Combination heaters
A combi boiler is a compact heating device that is used both for heating water for heating and for providing hot water by means of an integrated flow heater .
Most combination heaters are operated with natural gas or liquid gas and are then called gas combination heaters or gas combination water heaters (KWH). Natural gas and liquid gas devices are almost identical. To convert to the other gas, it is usually only necessary to replace the nozzles and adjust some settings.
In contrast to a boiler , the combustion chamber of a thermal bath is surrounded by significantly less water. Before the introduction of condensing boilers with closed combustion chambers , most thermal baths were equipped with open heat exchangers , which consisted of a pipe register with metal sheets to improve the heat transfer and had a very low water content . Due to the small size of the heat exchanger, thermal baths require little space and can be wall-mounted. In order to avoid the boiling of the water, either a minimum circulation is required or the flame is regulated accordingly.
function
A combination heater usually consists of the burner that fires the heat exchanger (heat exchanger) to heat the water in the heating circuit and a downstream plate heat exchanger in which the heating water transfers its heat content to the drinking water to be heated if required . A classic combination boiler does not have a storage tank for heated drinking water, but works as a flow heater.
The heating circuit refers to a closed circuit that is kept in circulation by a heating pump that is usually integrated in the combi boiler. Radiators (mostly made of copper or plastic ) are connected to the circuit via the heating pipes , which release the heating energy stored in the water to the ambient air and thus warm the rooms.
The instantaneous water heater heats the water for direct consumption. This is why a combination heater is often hung where the most hot water is needed - in residential buildings mostly in the bathroom or kitchen. As with central heating , however, it is also possible to draw the heated water from rooms further away.
The heating function of the combi boiler is usually controlled by a room thermostat , which is usually installed in the living room in a location that is not lit by the sun. The desired room temperature can be set there. Usually there is also the option of defining heating and lowering times . There is also the option of connecting an external thermostat.
The water heater function is controlled via the water withdrawal. If someone takes water from the hot water pipe, the burner switches on and heats the water at full power. However, until the heating reaches the desired strength, it takes some time in which cold to lukewarm water runs through without actually being able to be used.
Differences between combi boilers and gas boilers
In contrast to gas boilers, the combined or gas boilers usually do not have a hot water storage tank. Combination heaters use a so-called flow heater to heat the water when it is needed, while the gas boilers maintain the temperature of the water in the boiler for a long time. The volume of the memory can vary greatly.
Comparison of the combination heaters with separate devices
In the following, the advantages and disadvantages of a combination heating system are listed in comparison to a simple floor heating system and a separate hot water tank or instantaneous water heater .
advantages
- Less space required (the combi boiler is often in the same housing as the same device without a flow heater function).
- Slightly lower gas and water consumption than separate devices because the heat losses are lower in combined operation.
- Lower installation costs because no second gas or high-voltage connection is required for an electrical instantaneous water heater.
- All the advantages that a thermal bath has over a hot water boiler (depending on the system, there is usually less loss of supply if water is seldom withdrawn; less space required).
- Often longer service life compared to electric instantaneous water heaters.
disadvantage
- Under certain circumstances a larger housing, which may be structurally difficult to integrate in the vicinity of the greatest hot water requirement.
- Depending on the system, compared to an electric instantaneous water heater and a hot water boiler, there is usually a longer waiting time until warm water is available (if the system has cooled down and the device does not have an automatic supply function). This is associated with increased water consumption if water flows away unused until the desired temperature is available at the tap.
- When using a mixer tap in the middle position, the thermal baths start unnecessarily even when water is drawn off briefly, although until the tap is closed, only cold water may run out of the pipe. Separate taps for cold water and hot water can help to avoid heat loss due to incorrect operation.
- The price may be higher than when buying individual devices, especially when comparing a combination of a simple gas boiler with an electric instantaneous water heater.
- The high output of the devices required for hot water heating in the flow can lead to high burner cycle rates in heating mode with high heat losses during downtimes (see also Boiler # Energy Waste ).
- With increasing water consumption, the running costs of boilers are often lower. With low consumption, however, the heat losses are more significant.
Combination boiler or condensing boiler
In recent years, (gas) condensing boilers with domestic water heating have clearly overtaken the simple boiler combination boilers in terms of efficiency and sales figures. In 2009, Saxony even introduced a “scrapping bonus” for old boilers .
Individual evidence
- ↑ The designation gas combination water heater (KWH) is used in technical documents such as the TRGI . See also: Gas installation: Tips for practice - terms, data, technical rules , working group for economical and environmentally friendly energy consumption eV, updated edition 2010
- ↑ What is the difference between a boiler and a thermal bath? , In: Kesselheld.de. Accessed May 2020
- ↑ Gas boiler vs. Gas boilers - what's the difference? In: Oekogas.de . October 20, 2016 ( oekogas.de [accessed October 28, 2016]).
- ↑ Gas boiler vs. Gas boilers - what's the difference? In: Oekogas.de . October 20, 2016 ( oekogas.de [accessed October 28, 2016]).
- ↑ Heat generator: Gas condensing boiler from Stiftung Warentest 07/2008, accessed December 10, 2012.
- ↑ "The times of the instantaneous water heater or the combination heater are almost over." Konsument.at issue 10/2003, accessed February 15, 2010.
- ↑ Scrapping bonus for boilers Stiftung Warentest 08/2009, accessed December 10, 2012.