like a bathroom. These work really well as they heat up quickly, but they don’t retain their heat in the same way a water system will.

Electric systems – pros

• Inexpensive to install
• No pipework – easy to install

Electric systems – cons

• Expensive to run
• Heavy items and furniture can damage the system

The electric system is more often seen in refurbishment or retrofit as it is a more slimline installation and has less effect on floor levels. It is possible to get low profile water systems for renovation projects however.

Wet systems are more often seen in new build scenarios, due to the increased floor thickness that is required for them. Water systems can also benefit from the varying renewable heat sources available such as air source heat pumps, ground source heat pump, biomass, and so on. The electric system is more limited.

Underfloor Heating Floor Types

Floating

When installing an underfloor heating system within a batten space the system must be in contact with the floor deck in order to provide good thermal performance.

A typical build up for a batten floor underfloor heating system would be:

• Subfloor
• Floor insulation with pipe trenches, between battens
• UFH tubes/pipes
• Chipboard deck
• Flooring finish

This system is a dry floor construction giving a medium heat output and a medium response. It is lightweight and quick to install, and allows for floor coverings to be installed immediately. This is suited to an intermittent heating application.

Suspended

Timber suspended floor using joists to support the deck.

image credit: OMNIE

The underfloor heating system to a suspended floor usually fits between or straddles the joists. This system is suitable for new projects, extensions, and also retrofit options.

A typical build up for a suspended floor:

• Insulation between joists
• Pipe mat with trenches
• UFH pipes/tubes
• Chipboard deck
• Flooring finish

This system is a dry floor construction giving a medium heat output and a medium response. It is lightweight and quick to install, and allows for floor coverings to be installed immediately. This is suited to an intermittent heating application.

Screed

Common underfloor heating construction filling with screed or concrete.

image credit: Nu Heat

Screed is frequently used in floor construction and particularly popular with underfloor heating systems. It is suitable for use in new builds, extensions, over solid slabs or beam and block. It does provide a deeper system and therefore a thicker floor build up than the dry systems mentioned previously.

Typical build up of a screed underfloor heating system where an intermittent heating application is required:

• Concrete slab
• Floor insulation
• Protection layer
• Clip track for pipes
• UFH pipes / tubes
• Sand and cement screed
• Floor covering – usually tiles, ceramic etc

A typical build up of a screed underfloor heating system where 24 hour heating application is required:

• Floor insulation
• Concrete slab
• Protection layer
• Clip track for pipes
• UFH pipes / tubes
• Sand and cement screed
• Floor covering – usually tiles, ceramic etc

Note that on the 24hr heating requirement, the floor insulation is under the concrete slab to allow the thermal mass of the concrete to absorb the heat.

This is a wet floor construction, gives a high heat output and works well with a longer heating cycle. Floor coverings must be fitted after the screed is dry.

There are also retrofit systems, and many acoustic options out there too.

Floor finish options

What is the best floor finish with underfloor heating?

Stone and Ceramic Floor Coverings

Hard flooring like stone or ceramic finishes are the most preferable option for underfloor heating as they provide the most efficiency.  They have a high and even heat transfer, are durable, and can be installed on any floor level.

Stone and ceramic flooring will not be affected by the fluctuating temperatures, so would not be prone to damage.

Polished Screed and Resin

An increasingly popular choice of floor finish in domestic properties, polished screeds and resins are durable and work well with underfloor heating.

They provide an even and efficient heat transfer, with the screed acting as a thermal store thus holding the heat for longer.

Timber Floor Coverings

Solid wood floors are not always considered to be appropriate for underfloor heating as they struggle to cope with the constant fluctuating temperatures and it is likely they will become warped and damaged over time. Care must be taken to select the board width and thickness to ensure compatibility.

Engineered wood is more suitable, as it can perform well with the fluctuating temperatures.

Timber transfers heat well and is available in a wide range of colours, patterns and finishes.

If specifying timber floors with underfloor heating, discuss the options and requirements with your timber floor supplier to ensure the floor is compatible with the system and operating temperatures.

Vinyl and Linoleum Floor Coverings

Vinyl and laminate floor coverings are suitable for underfloor heating, and provide a more affordable option than hard woods or ceramic tiles.

Heat can permeate a vinyl/lino covering well as it is a fairly thin material. Be sure to check with the manufacturer that the vinyl is suitable for use with underfloor heating.

Carpet Floor Coverings

Carpets can be used with underfloor heating, but the Tog value of both the carpet and underlay must not exceed 2.5.

For those who want a traditional design scheme carpets are certainly an option, refer to the carpet manufacturer to ensure the carpet is suitable, and the underlay does not contain polyurethane or felt as these can affect heat transfer.