Frequently asked questions about floor heating and cooling

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Common questions about floor heating and cooling – answers from practice

Floor heating and cooling are topics that generate a lot of questions – from the most basic to detailed technical problems that even experienced plumbers face. If you've looked at any forum, you've probably come across dozens of different answers to the same question, each claiming something slightly different. The goal of this article is to consolidate the most frequently asked questions into one clear place with concise, practically verified answers – without unnecessary theorizing, but with a focus on what actually works under the usual conditions of Slovak buildings.

Over the years of practice, we've seen the same questions repeat over and over: What temperature should the water be? Why do I have cold spots on the floor? Can I install floor heating in an older house? Can floor heating also be used for cooling? Each of these questions has its answer – but that answer depends on the context, and this is something many people neglect.

Basic principles: How does floor heating actually work?

Before we get into specific questions, it's good to have a clear understanding of what floor heating actually is and what you can expect from it. The principle is simple: instead of heating a room locally (with radiators, convectors, or infrared panels), you heat the entire surface of the floor, wall, or ceiling. Heat is then radiated evenly into the space from this surface.

The most common type is floor heating – pipe embedded in the floor structure through which warm water flows (usually 30–45 °C in a low-temperature heating system). The floor is heated to 26–29 °C (up to 29 °C in living areas according to the standard, up to 33 °C in bathrooms), and heat spreads by radiation upwards.

Less common, but increasingly popular, is wall and ceiling heating – the same principle, just with a different layout. Ceiling heating is also interesting from the perspective of cooling, as a cool ceiling functions as a natural radiant cooler.

What is the correct water temperature for floor heating?

This is one of the most popular questions, and also the one for which people most often get wrong answers. The correct temperature is not a single number – it depends on several variables.

In most standard living spaces, the supply temperature (outlet from the boiler/heat pump) ranges between 30 and 45 °C, with the return being 5–10 °C lower. It is very important to understand this: floor heating is low-temperature not because it is weak – it is low-temperature because it has a large surface area through which it transfers heat, and that surface does not need to be "charged" to a high temperature.

Specifically: with a pipe spacing of 15 cm and proper floor insulation, a supply temperature of around 35 °C is usually sufficient to cover the heat losses of a standard low-energy house. In older, less insulated buildings, you may need to go up to 40–45 °C. A temperature above 50 °C is unsuitable for floor heating – it risks damaging the pipe, the floor covering, and especially exceeding the hygienically acceptable surface temperature of the floor.

In practice, an equitemperature regulation is set: the boiler or heat pump adjusts the water temperature according to the outside temperature. The warmer it is outside, the cooler the water going into the system. This ensures that in mild weather the system runs at 30 °C and in freezing weather up to 45 °C – and the floor never overheats.

Why do I have cold spots on the floor? Most common causes

Cold spots on the floor are a very common complaint – and there are several reasons for them. From practical experience, these are the most common problems:

Unbalanced circuits – if one circuit consumes significantly more water than another, shorter circuits overheat and longer ones remain cold. Solution: hydraulic balancing at the manifold.
Air in the system – air bubbles block the flow in part of the circuit. Solution: bleeding (see the topic Maintenance and bleeding of the floor heating system for more details).
Improperly laid pipe – a larger spacing in a specific area (e.g., bypassing a column, utility lines). Solution: when planning, consider obstacles and maintain even spacing.
Too thick a surface layer – a thick carpet with padding, wooden floor with thick air gaps reduces performance. Solution: choose an appropriate floor covering.
Incorrect insulation – if the insulation under the pipe is not continuous or is missing, heat goes downward into the lower floor, not upward into the room.

In practice, we have resolved several cases where the customer complained about cold corners in the room – after inspection, it turned out that the pipe was laid in a spiral and the corner areas had a return branch with a low temperature. The solution was simple: re-regulation of the circuit and in one case, the addition of a small electric corner heating element.

How many centimeters from the wall should the pipe be?

The standard STN EN 1264 speaks of an edge zone near external walls, where the pipe spacing is reduced – usually to half the basic spacing. So if the basic spacing is 15 cm, the pipe is laid every 7.5 cm (or 10 cm) near the external wall.

Why? External walls have higher heat losses, so a higher specific output is needed there. This edge zone usually has a width of 0.5–1 m from the wall.

For internal walls and walls leading into heated rooms, this reinforcement is not necessary – heat losses are minimal or zero.

For proper pipe fixation during installation, various tools are used. The pipe fixing strip 16–18 mm allows for quick and accurate placement of the pipe with an adjustable spacing, which is especially valuable when working with a grid foil. To change the direction of the pipe when turning the manifold, the pipe fixing arc PEX 16–18 mm is used, which prevents uncontrolled deformation of the bend and at the same time keeps the pipe in the correct position.

Can I install underfloor heating in an old house or apartment?

Yes, but with limitations and after careful consideration. This is a topic where you need to be honest: a reconstruction with underfloor heating is demanding and not always economically viable.

Main issues in old buildings:

Floor height – the underfloor heating system with insulation board, piping and anhydrite adds at least 6–10 cm (sometimes more). This can be a problem with low ceilings or height differences between rooms.
Heat loss of the building – underfloor heating has a limited specific output (up to 100 W/m²). If the house has high heat losses (an older radiator system calculated with 80 °C water and 150 W/m²), underfloor heating alone may not be sufficient.
Condition of the subfloor – cracks, unevenness, moisture – all of this must be addressed before installation. Moisture is especially critical.
Heat source – an old boiler for 80 °C water must be replaced by a condensing boiler or heat pump, which operates at low temperatures.

In practice, reconstruction with underfloor heating is most often implemented during a complete renovation of the apartment core (bathroom, kitchen) or during a general reconstruction of the entire building. A partial reconstruction of one room is technically possible, but it requires careful connection to the existing system.

System boards vs. grid foil – what is suitable for whom?

This is a question that everyone who designs underfloor heating has to address. Both solutions have their place and are both commonly used.

System board (with nops or channels) is faster to install – the pipe is simply clicked into the nops and holds by itself. The insulation is integrated, which saves time. It is ideal for larger new buildings, where the investment in a more comfortable installation is justified.

Grid foil is a cheaper solution, where the foil serves the function of a separating and positioning layer. The pipe is fixed using clips or strips. With this method, a separating layer must be placed under the foil. For this purpose, for example, the separating grid foil 0.1×1030 mm with an aluminum layer can be used, which serves the function of a reflective barrier and at the same time separates the insulation from the screed layer. The joints of the foils are sealed with a special metallic tape 55 mm × 50 m, which ensures that the foils do not shift and the joints are airtight.

More about this comparison can be found in the topic System board vs. grid foil – what is better for your subfloor? in the Knowledge Center.

Can I also cool with underfloor heating? What should you know?

Yes, in principle it is possible – but with major reservations and conditions. Cooling via floor piping works by cold water (usually 16–20 °C) flowing through the system and the floor absorbing heat from the room by radiation downwards.

Basic limitation: dew point. If the floor surface is cold and the air humidity is high, moisture can condense on the floor – this is not only unpleasant, but also dangerous (risk of slipping, damage to the floor covering, mold). Therefore, the cooling system via the floor must be equipped with a dew point sensor, which automatically stops the cooling when there is a risk of condensation.

The efficiency of floor cooling is limited – it does not reach the performance of a conventional air conditioning system. In practice, floor cooling can reduce the room temperature by 3–5 °C compared to the outside, which in the climatic conditions of Slovakia in summer (30–35 °C) is not always sufficient for comfortable cooling.

Ceiling cooling is much more effective: a cold ceiling carries a greater risk of condensation towards the room (condensation would drip), but the air cools and sinks down without the risk of condensation on the ceiling surface (if the surface is a bit warmer than the air's dew point). In practice, ceiling cooling is combined with controlled ventilation (MVHR), which controls the humidity.

More details about the requirements for floor composition in combined heating and cooling can be found in the topic Underfloor heating and cooling – what must the floor composition meet?

What is the specific performance of floor heating and is it enough?

This is a question that people who are afraid that floor heating will be "weak" often ask. In reality, if the system is properly designed, floor heating fully covers heat losses even in well-insulated homes.

The specific performance of floor heating depends on the water temperature, pipe spacing, and thermal resistance of the floor covering. In practice:

With 10 cm spacing and 45 °C supply: up to 100–120 W/m²
With 15 cm spacing and 40 °C supply: approx. 70–90 W/m²
With 20 cm spacing and 35 °C supply: approx. 50–70 W/m²

A low-energy house typically has heat losses of 20–40 W/m² (floor area). This means that floor heating with 20 cm spacing and low water temperature fully meets the needs. A passive house has even lower losses.

Problems arise in older houses with heat losses of 60–100+ W/m². In such cases, it is appropriate to either combine floor heating with radiators (in critical areas) or to first insulate the house and then address the heating.

More on the calculation of spacing and pipe diameter can be found in the topic What pipe diameter and spacing do I need for floor heating?

How long does it take for the floor to heat up or cool down?

Thermal inertia is one of the key differences compared to radiator heating. Floor heating has a high thermal capacity – how much heat the floor construction can absorb and gradually release. This property is both an advantage and a disadvantage.

Advantages of thermal inertia: The system behaves like a heat accumulator. Even if the boiler is briefly out (power outage, service), the floor remains warm for several hours. Temperature fluctuations are small and slow – the room has a constant comfort without "thermal shocks".

Disadvantages of thermal inertia: If you want to quickly change the temperature (you wake up in the morning and want it warmer), the system does not react immediately. Heating up the floor takes 2–4 hours from a cold state with a standard anhydrite screed. Therefore, floor heating is unsuitable for buildings with irregular, short-term occupancy (e.g., a cottage where you come once a week for the weekend).

In practice, most systems are controlled by an equitemperature control that works smoothly and not abruptly – the floor never reaches a "cold starting" temperature, only slightly fluctuates around the set value. This largely eliminates the problem of thermal inertia.

Floor heating and wooden floor – is it possible?

Yes, but with conditions. Wood is a thermally more problematic material than ceramic tiles – it has a higher thermal resistance, which reduces the system's efficiency. In addition, wood is sensitive to temperature and humidity.

The following rules apply to floor heating with wooden floors:

Maximum floor surface temperature: 27 °C (some wood manufacturers specify 26 °C). At higher temperatures, wood cracks, dries out, and deforms.
Thermal resistance of the floor covering (Rλ,B) should be max. 0.10–0.15 m²K/W for wooden floors intended for floor heating. The manufacturer must state that the floor is certified for floor heating.
Wood moisture content must be stabilized. The wood must be acclimatized before installation, and room humidity must be kept stable (40–60 % RH).
Solid wood vs. engineered parquet – engineered wooden floors are more dimensionally stable and more suitable for floor heating than solid wood.

Carpets are problematic in terms of efficiency – a thick carpet with a thick underlay has a high thermal resistance and significantly reduces the system's performance. A thin carpet (Rλ,B up to 0.10 m²K/W) is still acceptable.

Separation film and subfloor preparation – what to pay attention to?

Subfloor preparation is one of those things where savings are often made in floor heating where they cannot be made. Incorrect subfloor preparation causes problems that are difficult to solve without breaking the floor.

The subfloor must be:

Flat – deviation max. 5 mm per 2 m straightedge. Unevenness causes insulation boards to "bunch up" and lose contact with the subfloor.
Dry – the moisture content of the subfloor (concrete) should not exceed 4–5 % for conventional concrete, 0.5 % for anhydrite. In case of suspected moisture, it should be measured and, if necessary, a waterproofing film should be laid. More in the topic Waterproofing film under floor heating – when and how to use it?
Stable – a loose, crumbling subfloor should be stabilized with penetration or replacement.

A separation film is laid on the insulation before pouring anhydrite or concrete. Its function is to prevent the poured mixture from penetrating into the insulation and at the same time allow minor movements between the layers. The films are joined with an overlap of at least 15–20 cm and glued with metallic tape. Metallic tape 55 mm × 50 m is ideal for this purpose – it holds even during thermal expansion and does not melt during anhydrite pouring.

A perimeter expansion strip (skirting strip) is laid around the room before pouring – it ensures that the screed can freely expand and contract without causing cracks.

Fixing the pipes – what are the options and what is the fastest?

Proper pipe fixing is the basis of a functional system. Pipes that move during pouring or filling the system can cause uneven spacing and cold spots. At the same time, the pipes must be handled carefully to avoid damage.

The fastest method for professional installers is the nailing strip system board – the pipe is simply clicked between the nailing strips and held without further fixation. For systems with foil, there are two standard options available:

Direct pipe clamps – direct pipe clamp 50 mm is driven directly through the foil into the insulation, holding the pipe from the side. Suitable for straight sections, installation is quick.
Mounting strips – mounting strip 16–18 mm / 1 m is laid in strips parallel to the pipe and the pipe is inserted into it. The advantage is an adjustable spacing and secure fixation on long straight sections.

For bends and turns, the pipe fixing arc PEX 16–18 mm is used, which prevents uncontrolled "popping out" of the bend during pressure testing.

More on this topic can be found in the Knowledge Center in the article Fixing the pipe in underfloor heating – clamps, strips and arcs.

What is the difference between anhydrite and concrete screed?

After laying the pipe, the next step is pouring the screed. In practice, two basic mixtures are used:

Anhydrite screed (flow screed): The advantage is that it is fluid and spreads on its own – it does not require vibrators or intensive compaction. It better flows around the pipe and forms a homogeneous layer. It has slightly better thermal conductivity than concrete (approximately 1.6–2.0 W/mK vs. 1.0–1.5 W/mK for concrete). Disadvantage: it is sensitive to moisture and must be sufficiently dry before laying the floor covering (typically 4–6 weeks at 20 °C). It cannot be used in wet areas (bathroom) without a waterproofing layer.

Concrete screed: More resistant to moisture, suitable for use in bathrooms as well. It requires thorough compaction to eliminate the risk of voids around the pipe. Drying is slower (at a thickness of 65 mm, approximately 6–8 weeks). Thermal conductivity is lower, but in a properly designed system, this does not play a crucial role.

The minimum thickness of the screed covering the pipe is usually 45–65 mm for a pipe of Ø 16 mm (depending on the type of screed and floor load). Insufficient thickness of the screed can lead to cracking, pipe impressions on the floor, and uneven heat distribution.

Dilation – why is it important and where is it done?

The screed expands and contracts when heated and cooled. If it cannot move freely, it cracks. Dilation joints are therefore an essential part of every underfloor heating system.

Basic dilation rules:

Edge dilation strip along the entire perimeter of the room (and around columns, penetrations) – at least 8 mm thick strip of PE foam.
Dilation joint in the area is made for large areas (over 40 m², or longer side over 8 m) or for unsuitable shapes (L-shape, irregular floor plans).
Transition of loops across the dilation joint must be protected – the pipe is run in a protective sleeve (a plastic pipe of a larger diameter) at least 0.5 m on each side of the joint.

In practice, we often encounter the situation where customers skip the edge strips due to "savings" and after a year they have to deal with cracks in the screed – and possibly also in the floor covering. The edge dilation strip costs a fraction of the total system cost and is not a place to save money.

Pressure tests – how and when are they done?

Before pouring the screed, a pressure test of the entire pipe is mandatory. This is a check of the system's tightness before covering the pipe with a layer of screed, from which any leak would be difficult to remove.

Pressure test procedure:

The system is filled with water and vented.
Pressure is increased to 1.5× operating pressure (usually 4–6 bar), at least 6 bar.
Pressure is monitored for at least 2 hours (for larger systems even longer).
Pressure drop must not exceed the allowed values (according to the standard STN EN 1264 max. 0.1 bar per hour).

After a successful pressure test, the system is left filled during the entire pouring process to keep the pipe in the correct position and prevent it from sinking into the insulation.

A more detailed description of the entire installation process can be found in the topic Installation of underfloor heating step by step – from insulation to pouring.

How to properly heat up a new floor after pouring?

This is a step that is often skipped or done incorrectly. A new screed must go through a controlled heating process (heating-in period), otherwise cracking and damage to the structure of the screed may occur.

Standard heating-in procedure for anhydrite:

At least 7 days after pouring, the system is not activated at all.
Then the supply temperature is set to 25 °C and left for 3 days.
Every 1–2 days the temperature is increased by 5 °C, until the maximum operating temperature is reached.
The system is left at the maximum temperature for at least 3–4 days.
Then the temperature is gradually reduced back to the operating value.

The whole process typically takes 2–3 weeks. Before laying the floor covering, the screed must be sufficiently dry – this is checked with a measuring device (CM method) or a carbide test. Premature laying of ceramic tiles or wooden flooring on a wet screed is one of the most common mistakes. More on this topic in the article Common mistakes in laying underfloor heating pipes and how to avoid them.

What is a manifold and how does it work?

A manifold (distribution unit) is a central distribution node from which water flows into individual underfloor heating circuits and returns. Each circuit (room or part of a room) has its own supply and return with a regulating valve on the manifold.

Basic equipment of a manifold:

Flow meters – visually indicate how much water flows through each circuit, allowing hydraulic balancing.
Thermostatic valves – allow regulation of each circuit by a thermostat in the room.
Drain-off valves – at the top of the manifold for system venting.
Drain valves – for filling and draining the system.
Actuators – electric actuators of valves, controlled by a thermostat in the room.

The manifold is usually mounted in a special wall cabinet or a large surface cabinet. The height of its installation must allow for venting (air rises upwards, so the vent must be at the highest point of the circuit).

Can I have underfloor heating on a staircase?

Technically yes, but it is more complicated. A staircase is specific in that individual steps are relatively small areas and dilation movements can be larger. In addition, the pipe must be routed in such a way that it does not interfere with the load-bearing structure of the steps.

In practice, electric heating mats are more commonly used on staircases – they are thin, easy to install, and each step can be regulated separately. For external staircases or access ramps (anti-icing), electric systems are also preferred, or special hydraulic anti-icing systems with non-freezing mixtures.

Most frequently asked questions (FAQ)

How much does underfloor heating cost per m² – real numbers?

The price varies greatly depending on the chosen system, insulation thickness, pipe diameter, and region. Roughly: the material alone (insulation, pipe, accessories) for a new family house costs 15–30 €/m² without a manifold and heat source. The installer's work adds another 10–20 €/m². A manifold for 6–8 circuits costs 200–500 € depending on the equipment. Overall, for a standard family house (150 m²), expect 4,000–9,000 € for the entire underfloor heating system including installation, without the heat source.

Do I need a thermostat in each room separately?

It is not mandatory, but it is recommended. Each circuit on the manifold can be controlled manually (you set the flow once and leave it) or thermostatically (a thermostat in the room controls the actuator of the valve). Thermostatic control of each room separately reduces energy consumption by 10–20 % and increases comfort. Without thermostats, you have a uniform temperature throughout the house – which may not always be desirable (bedroom vs. living room).

What if my floor pipe bursts?

Modern PEX or PEX-AL-PEX piping, when installed correctly (without sharp bends, mechanical damage, or joints in the slab), has practically unlimited lifespan. Manufacturers guarantee 50 years. Joints and fittings in the poured slab are prohibited – that is why the piping is run in full lengths from manifold to manifold without interruption. If a failure does occur (damage during renovation, rare manufacturing defect), it is localized using a thermal camera or acoustic detector and resolved by spot excavation.

Can floor heating be powered by solar panels?

Direct heating of floor heating from solar collectors (thermal, not photovoltaic) is possible, but it requires careful design and a thermal storage tank. In the summer, the output of solar collectors is highest, but heating is not needed – the energy is used for hot water heating. In winter, the output of the collectors is lowest, when heating would need the most. Therefore, solar collectors are primarily designed for hot water preparation and only as a supplementary source for heating. Photovoltaic panels combined with a heat pump are today a more economically advantageous and flexible solution.

Is floor heating suitable for allergy sufferers?

Yes – radiation is more hygienic than convective heating (radiators, warm air heating). With radiation, air movement is minimal, and dust and mite dispersion is significantly lower. A floor temperature of around 26–28 °C is also unsuitable for mite reproduction, as they prefer warmer and more humid environments. For allergy sufferers, floor heating is one of the most recommended heating solutions.

Why does the heating "bubble" or make noises?

Noises in the floor heating system are almost always caused by air in the piping. Air accumulates in the highest places in the system – that is, at the manifold and in places where the piping rises upward. Solution: bleeding via air vents on the manifold. The bleeding procedure is simple, but it must be done correctly – more in the topic Maintenance and Bleeding of the Floor Heating System. If air appears repeatedly, it may indicate a leak in the expansion tank or insufficient pressure in the system.

Conclusion: Floor heating as a long-term investment

Surface heating – and especially floor heating

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Having trouble deciding or dealing with a specific situation in your household? Write to us – we are happy to help.