Specialist terminology explained


Kermi ABC – specialist terminology explained
acoustic power level

The acoustic power level quantifies all the energy emitted by an object as noise. This value is dependent on location, space, and distance. It can be used for comparisons with other ventilation units, whereas the sound pressure level cannot

Active cooling function

A building can be cooled with the active cooling function. The heat pump needs to be reversible for the active cooling, which means the cooling circuit runs in reverse. Here, the heat is emitted into the outside air from the building using the heat pump. During this process, the compressor of the heat pump runs (is active).

Additional electric operation

Designer radiators with additional electric operation are connected to the central heating network but can be operated independently of it from an electrical perspective. This is particularly suitable in transitional periods and for short-term heat demand. More information on electric operation of designer and bathroom radiators.

Air vent plug

The air vent plug seals the heating system in relation to the outside world. It can easily be removed to bleed the radiator.

All-electric operation

Radiators with all-electric operation are independent of the central heating network; in this case, a socket is the only energy connection required for the installation. Especially in old buildings, they are a time and cost-saving solution for modernisation projects. But even in energy-autonomous new builds with solar panel systems, an electric radiator can provide a way of utilising the self-produced electricity. More information on our electric radiators.

Approval period

If the funding for replacing the heating system is approved by BAFA, it triggers the start of the approval period. During these 12 months, the funded measures are implemented. If the measures are delayed, there is the possibility of extending the deadline.


Firstly, the German Federal Office of Economics and Export Control (BAFA) plays an administrative role in the areas of foreign trade, energy business promotion, and auditor supervision. Secondly, it also promotes energy-efficient technologies and energy-saving measures.

Blanking plugs

A blanking plug seals the heating system in relation to the outside world and hides the opening behind it. It can easily be removed for maintenance work. Blanking plugs are included in the delivery of our radiators.

Buffer charging pump

The buffer charging pump moves the heat generated by the heat pump to the buffer or domestic water tank.

Central ventilation system

A distinction is made between the following:

  • A centrally arranged central system where one ventilation unit is responsible for supplying several housing units.
  • A decentrally (semi-centrally) arranged central system where one ventilation unit is responsible for supplying a housing unit with air and the air is then delivered to the respective rooms by means of ducts.
Cleaning and cleaning products

Dust formation inside radiators is a natural process that is linked to the circulation of the warmed air and cannot be prevented by technical means. Accessible locations should be cleaned periodically with special brushes to ensure optimal heat output. Radiators can be easily cleaned with our special brushes.
You can buy these products from your qualified specialist installer, from specialist wholesalers, or can order them online from our Kermi spare parts shop from the convenience of your own home. To find a specialist partner near you, please refer to our Specialist partner overview.

You can also clean your radiator with household cleaning agents. Cleaning agents used on paint surfaces should not be abrasive. Nor should they be strongly alkaline or acidic (chemically aggressive).
To be able to clean the radiator properly, you first have to remove the top cover. To do this, you need to lift the plastic clip (Kermi clip, can also be ordered from online shop) on the side panel and unscrew anticlockwise. With Plan radiator lengths of 1000 or more or with a radiator length of 1400, the Profil radiator retaining bar also needs to be removed from the top cover. After that, pull the side cover off the radiator at a slight angle, lift the top cover, and detach the side cover from the fixing hooks. Then separate the top cover from the second side cover by lifting it at one side and sliding it. After cleaning, reinstall the top cover by following the steps in reverse order!

Climate Protection Package 2030

Within the framework of the Climate Protection Act, the federal government in Germany has adopted measures that aim to achieve greenhouse gas neutrality by 2050. The programme includes a package of CO2 saving measures for the energy sector, industry, buildings, transport, agriculture and forestry, land use, and waste management. By 2030, Germany intends to reduce its CO2 emissions by at least 55 percent.

CO2 emissions

CO2 emissions means the greenhouse gases produced by the combustion of substances such as coal, diesel, petrol, natural or liquid gas, and wood. The CO2 generated during the combustion process accumulates in the atmosphere and is largely responsible for the greenhouse effect and global warming.

Connection options

Kermi offers a standardised 50 mm centre connection that provides you with complete planning and decision-making freedom from start to finish. The connection remains completely hidden underneath a cover rosette in the case of virtually all valve versions. The classic variant with the side connection on the left and right is also available for many models. With the centre connection, the connection of the feed and return pipe is not important, as there is a stopper (partition) between the two connections. You will find further information on the Kermi connection types in the technical documentation for the respective product.


The coefficient of performance (COP) refers to a defined operating point (e.g. A2/W35 – air temperature 2 °C, flow temperature 35 °C) of the heat pump. The COP is a ratio that expresses the relationship between the output heat and the consumed electrical power at a particular moment in time.

Corrosion protection

In many buildings, radiators are exposed to special conditions which can attack the coating. The Kermi anti-corrosion coating is a special layer which is applied directly to the radiator and is then finished with a high-quality powder coating. It protects the radiator from damage caused by moisture and can also be applied under coloured paint finishes.

Covers and cover rosettes

Radiator covers serve two purposes. Firstly, they protect the inside of the radiator from dirt and, secondly, they are responsible for directing the air flow from the radiator. If the cover is missing, warm air can escape in undesired directions and optimum distribution in the room is no longer ensured.
Cover rosettes are used to conceal unwanted connections or fixings and thus also protect against dirt.

You will find top and side covers for radiators as well as cover rosettes for radiator connections and fixings in our Kermi spare parts shop.


Are you looking for a nearby specialist partner so you can see our products in the flesh, get some advice, or place an order? To find a specialist partner near you, please refer to our Specialist partner overview.

Decentralised ventilation system

As a general rule, decentralised ventilation units with heat recovery only work in individual rooms and are usually operated without a duct system. However, in some cases, a second room is connected to the unit via a pipe system.

EC motor

An EC motor (electronically commutated motor) is a brushless DC motor which takes the form of a three-phase synchronous motor and is excited by permanent magnets. The rotary field is achieved through integrated commutation electronics (reversal of current). A magnetic rotary field is generated in the stator coil by the three-phase supply, which induces a magnetic field in the rotor that then leads to rotation. The advantages are the extremely high efficiency and the infinitely adjustable speed control via the commutation electronics.


The efficiency describes the ratio of useful energy to supplied energy. The higher the efficiency, the more efficiently the unit is working.

Energy Saving Ordinance (EnEV)

On the basis of the Energy Saving Act, the Energy Saving Ordinance (EnEV) sets standard requirements for privately and commercially used new builds, such as apartment buildings, office blocks, etc. This is to ensure that construction projects are built in an energy-efficient way. It is part of German commercial administrative law.


Global leaders in the building industry have joined forces to form the EnOcean alliance. This focuses on energy harvesting wireless switches, sensors, and receivers for building automation with a view to making buildings more energy-efficient, flexible, and cost-effective.

Enthalpy heat exchanger

In contrast to normal heat exchangers, enthalpy heat exchangers can also recover moisture. In the winter, this has the advantage of slowing down the natural drying-out process that occurs in living spaces. This can help to increase the moisture within the living space to a more comfortable level. Particularly at cold times of the year, it is – of course – important to adjust the air flow in line with the actual demand, to reduce the air flow and to prevent the rooms from overheating (temperatures of 23 °C and above) with a view to keeping the humidity at >35 %.

Exchange bonus

From 2026 onwards, no pure oil heating systems are allowed to be installed in new builds. From that point, it will only be permissible to install regenerative systems or to use hybrid systems that rely on renewable energies in addition to oil to generate heat. The German government’s new climate package has comprehensively updated and expanded the market incentive programme. This subsidy is also known as the exchange bonus.

Extract air

The extract air is the name given to the used and contaminated air (odours, humidity, CO2 or other volatile organic gases) which are to be removed from the living space.


Filters can be divided into outside air filters and extract air filters.
The outside air filter ensures that the supply air coming into the house is clean and fresh. It prevents fine dust and pollen – as well as spores, viruses, and bacteria – from getting into the building from outside. In addition to that, outside air filters protect installed components against soiling.
The used air is returned to the outside via the extract air filter. Dust and dirt particles are also filtered out of the extract air to prevent soiling of the unit. This ensures clean operation of the heat exchanger and the efficiency of heat recovery is maintained.

You can order original Kermi filters for your controlled residential ventilation system easily and conveniently from the Kermi spare parts shop. 

Flow temperature

The flow temperature refers to the temperature to which the heating water has to be heated before it flows through the heating system by travelling through radiators and underfloor heating.

Geothermal collector

With brine/water heat pumps, the thermal energy is collected from the environment using a ground collector or ground probes and is converted into thermal heat. Geothermal collectors are generally laid horizontally at a depth of up to 2 m.

Geothermal probe

A geothermal probe collects thermal energy from the environment via one or more geothermal wells with a depth of up to 100 m. For that reason, they require a permit. The advantages compared to geothermal collectors are the significantly lower space requirements and higher source temperature over the year, which allows greater efficiency of the heat pump.

Geothermal probe

A geothermal probe collects thermal energy from the environment via one or more geothermal wells with a depth of up to 100 m. For that reason, they require a permit. The advantages compared to geothermal collectors are the significantly lower space requirements and higher source temperature over the year, which allows greater efficiency of the heat pump.

Heat cost allocator

Most Kermi designer radiators are suitable for heating cost recording using a heating costs allocator. Evaporation counters can also be installed on steel panel radiators. As the positioning of the recording devices differs from one manufacturer to another, please contact the relevant manufacturer for details. You will find further information in our technical documentation for the respective product.

Heat distribution

What should you do if only half of the radiator or only the top gets warm?

If only half of the radiator gets warm but the desired room temperature is reached, then there is no reason to worry. The thermostat controls the flow of water in such a way that this may happen to the radiator in case of partial quantities of water. However, if the radiator remains cold in the lower area and the room temperature drops or no longer rises, you should take action. There are many possible causes for a heating system not heating evenly and they range from trapped air to faulty pressure conditions in the heating system.

Air in the heating system: This can easily be solved by bleeding the radiator. All you need is a common bleed key, a bowl, and rag to catch any leaking heating water. If the radiator still does not heat up properly or the room temperature does not rise, check point 2.

Thermostatic valve: If the thermostatic valve has not been operated for a long time, the pin of the valve may jam. As a result, the right quantity of water no longer flows through the radiator and it only gets warm at the top. In this case, we recommend calling a specialist installer. They can remove the thermostatic valve and change the thermostat if necessary.

Hydraulic balancing: If the hydraulic balancing has not been carried out properly or if the heat supply in the building has changed due to structural measures, this can lead to the radiator only heating up at the top. If this is the case, we once again advise you to contact a specialist installer.

The problem can be resolved by using a Kermi radiator with x2 technology, which causes water to flow through the front panel first. The front panel becomes uniformly warm and the rear panel serves as a shield against the cold outer wall during partial load mode (90 % of the heating period).

Further information on our therm-x2 radiators. To find a specialist partner near you, please refer to our overview.

Heat output

The heat output of a radiator depends on various factors, such as the flow temperature, the size, and the design. If, for example, the flow temperature is very low, a larger radiator should be selected but there are also radiator versions that deliver considerably more output for the same size. The different versions are divided into the following types: 10, 11, 12, 20, 21, 22, and 33. The larger the number, the deeper the radiator. The first digit always indicates the number of heating plates and the second the number of convectors.

You can find the exact heat output of our radiators in the technical information for the relevant product in our download area. When determining the heat output, make sure you select the temperature pairing correctly. Determination of the standard heat output according to EN 442 is based on temperature pairing 75/65/20 °C. In practice, lower temperatures are commonly used nowadays.

Please contact your specialist installer for a precise calculation.

heat recovery

Heat recovery describes the process of making energy reusable. Let’s take the ventilation system as an example. Here, the thermal energy of the extract air is emitted to the outside air via a heat exchanger. The proportion of heat recovered is expressed based on the degree of heat recovery or the amount of heat made available (efficiency).

Heating load

The heating load of a building specifies how much thermal energy needs to be introduced into the building to achieve the ideal indoor climate despite the losses that are bound to occur – e.g. through doors and windows.

Hybrid system

A hybrid system is one that combines different heat generation technologies. Classic energy sources such as oil or gas are frequently linked to renewable energy sources, thereby allowing the strengths of two different heating systems to be combined.

Hydraulic balancing

To ensure that the heating system works without any problems, the volume flow of the heating water needs to be adjusted to the heat demand of every individual radiator. Kermi valve radiators are preset at the factory according to the standard heat output of the radiator. This saves energy costs and ensures optimal thermal comfort. Further information on valve technology & hydraulic balancing.

iF Design Award

The jury of the International Forum Design in Hanover is a panel of experts from all over the world. Every year, they honour everyday products that stand out from the crowd because of their form and function with the iF DESIGN AWARD – one of the most important and prestigious design competitions worldwide. The iF DESIGN AWARD has been around for more than 60 years now. Companies from across the world register their innovative products to participate in this competition. Over three days, an expert jury of more than 50 people undertakes the mammoth task of assessing the 5000 to 6000 products that are competing against each other for the highly sought after award in the category “Product/Packaging”.

Many of our designer and bathroom radiators have already won the prestigious iF Design Award. They include:

Infrared radiator

An infrared radiator is an electrically operated radiator. It provides a high proportion of cosy and efficient radiant heat. that feels like warm sunshine, quickly and directly affecting the human body as well as any other surfaces it irradiates. The high proportion of radiant heat minimises air movement and dust dispersion. This makes infrared radiators particularly attractive to allergy sufferers.

Kermi Clip

Kermi Clips are used to fix the side covers of the radiator in place. These are included as standard with each radiator that comes with attachable side covers. However, if you need a replacement, you can conveniently order the Kermi Clip online from our Kermi spare parts shop .


The German Reconstruction Loan Corporation (Kreditanstalt für Wiederaufbau (KfW)) is one of the leading business development banks worldwide. With their range of funding programmes, they support developers in various ways, e.g. by assisting them with the purchase of residential property and with energy and resource-efficient construction. Many Kermi products are eligible for KfW funding.

kv value

The kv value is also referred to as the flow factor or flow coefficient and is a measure of the flow of a liquid or gas that can be achieved through a valve. It is used for selecting and dimensioning valves, and corresponds to the water flow through a valve (in m³/h) with a pressure difference of 1 bar and a water temperature of 5–30 °C.

Market incentive programme (MAP)

In order to focus on CO2 savings in the construction industry, a market incentive programme has been in place for almost 20 years. The market incentive programme has been updated and widely extended as part of the Climate Protection Package 2030. This subsidy programme creates incentives to generate heat from technology based on renewable energies. This includes, for example, installing heat pumps, replacing old oil heating systems, or using hybrid systems.

Mesh wireless network

In the case of a standard wireless local area network, the reception is distributed throughout the home by an individual device: the router. By contrast, a mesh network is established by placing various access points all around the living area.


A modulating (power controlled) heat pump can adapt its heat output to the heat demand of a building. This allows the heat pump to work more quietly and more efficiently, and optimally adapt to different outside temperatures.

One-pipe system

With the one-pipe system, the flow and return are connected to the same line. This means that the water first flows through the first radiator and heats it, then it continues to flow into the second radiator. The return temperature of the first radiator in the line is therefore the flow temperature of the second radiator, etc.


As an end customer, you can purchase our products from your qualified specialist installer. They will be glad to draw up a quotation for you.
To find a specialist partner near you, please refer to our overview.

In addition, you will also find spare parts and accessories for your radiator or your residential ventilation in our Kermi spare parts shop , which you can order online from the comfort of your own home.

Outside air

The air that flows in from outside.

Paint repairs

You can use our touch-up pen or our spray can to repair minor paint damage to radiators. Both are available in the colour RAL 9016 (White). You can buy these products from your qualified specialist installer, from specialist wholesalers, or can order them online from our Kermi spare parts shop from the convenience of your own home.

Passive cooling function

A building can be cooled with the passive cooling function. During passive cooling, the compressor of the heat pump does not run. Circulation pumps merely ensure that the thermal energy is transferred from the building to the ground via heat exchangers. Passive cooling is not possible with an air/water heat pump.

Passivhaus Institut (PHI)

The Passivhaus Institut is an independent research institution founded in 1996. They test and certify buildings and components which are intended for converting a house into a passive house.

Passivhaus Institut (PHI)

The Passivhaus Institut is an independent research institution founded in 1996. They test and certify buildings and components which are intended for converting a house into a passive house.

Plug & Heat principle

The Plug & Heat principle describes a really straightforward installation process that is particularly associated with air-water heat pumps: Simply put them in place, connect them, and get heating straight away.

Plus X Award

The PLUS X AWARD is the largest innovation prize in the world for technology, sports, and lifestyle. It recognises brands for the quality and innovative edge of their products. That is why we are very proud of the fact that our product series of Kermi therm-x2 steel panel radiators won the PLUS X AWARD for its excellent properties. These include:

  • therm-x2 Profil
  • therm-x2 Plan
  • therm-x2 Line
  • Verteo
Power-to-Heat (P2H)

The Power-to-Heat function of heat pumps allows the use of excess photovoltaic electricity, for example. Power-to-Heat means the conversion of electricity into heat.

Radiant heat

Radiators can emit convection or radiant heat. Convection heat rises in the room, heating the air and moving around within it. In contrast to that, radiant heat does not heat the air directly but heats the objects in the room and the walls. As a result, almost no dust is stirred up and the emitted heat creates a really cosy feeling.

radiation shield

The purpose of a radiation shield is to reduce heat radiation to the facade. The material plays only a minor role here. The important thing is to create an additional air shaft between the radiator and facade, and to allow the heat from the radiator to enter the room unimpeded. You will also find fixings for the radiation shield online in our Kermi spare parts shop.

Radiator type

Steel panel radiators can be divided onto different types. The various types are: 10, 11, 12, 20, 22, 30, and 33. The designation depends on the number of heating plates and convectors installed and thus also on the depth. The first digit indicates the number of heating plates and the second the number of convectors. This means, the larger the number, the deeper the radiator.


RAL is a German institute for quality marks and labelling. It awards what are known as “RAL quality marks” to products and services of particularly high quality in various categories. However, RAL is best known for its RAL colour system, a colour identification system developed by the RAL Institute. Kermi also has a wide range of radiator colours available, which includes almost all RAL Classic colours. You will find more information on this in our Kermi colour concept.

Red Dot Award

The “Red Dot“ award is globally recognised as a seal of quality for good design. As the field of design is so diverse, the award is divided into three disciplines to enable a proper assessment: the Red Dot Award: Product Design, Red Dot Award: Brands & Communication Design, and Red Dot Award: Design Concept. Each of this competitions is held once a year. The Red Dot jury evaluates the submitted products, brands, and communication projects, as well as design concepts and prototypes.

The Red Dot Award: Product Design, whose origins date back to 1955, identifies the best products of each year. Manufacturers and designers from all over the world can enter their designs for the competition in around 50 categories. In keeping with its motto of “In search of good design and innovation“, the Red Dot Jury evaluates all the entries and only awards the Red Dot to products which truly demonstrate good design quality. (Source: www.red-dot.org)

Replacement radiators

Conversion, renovation, and modernisation projects are another area where Kermi offers a whole host of different options. Our replacement radiators are available in designer and steel panel versions and in a range of different heights, lengths, and depths. Suitable hub distances of 500 and 900 mm mean that old DIN radiators can be replaced quickly, easily, and cleanly with new radiators that fit perfectly.
Our replacement radiators are currently available for the following models:

Restoring force

Restoring forces are the forces which act on a pipe in the underfloor heating to return it to its original shape. Low restoring forces and high flexibility are advantageous for underfloor heating systems.

Return temperature

The return temperature specifies the temperature of the water after it has passed through the heating circuit.


“Safety Extra Low Voltage” (= SELV): a low electrical voltage which ensures a high level of connection safety, as it offers special protection against electric shocks.

Serial flow

Kermi revolutionised heating with serial flow and its x2 technology. First of all, the front panel of the radiator heats up to deliver heat quickly and provide maximum comfort. In partial load mode, this is usually sufficient to meet the heat demand. The rear panel acts as a radiation shield. As the heat demand increases, the downstream panel is also heated up and then ensures max. heat output from the radiator.

Smart Grid

The Smart Grid Ready label is awarded to heat pump series that have control technology which allows the heat pump to be connected to an intelligent power grid via defined interfaces. All Kermi heat pumps have been awarded the SG Ready certificate.

Sound pressure level

The sound pressure level specifies the strength of a sound event which is received. This value is always tied to the distance or range, as well as the spatial environment.

Spare parts and accessories

Should you need any spare parts or accessories for your radiator or residential ventilation system, our products can be purchased from your nearest qualified specialist installer. To find a specialist partner near you, please refer to our Specialist partner overview.

In addition, you will also find a selection of spare parts and accessories in our Kermi spare parts shop , which you can order online from the comfort of your own home.

Summer bypass

The summer bypass function cuts out the heat exchanger phase. This means, for example, that the cool night air can be conveyed into the house at the height of summer without it being heated up by the extract air.

Supply air

The supply air is the temperature-controlled (treated) and filtered air that flows into the living space.

Thermal resistance

Thermal resistance is an important factor for assessing the insulating properties of a building component. The higher this value, the better the insulating properties of the building component concerned.

Thermostatic sensor head

Thermostatic sensor heads don’t have to be dull and visually unappealing. Kermi offers a range of designer thermostatic sensor heads – in Chrome, in Chrome White, or with a Stainless Steel look – to complement your radiator.

As an end customer, you can purchase our products from your nearest qualified specialist partner. In addition, you will also find our designer thermostatic sensor heads in our Kermi spare parts shop , which you can order online from the comfort of your own home.


To make it easy to lay the x-net underfloor heating, there is a special unrolling unit (centre-pull feeding). This ensures that the pipes can be unrolled quickly without twisting and can then be laid. This allows work on the construction site to be carried out quickly and without any complications.

Two-pipe system

The two-pipe system comprises separate flow and return pipes. This means that all radiators can be heated evenly – also with the help of hydraulic balancing.

Valves and valve inserts

Valves can be used to control the flow rate of the radiator in accordance with the measured temperature in order to control the set temperature or keep it constant. The further the valve tappet is pressed into the valve, the lower the flow rate of heating water, and vice versa.

What should you do if the valve stops working?
When radiators are not used for a long time, the valve tappet can get stuck due to deposits. It often helps to remove the thermostatic sensor head and to move the tappet several times. In many cases, the problems can be avoided by turning the radiator thermostats to position 3 in empty homes. The valve is then kept continuously in motion and no deposits can form. In some cases (heavy incrustation), the only alternative is to replace the valve insert. Once again, care should be taken to avoid periods of valve inactivity. Note: Valves should only be replaced by a specialist partner!

What should you do if the valve is tapping?
If the valve is making a “tapping” noise, it suggests that the feed and return on the radiator have been mixed up. You can check this by allowing the radiator to cool down. If everything has been connected correctly, the pipe pointing to the middle should get warm afterwards when the valve is left open. If this is not the case, then a reverse manifold needs to be installed. So if your radiator is not heating up properly and you can hear a tapping noise, please contact your local specialist installer.

Where can I find information on valve inserts?
You can find out everything you need to know about Kermi preset valves in the pocket-sized practical valve guide (insert link here).

How do I replace valve inserts?
Valve inserts should always be replaced by a specialist partner to ensure that your radiator continues to work properly. Please contact your qualified specialist installer about this. Relevant spare valves are also available from them.

Window boxes and window sills

Special fixings for window boxes are available for use on steel panel radiators, convectors, and Kermi Decor. For details of the fixings, see the technical documents for the respective product. We do not supply the actual window boxes or similar covers.

You will also find fixings for window sill supports online in our Kermi spare parts shop.

x-center base

With the central x-center base station from Kermi, you can conveniently control and easily manage all components of the “Kermi x-optimised system” via a PC or tablet, e.g. the electric heating rod on the bathroom radiator, heat pump, ventilation, underfloor heating, or radiators, at home – or while out and about too. Other products by different suppliers can also be integrated via the universal EnOcean interface, e.g. switch actuators, window contacts, blinds, detectors, sensors, and switches.

Have a look here to easily see which products are compatible with the x-center base.


The German Sanitation, Heating and Air Conditioning Association (Zentralverband Sanitär Heizung Klima, ZVSHK) is a professional organisation, trade association, and body representing the interests of the plumbing, heating, and air conditioning (SHK) industry in Germany. (Source: ZVSHK)