Glossary of Terms

Glossary of Terms


The absorber is the part of the solar collector that collects (absorbs) the incoming solar radiation and transforms it into heat.


The absorption specifies the percent of the radiation on the absorber area that is transformed into heat.

Air heat pump

System that uses heat in the air to heat buildings.

Annual efficiency

Important figure for assessing the energy efficiency of boilers. The annual efficiency designates the percentage ratio of the heat energy used to the energy used across the entire year.

Boiler efficiency

Unit of measurement that specifies how much heat can actually be used from a fuel type. For this, flue gas and radiation losses are taken into account.

Bosch Heatronic

The electronic "brain" from Bosch guarantees optimal operation of the heating system and easy operation of the heating appliance.


Mixture of anti-freeze and water to prevent freezing.

Buffer tank

Energy is stored temporarily in the buffer tank which is always necessary if there is an over or undersupply of energy.

Chimney appliance

A chimney appliance draws the required combustion air from the room and requires a chimney to exhaust the flue gas.

Circulator pump

The circulation pump ensures the transport of the heated and cooled liquids within the heating circuit.


Compresses the gaseous refrigerant of the heating pump at high pressure.

Condensing boiler

The condensing boiler cools the flue gases down so that there is condensation of the steam contained in the flue gas. The heated steam is then used for heating.

Condensing technology

The condensing boiler specifies how much heat can be used for the combustion of the fuel. In condensing technology, the steam is condensed into flue gas in order to be able to use the condensation heat.

Conduit principle

Procedure for hot water heating during which the water is heated as it flows through the appliance.


Its task is to regulate ("control") the customer's individual temperature desires for heating and hot water heating. The control can also incorporate other systems such as solar heating systems.

see room temperature-controlled control
see outdoor temperature reset control


Coefficient Of Performance (COP). Ratio of usable energy to energy produced. Ex: CoP4 means that in order to be able to use 100% energy, 25% must be produced with the result that 75% of the energy from the environment is available free of charge.

DHW storage tank

Domestic Hot Water (DHW). A container with heat exchanger for domestic water.

Eco(logical) balance sheet

An eco(logical) balance sheet analyzes the entire life span of a product or process including the associated ecological effects and evaluates the material and energy amounts during the life span and the environmental damage resulting from this.


The effectiveness of a boiler refers to the ratio between its heat output and the input fuel power at a specified time of operation.

see also standard efficiency, annual efficiency

Electric hot water heater

Electrical appliances that generate hot water. They are available as electric tankless heaters, electric storage tanks, or electric mini-tanks.


The escape of solid, liquid or gaseous materials from systems or technical processes that get into the air, water or other areas of the environment.

Exhaust air collector

The exhaust air collector conducts the heat that it extracts from the exhaust air back into the heat pump.

Expansion tank

The expansion vessel serves to collect heating water during the volume change due to the heating up or the release of heating water during the cooling down of the system. Its function is to convey the cooled-off heating water back into the heating system.

Facade mounting

With this type of mounting, the solar collectors are mounted at an angle of 45-60 ° on the facade.

flat plate collector

Device similar to radiant floor heating that is laid in the earth in order to use heat energy from the earth.

Flat roof mounting

With this type of mounting, the solar collectors are mounted on a frame. This variant is suitable for bungalows and garage roofs or for set-up in a garden area.

Flue gas

Flue gases rise, among other things, during the combustion of fossil fuels such as oil, natural gas or coal. Their composition depends on the fuel type. They consist largely of steam and carbon dioxide (CO2). Furthermore, depending on the fuel, they contain additional materials.

Flue gas loss

The flue gas loss is the part of the unused heat that escapes into the outdoors with the flue gas.

Flue gas venting

The vent or chamber conducting the flue gases through the flue gas system (e.g. through the chimney, through the outer wall or directly out of the roof).

Flue system

The part of a heating system that conducts the flue gases into the outdoors. Earlier, chimneys handled this; today, flue gas systems are being used instead.

Gas hot water heater

Appliance for heating domestic water with the pass-through or instant tankless principle.

Geothermal heat pump

System for using geothermal heat for heating homes and buildings.

Geothermal probe

To use heat energy, U-shaped plastic pipes of generally up to 1330 ft. are inserted vertically into the earth. A cold brine (=water alcohol mixture) circulates in the pipes, which takes up the heat from the earth.

Heat exchanger

It transmits the heat generated by the burner to the water in the heating circuit.

Heat pump tank

Tank especially attuned to the heat pump.

Heat pumps

Heat pumps use environmental energy for room heating and domestic water heating. Their functional principle corresponds to that of a refrigerator, however in the opposite direction. The refrigerant in the heat pump circuit draws heat from the earth, the air or water and vaporizes in the process.
Then it is brought to a higher pressure and thus to a higher temperature.
This "heated" steam emits heat into the heating water, whereby it liquifies again. After subsequent pressure reduction, the refrigerant is again present in its original form.

see also geothermal heat pump
see also air heat pump
see also hot water heat pump (not present in MEE)

Heating technology

In contrast to condensing technology, here the steam is not condensed out of the flue gas.

Low-temperature boiler

See non-condensing technology. The same as a heating appliance that utilizes non-condensing technology.

Modulating pump

Characteristic diagram pumps are regulated circulation pumps. They detect independently what quantity of heating water is required and adjust the pump output automatically to the requirement. This saves energy and reduces flowing noises in the pipelines.

On-roof mounting

With this type of mounting, the collectors are fastened on the roof without changing the roof area significantly.

Outdoor temperature reset controller

The supply temperature of the heating water is controlled based on the outdoor temperature. Better said: the colder it is outside the higher the supply temperature must be.

Plate heat-exchanger

In plate-type heat exchangers, the heat is fed into or removed from the water through heat exchange. They consist of wave-shaped molded plates that are put together so that first the water that is to be heated and cooled off flows in each of the series of intermediate spaces.

Primary energy

Primary energies are the naturally-occurring energy sources such as coal, oil, natural gas, solar energy or natural uranium.


Apparent in the air-tight sealed refrigerant circuit of a heat pump, which experiences pressure and temperature changes due to particular components (compressor, expansion valve) and can thus absorb and give off energy.

Renewable energy

Energy sources that are not in decline according to human measurements. These include wood, solar energy and geothermal energy.

Return temperature

The return temperature is the temperature of the heating water used by and flowing back into the heat generator.

Room temperature-controlled controller

The room temperature is controlled by recording the indoor temperature via room temperature sensors.

Solar collectors

Solar collectors have the task of transforming the energy of the sun into heat energy.

Solar combi tank

Tanks in the tank system (DHW tank in the buffer tank) with two heat exchangers (1 for heating appliance, 1 for solar appliance). See solar storage tank.

Solar controller

Controls the operation of the solar heating systems.

Solar heat

This refers to the transformation of solar energy into heat with the help of solar liquid in solar collectors with solar collectors for domestic water heating, heating assistance, and pool heating.

Solar heating system

A solar heating system transforms the radiation energy of the sun into heat energy. Essential components are the solar collectors, the solar storage tank, and the controls.

Solar storage tank

Tank with two heat exchangers in different positions. The lower heat exchanger serves to heat via the solar heating system. The upper heat exchanger is only needed for the heating appliance if the solar radiation is not sufficient.

Standard efficiency

Measure of the usage of the energy in the fuel.

Stratifying tank

Energy-efficient possibility for hot water heating. Here, the hot water is layered into the tank from above.

Supply temperature

The temperature at which the heated water in the heating circuit of the central heati flows from the boiler into the heating areas in the rooms.

Vacuum tube collector

With this especially high-performing collector type, the absorber consists not just of an area, but rather it is put in glass tubes. To prevent heat losses, there is a vacuum in the tubes (thermoscan principle).

Ventilation system

Due to the tight construction of buildings, a natural air exchange is no longer an option. Systems for controlled residential ventilation take on this task and can transmit the energy from the air used to the fresh air. This saves energy.