Wall heating

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Plastic-aluminum pipe plastered with clay
Wall heating: dry construction system multi- concrete prefabricated wall

The wall heating is a family of surface heating and provides a space by releasing heat of the walls with a relatively high proportion of radiation for heating. It is preferably operated in the low temperature range.

The advantage of wall heating lies in the direct heat transfer through the heat radiation of the heated wall surfaces, while the room air is not heated as much as with convector or warm air heating .


The Romans already used the principle of combined floor and wall heating in the hypocaust : cavities in the floor or in the walls were heated by exhaust gases and / or warm air . The first hot water wall heating was installed in England around 1910. The first modern wall heating with plastic pipes was presented in 1971, at the same time as underfloor, wall and ceiling heating.


Outside wall heating / cooling (inside)

The system is laid in plaster or as a dry construction system. Solid masonry must be provided with thermal insulation on the outside or inside so that too much heat is not lost directly through the wall. This arrangement is considered to be physiologically beneficial, as a very even temperature distribution in the room is achieved. If there are large window areas in the outer wall, special measures are required to prevent comfort in the room from suffering from the cold window areas or the development of air turbulence. A particularly good insulating glazing should be chosen and the heat output of the wall heating should be concentrated around the windows and in the reveal. For glass surfaces that reach down to the floor, additional heat-radiating elements in the form of plinth heating or (underfloor) convectors should be provided.

Interior wall heating / cooling

If there is not enough space on the outer walls to install the wall heating, the inner walls can be heated as an alternative. However, this requires a very well-insulated outer wall, since otherwise temperature differences will arise between the walls, which can lead to the formation of an air vortex.

Component heating

While the wall should otherwise be heated as close as possible to the surface in order to enable the cooled-down rooms to heat up quickly, with component heating / cooling, walls or other massive components are heated from the inside and function as thermal energy storage. Since the large storage mass does not allow rapid regulation, this system should only be used in continuously used rooms or to cover a basic load ( temperature control ) in addition to an additional heating system. Component activation is mainly used in large buildings or in basements, as well-insulated small buildings quickly overheat under the influence of solar radiation if the heating system is so sluggish that it cannot react to it.

Furnace heating and hypocausts

The relatively large heated surface of a tiled stove can, depending on the size of the stove, have a similarly positive effect on the room climate as wall heating. The high proportion of radiation from a traditional basic oven leads to the heating of the surrounding walls, which can then radiate the heat again themselves (although not to the same extent as directly heated walls). This is all the more true for hypocaust heating , in which warm air is passed through cavities in the wall in order to warm them up. However, since tiled stoves and hypocausts are often installed inside the building and not on the outer wall, there is again the risk of an air roll forming between the cold outer wall and warmer inner walls.

Tiled stoves with a free-standing heating insert and openings for the air that is heated inside do not have the positive properties of solid masonry tiled stoves, as here, as with convector heating, primarily the room air is heated, while the walls remain rather cold and air turbulence in the room is likely.

Advantages and disadvantages

Disadvantages compared to underfloor heating

  • The outer wall area is usually less than the floor area and is further restricted by window areas. Furniture later placed in front of the outer wall further reduces the area that contributes to heating the room.
    • The smaller area makes higher flow temperatures in the heating circuit necessary. This often leads to a reduced efficiency of condensing boilers and heat pumps .
    • In the case of large window areas in the outer wall, it is necessary to additionally heat the inner wall surfaces. At cold outside temperatures, this can lead to a noticeable circulation of air from the cold outside wall into the interior of the room, which reduces comfort.
  • If the wall heating is installed in solid walls without an insulating intermediate layer, the heating reacts slowly. It takes longer for the rooms to heat up and for a reaction to additional heat input from solar radiation.

Advantages over underfloor heating

  • The heat radiation from the side is more effective, more pleasant and physiologically beneficial than radiation from above or below.
  • It is not necessary to limit the flow temperature of the heating circuit to 29 ° C using special control devices, as specified in DIN for underfloor heating.

Technical design


External walls must have sufficient thermal insulation . With poorly insulated exterior walls, the transmission heat losses are high, so that high energy costs can be expected. A U-value (formerly k-value) of <0.35 W / (m² · K) is a guideline . A U-value of at most 0.45 W / (m² · K) is recommended for old buildings. Under certain conditions, old buildings with half-timbered , natural stone or brick walls can be retrofitted with thermal insulation from the inside. Attaching the wall heating to interior walls is energetically more advantageous, but physiologically unfavorable. Partition walls between different usage units that are provided with wall heating should have an R λ value of at least 0.75 (m² · K) / W.

Energy efficiency

The increased wall temperature on external walls leads to increased energy losses.


  • Outside temperature 0 ° C
  • Inner wall temperature without wall heating 20 ° C
  • Inner wall temperature with wall heating 30 ° C

Since the heat dissipation depends directly on the temperature difference between outside and inside, the heat loss for the alternative with wall heating will regularly be higher. On the other hand, wall heating reduces the moisture content of the wall and thereby improves its thermal insulation value ( U-value ). However, this is not enough to fully compensate for the increased heat loss.

If additional facade insulation is not an option, interior insulation panels made of wood fibers , cork, cellulose , calcium silicate or other materials that are capable of capillary drainage of the condensation water that occurs in winter can be applied to the wall surface before the wall heating is installed .


Wall heating on an outside wall

Wall heating systems are designed in accordance with the heating demand calculation . In general, the following assumptions are made:

  • Room temperature 20 ° C for normal rooms and 22 ° C to 24 ° C for bathrooms.
  • The surface temperature of the walls should not exceed 40 ° C if possible, as otherwise the temperature gradient to the inner walls and window surfaces may be uncomfortably noticeable.
  • The lowest air temperature to be assumed depends on the respective location, e.g. B. Berlin −14 ° C.
  • For hot water heating systems, the flow temperature is preferably 35 ° C when using a heat pump , and 40 ° C to 45 ° C for other heating sources. The return temperature is then usually around 5 ° C lower. If there is only little wall space available for installing the wall heating, higher temperatures are also conceivable. At flow temperatures of over 60 ° C, however, there is no longer any advantage over heating systems that are easier to install, less sluggish and more effective, such as baseboard heating . The air heated convectively by the skirting board system rises at a correspondingly high flow temperature due to the Coanda effect directly along the wall and heats the wall surface in the same way as a system embedded in the wall.

Covering heating surfaces with furniture, curtains or textile wall hangings makes the system sluggish (e.g. carpet on underfloor heating) and also inefficient if it is an outside wall. The necessary storage space for furnishings must therefore be taken into account when arranging the heated wall surfaces.

The position of the heating loops should be traceable and documented (photo with a tape measure) in order to avoid later damage by hammering nails or holes. Detection devices that detect metal, water veins or other materials built into the wall can be used to subsequently determine the course. During the heating season, thermal imaging cameras and temperature-sensitive foils are also suitable for displaying the heat sources.

heating capacity

If multi-layer composite pipes with a diameter of 16 mm are laid at a distance of 10 cm and embedded in a 30 to 35 mm thick layer of plaster, the heating output is around 85 W / m² if the flow temperature is 35 ° C. 1 m² of this system contains approx. 1 liter of water.

To limit the surface temperature of the wall, the heating limit curve can be determined: Heat transfer coefficient 8 W / (m² · K) × max. Wall excess temperature at 40 ° C physical limit temperature With wall heating, the heating limit curve is approx. 160 W / m².

Example of a design heat flow density : heat transfer coefficient 8 W / (m² · K) and an excess wall temperature of approx. 8 K at 35 ° C flow temperature and 20 ° C room temperature with a system embedded in the wall plaster results in a heat flow density of approx. 66 W / m².

Installation of wall heating

The wall is usually heated by pipes or electrical heating elements running close to the wall surface.

Pipes or electrical heating cables are predominantly fastened to the shell wall or the insulation layer and plastered . Instead, prefabricated heating registers, capillary or electric heating mats can be used to speed up installation on larger areas. The thickness of the plaster covering over the top of the pipe is usually 1 cm. When using a suitable factory dry mortar , 5 mm may be sufficient.

Prefabricated, self-supporting heating elements in the form of drywall panels that are screwed to the existing wall or to an independent substructure are also increasingly being offered. Flexible lime , gypsum and clay plasters are particularly suitable as plasters . Plasters with larger proportions of hydraulic binders such as cement or silicate are often too rigid and inflexible and can tear due to thermal expansion or come loose from the wall. A reinforcement fabric made of fiberglass or jute should be worked into the last layer of plaster . When using traditional plaster mortars, the plaster thickness is usually a total of 30 to 35 mm.

Cladding the heated areas with natural stone , tiles or hard cladding is usually possible without any problems. If there is a risk of later moisture penetration of the wall, the use of clay and gypsum plaster should be avoided. Since water- and vapor-tight wall coverings prevent the wall from drying out quickly, these plasters would soften. When laying pipes made of copper or steel, one of the following measures should be taken to prevent rigid wall coverings from being damaged by the stresses that arise when they are heated:

  • The wall temperature is limited to a harmless level by thermal regulating valves , return temperature limiters, a mixer circuit or other safety devices.
  • Before the plaster finally sets, the pipe system is heated once to the highest temperature possible during later operation. The pipes expand and create the space they need when they heat up through local displacement of the plaster. Here it must be taken into account whether the setting process of the plaster used is disturbed by the heating. In addition, the plaster should be kept moist to prevent it from setting prematurely.
  • With every change of direction, the free expansion of the laid pipes is made possible by the addition of a flexible, soft material.
  • The pipes are embedded in a soft-setting mortar, which decouples the subsequent layers from the expansion of the pipes. The mortar in which the wall covering is laid should then be reinforced with a fabric insert or expanded metal.

The information on the maximum flow temperature that the wall heating system can withstand without damage varies greatly. Occasionally 80 ° C is stated. When using clay plaster and temporarily heating the system while the plaster dries, 95 ° C is also possible.

Hot water heating

Wall heating is a further development of underfloor heating , whereby the screed is replaced by a thick layer of plaster. Pipes or capillary tube mats are attached to a wall . According to the pipe arrangement, a distinction is made between register systems in which register pipes are attached between the flow and return pipes - their advantage is e.g. B. their short response time - and endless pipe systems, as usual in underfloor heating technology, which are rather inexpensive. The flow and return should be run as parallel as possible, because then warmer and colder water flow close together and the average temperature of the water is thus evenly distributed over the entire surface of the wall. The water is transported by a circulation pump. The pipe material used is copper or metal composite - 12 to 16 mm in diameter are common - or plastic. Smaller pipe diameters are also possible or common for register systems. Pre-assembled or standardized elements are offered that only need to be attached to the wall and connected to one another. The distance between the pipes is between 5 and 20 cm. Wall heaters are integrated into the interior and exterior walls. This is done as a

  • Wet system
  • on site by plastering (also afterwards)
  • Laying in rails that are attached to the wall
  • Dry system
  • by applying installation plates (wall heating in drywall)
  • of polystyrene rigid foam with heat conducting strips, integral plastic tube and a cover with plasterboard
  • Earth building panels or drywall panels with an integrated pipe system
  • Laying in rails that are attached to the wall, under drywall

The system is laid in the plaster or as a dry construction system and allows any operating temperature, including high operating temperatures in heating mode. In the case of gypsum plastering, it is recommended not to exceed flow temperatures of 50 ° C.

electric heating

For electrical wall heating, a thin heating mat is applied or plastered to the wall, through which electrical current is then passed, which heats the conductor. For this purpose, mats of different sizes and heating capacities are available in stores.



According to the principle of the Roman hypocaust , heated air is passed through cavities in the wall. The enclosed air is heated at the bottom, rises and gives off its heat to the wall, in order to then sink again and be heated again - a kind of cycle (can also be supported by fans ).

Exhaust gases

Behind the wall to be heated there are mostly horizontal trains of a tiled stove . This can be heated outside to keep dust and ash away - or it is also integrated into the room.

Pipe systems

Laying wall loops made of oxygen-tight plastic pipe is unproblematic in every respect. Attention must be paid to the heat resistance of the pipe if parts of the heating system are operated at a higher temperature, since if the mixing valve malfunctions, the wall heating can also be loaded with the higher temperature. In the event that the pipe is stuck with a nail or the like. pipe connectors or repair sleeves in the appropriate sizes should be kept ready. The position of pure plastic pipes cannot be determined with conventional cable locators. When the heating is in operation, the pipes can be located with heat-sensitive foil. The pipe itself is usually not damaged by freezing of the pipes if the heating system fails. Due to the elasticity of the pipe, temperature fluctuations do not lead to significant stresses in the material. The service life of the pipes clearly depends on the quality of the material used.

The plastic pipes are usually laid continuously in a length from a central distribution box, so that no intermediate connectors have to be placed on the wall surface, which would require a greater thickness of plaster or a recess in the wall surface.
If the heating system is to be supported by solar-generated heat, the flow temperatures can be reduced even further by using systems with small pipe spacing or capillary mats, which enables better utilization of the solar heat. If the material is not oxygen-tight (e.g. polypropylene ), the heating circuit must be separated from the boiler circuit and there must be no brass components in the heating circuit. The usual maximum length of the individual heating circuit is 80 m for a 16 mm multilayer pipe.

Laying copper pipes is much more complex, as the pipe cannot be bent without tools and significantly more press or soldered connections are required. Installation can be simplified by using prefabricated pipe registers. According to the laying guidelines , pipe connections are to be brazed with soldered fittings if they are plastered or cast in the screed in order to achieve increased tensile strength. However, when embedding in clay plaster or non-hydraulic lime plaster , the heating loops are regularly soft-soldered, as these plasters are flexible enough to allow the pipes to expand thermally. When using pressure-resistant plasters , the risk of leaky pipe connections and plaster cracks can be significantly reduced if the heating circuit is heated up after plastering, so that the pipes can create space to expand while the plaster is still soft. Clay plaster can be heated dry in this way. Air-lime plasters, on the other hand, have to be kept moist for at least a week, or better for several weeks. If the heating circuit cannot be heated up, plastering should be done at a temperature that roughly corresponds to the mean value between the lowest room temperature and the highest expected flow temperature. For example, if the former is 0 ° C and the latter is 60 ° C, the room should be heated to 30 ° C until the plaster stiffens.

Copper pipes should be laid in walls made of alkaline building materials ( cement and lime plaster ) with a protective coating if it is to be expected that the wall structure will be more frequently soaked through the effects of driving rain, rising soil moisture or splashing water. Normally no moisture penetration is to be expected during heating operation. Small holes in copper pipe can be repaired simply by soldering on a piece of copper sheet, which is e.g. B. was cut from a piece of pipe of the next larger nominal size. Copper pipe is usually not destroyed by freezing the water it contains, but soldered connections can leak and be pushed apart. Smaller leaks can usually be eliminated with a commercially available sealant for heating systems.

When installing the pipe system, care must be taken to ensure that soldered connections are not excessively stressed by changes in the length of the pipe in the event of temperature fluctuations in the heating medium, by limiting the length of the straight pipe sections or by surrounding the pipe with elastic material in a certain area when the direction changes. The thermal load on the pipe connections can also be reduced by installing a small buffer storage tank or a separate boiler circuit, which is decoupled from the heating circuit by means of a hydraulic switch and a second pump.

In contrast to soldered fittings , the sleeves of press fittings have an external bulge, which means that the pipes near the fittings do not lie completely against the wall. Practical experience is still limited, but it is to be expected that pressed connections may be less sensitive to thermal stresses and freezing of the pipe system than soldered connections. It is still unclear whether the O-rings inserted in the press fittings allow the same life expectancy as classic pipe connections , which in the heating circuit can get as old as the building itself.


Wall heaters emit their heat with a relatively high proportion of radiation. This creates a pleasant room climate and low dust turbulence. Energy savings are possible through subjectively perceived warmth at objectively slightly lower room temperatures (in comparison lower flow temperature). With a surface temperature of the wall of 24 to 29 ° C, the radiant heat is perceived as pleasant. In general, the following applies: The smaller the difference between the average room temperature and the surface temperature of an unheated exterior wall, the more comfortable you feel in this room. With the same surface temperature, radiation from the wall is perceived as more pleasant than that of underfloor heating.

Web links

Standards and guidelines

  • DIN EN 12 64: Heating and cooling systems integrated into the room with water flow
  • DIN EN 12 831: Heating systems in buildings - Method for calculating the standard heating load
  • DIN EN 12 828: Heating systems in buildings - Planning of hot water heating systems
  • DIN EN 18 380 VOB Part C: Heating systems and central water heating systems
  • DIN 4103-4: Non-load-bearing internal partition walls; Substructure in wood construction
  • BVF (Federal Association of Surface Heating) guidelines
  • Guideline for the manufacture of heated wall structures in residential, commercial and industrial buildings
  • Guideline for the installation of surface heating in the modernization of existing buildings
  • Earth building rules of the umbrella association Lehm e. V., Weimar

Individual evidence

  1. Hans Schiebold: Heating and water heating in Roman thermal baths historical development - successor systems - modern considerations and investigations . Books on Demand, Norderstedt 2010, ISBN 978-3-8391-1398-1 , pp. 64 u. a . ( limited preview in Google Book Search [accessed December 31, 2016]).
  2. del: New underfloor heating with plastic tubes. Westdeutsche Zeitung May 22, 1971.
  3. Theresia Schräder: No more ice legs with thin plastic tubes. In: Kölner Stadt-Anzeiger, Leverkusen edition , January 7, 1971.
  4. Bernd Sonnenberg: New idea promises: Grandpa's heating is dead. In: Leverkusener Rundschau , January 7, 1971
  5. Thomas Löther: Investigations into the temperature control of historical buildings . disserta Verlag, 2014, ISBN 978-3-95425-484-2 , p. 8 ( limited preview in Google Book Search [accessed December 31, 2016] illustrated).
  6. a b c according to the planning documents for the Hypoplan wall heating system from KME.  ( Page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Accessed May 2016@1@ 2Template: Toter Link / www.schlenker-gmbh.com / media / pdf / hypoplan_technik.pdf  
  7. planning folder . WEM wall heating GmbH, Koblenz
  8. German construction magazine, 2006, chapter: drywall wall heating systems
  9. Cuprotherm plan ( Memento of the original from May 19, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (formerly Hypoplan). Pipe register made of 10 mm copper pipe from KME, accessed in May 2016 @1@ 2Template: Webachiv / IABot / www0.kme.com
  10. Daniela Trauthwein, Kerstin Volkenant, Peter K. Wolff, Melanie Goldmann: Healthy building and living . 1st edition. Haufe, Rudolf, 2008, ISBN 978-3-448-08791-8 , pp. 147 ( limited preview in Google Book Search [accessed December 31, 2016]).