Underfloor heating: costs, installation, and comparison of wet and electric systems

In brief

Wet underfloor heating makes sense in new builds and in renovations where the whole floor is being replaced, especially combined with a heat pump or a condensing boiler. Electric underfloor heating is simpler to install and suits bathrooms and smaller areas as supplementary heating. Whether the system works without problems depends mainly on the circuit design, the pressure test before screeding and correct heating up of the screed before the floor finish goes down. Current installation prices are in the heating work category, and prices for the final floor in the flooring work category.

• Wet system: pipes in the screed, manifold, controls, connection to the heat source
• Electric system: heating mat or cable under the tiles, thermostat with a floor sensor
• Heating up the screed: cement screed no earlier than 21 days, anhydrite screed after 7 days, unless the manufacturer specifies otherwise
• Floor finish: the lower its thermal resistance, the better, with tiles being ideal

Wet or electric underfloor heating: which system should you choose?

Choosing between wet and electric underfloor heating is the most important decision in the whole project. Each system has its own strengths, typical uses and limits, which affect both running costs and comfort for years to come.

Wet underfloor heating: for whole houses and large areas

Wet underfloor heating works by circulating warm water through plastic or multilayer pipes embedded in the screed. The water is heated by a condensing boiler, a heat pump or another heat source and distributed through the underfloor heating manifold to the circuits in each room.

A wet system suits new family houses and full renovations. It runs at a lower water temperature than radiators, which suits heat pumps and condensing boilers well. Heat is released slowly and evenly across a large surface, although the system reacts more slowly when the settings change. The main jobs are fitting the manifold, laying the pipes, screeding over the underfloor heating pipes and setting up the controls. Current prices are in the heating work category.

Electric underfloor heating: for bathrooms and supplementary heating

An electric system uses a heating mat or cable laid directly under the tiles, in the tile adhesive or a thin levelling compound. Installation is simpler, with no manifold or pump, and the floor warms up quickly. The mat is powered through a thermostat with a floor temperature sensor, and the connection to the electrical installation must be made by a qualified electrician. In bathrooms, zone rules also apply, as explained in the article on bathroom electrical installations.

Electric heating is best suited to bathrooms, toilets and kitchens as a supplement to the main heating, or to small spaces where a wet system would not make sense. The limit is running costs: heating a larger area directly with electricity all winter quickly becomes expensive, particularly in countries with high electricity prices.

What makes up the cost of underfloor heating?

The final price depends on the type of system, the floor area, the number of rooms and control zones, and whether it is a new build or a renovation that involves removing the old floor.

• Manifold with valves and the number of circuits defined in the design.
• Pipes and system panels with insulation, perimeter edge strips and impact sound insulation.
• Screed: cement or anhydrite, its thickness and area.
• Controls: room thermostats, actuators and possibly pre-wiring for a smart thermostat.
• Connection to the heat source, pump group, expansion vessel and filling the system.
• In renovations, also removing the old floor and adjusting floor heights and doors.
• The floor finish, which must be suitable for underfloor heating.

As a guide, according to the NUMIQ price list, labour for a wet system, meaning laying the system panels and pipes, costs roughly 9 to 12 € per m², and for an electric heating mat roughly 15 to 18 € per m², in both cases including ancillary materials but excluding pipes, mat, manifold, controls and screed. Current prices for individual heating jobs are in the heating work category, and prices for laying tiles, vinyl or laminate in the flooring work category. Outside the heating season it is usually easier to book a heating engineer.

Many European countries currently subsidise heat pumps, and some also support the low-temperature emitters that go with them, including underfloor heating. Schemes, amounts and application rules differ widely and change often, so check the programme in your country before signing a contract, as many require the application to be made before work starts.

How wet underfloor heating is installed

1. Design. Heat loss calculation for each room, division into circuits, pipe spacing and manifold position. Without a design, some rooms may stay cooler or the circuits may be impossible to balance.

2. Preparing the base. A level base, thermal and impact sound insulation and a perimeter edge strip around each room, which lets the screed expand as it heats up.

3. Laying the pipes and pressure testing. The pipes are laid according to the design and connected to the manifold. A leak test follows before screeding. The protocol of the manufacturer Purmo specifies a test pressure of at least 4 and at most 6 bar for a cold water test, and the screed should be poured while the system is still under pressure. If a pipe is damaged during screeding, the pressure gauge shows it immediately.

4. Screed. Cement or anhydrite screed is poured to the thickness specified by the manufacturer. Anhydrite is self-levelling and widely used with underfloor heating, but once it has hardened the thin surface layer of laitance must be sanded off, otherwise adhesive and flooring will not bond well. Anhydrite is not suitable for permanently damp rooms such as saunas.

5. Functional heating. According to Purmo's protocol, cement screed is first heated no earlier than 21 days after pouring and anhydrite screed after 7 days, unless the screed manufacturer specifies otherwise. For the first 3 days the flow temperature is held at 25 °C, then raised to the maximum design temperature and held for 4 days. The process is recorded in a heat-up log.

6. Drying and moisture testing. Functional heating does not mean the screed is ready for flooring. The flooring manufacturer HARO specifies residual moisture of 1.8 % CM for cement screed and 0.3 % CM for anhydrite screed over underfloor heating, measured with the calcium carbide method. The floor fitter takes the measurement at pre-marked points where there are no pipes.

7. Laying the floor. HARO states that the screed surface should be at least 18 °C and the relative air humidity no higher than 65 % during laying, and these conditions should be maintained for several days afterwards.

When is underfloor heating worth the investment?

When underfloor heating is a good choice

Wet underfloor heating makes most sense in new builds, combined with a heat pump or condensing boiler. The low operating water temperature suits low-energy houses with small heat losses. In renovations it is worthwhile when the floor is being replaced throughout the house and the floor build-up height can be adjusted. Electric underfloor heating is popular in bathrooms, where warm tiles underfoot are particularly pleasant.

When radiators are the better option

In older flats with limited floor height, wet underfloor heating is often technically demanding: the new floor build-up may require changes to door frames and doors, and in apartment buildings any work on the shared heating system usually needs the consent of the building management or owners. In a poorly insulated house, a low-temperature system may not cover the heat loss, and radiators with a higher water temperature will give better comfort. The decision should be based on a heat loss calculation, not a guess.

Which floor finish to choose for underfloor heating

Ceramic tiles and stone work best because they conduct heat well. With wood, laminate and vinyl, the thermal resistance of the whole build-up, including the underlay, is what matters. HARO states that it should not exceed approximately 0.15 m²K/W and recommends that the surface temperature of wooden floors should not exceed 25 °C in operation. The manufacturer must explicitly state that the product is suitable for underfloor heating. Prices for laying the different floor types are in the flooring work category.

What goes wrong in practice: the most common mistakes

Laying the floor on damp screed. The most common and most expensive problem. The laying date is set by the calendar rather than by a moisture measurement. Wooden floors then cup, vinyl comes unstuck and tiles can crack. The solution is to insist on a CM moisture test with a written record.

Skipped functional heating or too fast a start. If the screed is heated to a high temperature straight after pouring, it can crack. If the heat-up is skipped entirely, the screed dries slowly and hidden stresses only show up under the finished floor.

Missing edge strips and movement joints. Screed expands as it heats. Without an edge strip it pushes against the walls and cracks. Larger or irregular areas need movement joints according to the design, with pipes passing through them in protective sleeves.

An unbalanced system. Without hydraulic balancing of the circuits, rooms further from the manifold stay cooler and the system runs inefficiently. Flow rates at the manifold should be set according to the design and recorded.

Choosing the floor too late. A soft carpet with a thick underlay or a thick solid wood floor noticeably reduces heat output. The floor type needs to be known at the design stage.

What clients and contractors most often disagree about

• Who is responsible for screed moisture. The heating engineer, the screed contractor and the floor fitter tend to pass responsibility to each other. A heat-up log and a record of the moisture test before laying help.
• Cracks in the screed. Without records of the joints and the heat-up, the cause is hard to establish.
• Cold rooms. The cause is often a missing design or unbalanced circuits, not a fault in the heat source.

Handover checklist

• Do you have the circuit design and a drawing or photos of the pipe layout before screeding?
• Do you have the pressure test record and information on the pressure the system was under during screeding?
• Do you have the functional heating log with dates and temperatures?
• Is the residual moisture measurement of the screed recorded before the floor was laid?
• Are the circuits on the manifold labelled by room and the flow rates set?
• Do the thermostats work in every room, and is floor overheating protection set?
• For electric heating: was the mat resistance measured before and after tiling, and do you have the electrician's test certificate for the circuit?

How to decide on underfloor heating

With the right design, underfloor heating is a very comfortable way to heat new builds and quality renovations. Before hiring a contractor, ask for a circuit layout design including a heat loss calculation, check that the installer uses system components from a single manufacturer and follows its instructions and the applicable technical standards, and agree a written warranty covering both materials and labour.

FAQ - Frequently asked questions about underfloor heating

How much does underfloor heating cost?

It depends on the type of system, the area, the number of circuits, the controls and whether it is a new build or a renovation. Current prices for individual jobs, calculated from the live price list, are in the heating work category.

Wet or electric underfloor heating: which is better?

For whole houses and larger areas, a wet system is the better choice because of lower running costs with a suitable heat source. For bathrooms and small areas, electric is more practical thanks to simple installation and fast warm-up.

How many circuits and manifolds do I need?

The number of circuits and manifolds is determined by the design, based on heat loss and layout. Larger houses often have several manifolds by floor or zone. Installation prices are in the heating work category.

Which floor finish works with underfloor heating?

Ceramic tiles or stone work best. For laminate, vinyl and wooden floors, the manufacturer must explicitly state suitability for underfloor heating, and the thermal resistance of the build-up should be low, with HARO giving a limit of roughly 0.15 m²K/W.

How long does underfloor heating installation take?

Installing the pipes and manifold in a family house takes a few working days. The screed takes longer: cement screed is first heated after 21 days at the earliest, anhydrite after 7 days, and the floor is laid only once it has dried to the required moisture level.

How long does underfloor heating last?

With quality pipes and correct operation, wet underfloor heating is designed to last for decades. Controls, valves and pumps are replaced more often than the pipes, so the manifold should remain accessible.

Can underfloor heating replace radiators in an older flat?

In older apartment blocks, wet underfloor heating is technically demanding because of floor height and the connection to the building's heating system. Electric underfloor heating in the bathroom, as a supplement to the radiators, often makes more sense.

Work out the cost of underfloor heating for your project

The actual price depends on the type of system, area, controls, region and contractor. Current prices are in the heating work and flooring work categories.

For an initial budget, use the NUMIQ online calculator: choose the type of heating work, enter the quantity and get an indicative price including materials.