Condensing boiler

A condensing boiler is a boiler for hot water heating, which uses the energy content (calorific value) of the fuel used almost entirely. With condensing boilers, the flue gas is cooled as far as possible and thereby the heat of condensation ( = latent heat) of the water vapor contained in the flue gas ( and to a lesser extent other vapors) used for heat supply.

Depending on the fuel type, combustion temperature, oxygen content and other factors produce different substances during combustion. If the exhaust gas cooled below the flue gas dew begin to condense the condensable substances.

However, the exhaust gas remains wasserdampfhältig, only a deeper cooling leads to further capture and make better use of the condensation energy (more on this in flue gas condensation).

• 4.1 Hydraulic balancing
• 4.2 Influences on the return temperature
• 4.3 condensing boiler with modulating the power

• 7.1 Determination of the utilization of condensing technology
• 7.2 Verification by the chimney sweep ( Germany ) / cost advantages
• 7.3 condensing boiler and thermostatic valves on the radiators

Origin of the water vapor

The water vapor in the exhaust comes either

• From the hydrogen atoms of hydrocarbons and other organic compounds from the combustion (oxidation) reaction with oxygen to form H2O;
• Or from the product moisture content of the fuels (such as petroleum, palm oil, natural gas, biogas, firewood, wood pellets, coal, freshly slaked coke, grain (see grain combustion ) stale bread, other biomass, waste), which is currently in Kleinfeuerungsbereich mainly only condensing boiler for gas heating oil heaters and pellet can be found on the market.

The higher the hydrogen content of the fuel, the higher the amount of water vapor contained by the combustion of the fuel in the exhaust gas. Condensing boilers are capable according to their quality and to use a more or less large proportion of the heat of condensation depends on the operating conditions ( using conventional boilers and heat losses due to higher exhaust gas temperatures have ).

In the combustion of methane arising from a molecule CH4 a molecule of CO2 and two H2O molecules, from one mole ( approximately 16 g) CH4 thus produces two moles ( about 36 g) H2O, or about 2.25 times the mass of water (vapor). In the reaction of C to CO2 and H2O from H to energy is released, the " crack " of the CH4 molecule has low power consumption (both derived from the standard enthalpies or Standardverbrennungsenthalpien tabular detected ). The low moisture content in natural gas is negligible, the moisture not in solid fuels. The main quantity of water produced by the combustion (oxidation) of the hydrogen atoms of the fuel. During the combustion langkettigerer (usually liquid ) hydrocarbons ( take the example octane C8H18 ) is the ratio of heat energy delivered carbon atoms to the water vapor resulting hydrogen atoms increases, so that correspondingly less water vapor ( per mass ) is formed.

This is the reason why ...

• The water vapor dew ... (because of its higher hydrogen content ) is present in the flue gas from the combustion of natural gas at about 59 ° C and in the combustion of fuel oil at about 48 ° C (values ​​are " about " because natural gases and fuel oils variable compositions have ). The dew point of combustion of the wood, depending on the moisture content of between about 20 and 60 ° C
• Natural gas condensing boilers ... utilizing condensing at higher flow temperatures than is possible when using fuel oil condensing boilers,
• Natural gas condensing boiler ... more generate condensate as fuel oil boiler (for cooling the exhaust gas, for example, to 40 ° C)
• Natural gas condensing boiler ... more Condensing based effect supply to the heating value than fuel oil condensing boiler
• Losses ... the latent heat in conventional boilers the combustion of fuel gas at a maximum of about 11 percent of the energy value, the burning of fuel oil from a maximum of about 6 percent.

The water content is also the reason why green, freshly cut wood has a lower calorific value than dried wood as much heat energy in the resulting water vapor is bound. With condensing boilers wood could also be efficiently burned more humid, if not the heat sapping drying of the wood in the stove would reduce the temperature of the combustion and the resulting fuel gas. This usually leads to incomplete combustion and increased problems with the condensates and soot up the chimney.

History

The first condensing boilers have been developed by Richard Vetter (1982 series ripe for gas in 1984 for oil) and are now commonplace when a new boiler is to be installed.

The gas - fired condensing boiler technology is considered full since the early 1990s as prior art. The oil condensing technology has prevailed since the mid- 90s. These were at first rather smaller companies such Bomat or ROTEX, which relied on the condensing technology. The industry giants such as Viessmann and Buderus moved to first, as more and more oil condensing technology was demanded in the market. The first mass-produced gas - fired condensing boiler series FSM -RK in 1978 from gas heat Institut in Essen ( Mr. SLICK, today DVGW) tested and approved. The power range was 130-1000 kW. The first condensing boiler " with gas burners without fan " was introduced in 1980 by the Gas Appliance Company ( GGG) from Bochum to the International Sanitary and Heating Fair ( Frankfurt am Main). The power range was 8-20 kW.

Technology

The use of the heat of condensation of water vapor in the exhaust gas improves combustion efficiency. This reduces the consumption of fossil ( = finite ) Fuels (keyword "energy saving" ) and the emission of CO2, acidifying gases and other condensable compounds (see below).

The waste from the combustion condensate is acidic and therefore attacks base materials (the composition of such condensates is shown in detail in condensate (heating technology) ). Previously used materials boiler and chimney pipes were this not corrosion resistant enough. By construction, the boiler condensation in the boiler was therefore deliberately prevented what only with high boiler water temperatures (> 70 ° C) was possible. A subsequent condensation in long chimneys would have the sooting causes, so efforts were made not to fall below an exhaust gas temperature of about 120 ° C.

Since the cooled flue gases no longer heat the chimney Brennwertfeuerungen, but their condensables in the " cold " chimney ( like a through-flow cooler acts ) condense, an old chimney must be rebuilt when installing a condensing boiler. To an acid-resistant tube with a non-absorbent, non-porous surface retracted ( made ​​of heat resistant polypropylene -S to 120 ° C, PTFE to 160 ° C or a pressure- sealed stainless steel tube) into the chimney, through which the exhaust gases are led to the outside. In new buildings and chimney pipes with acid resistant ceramic coating can be used. If this tube is not installed in old fireplaces, moisturizes the chimney. This can result in serious damage to the masonry by itself.

On the inner wall of the tube, the density of the exhaust gas condensates run back down and are derived together with the condensate from the heat exchanger. The acid contained can be neutralized by suitable means and the entire condensate can then be passed as part of the statutory provisions in drains or receiving waters ( waters) or collected in some other way.

Thus, in addition to the utilization of condensing technology additionally prevents condensable compounds can be deposited with the condensate and dust pollute the air and reach the acidic components in the atmosphere and fall as acid rain.

If the condensing effect of an installed condensing boiler not used in heating systems with a higher return temperature ( heating systems ) because the heating return the flue gases will not cool down deep enough, different solutions can be used:

• With an air exhaust system (also LAS LAS pipe or chimney system called ) is the necessary for combustion, fresh air drawn in counter-current flowing through the flue gases heated. The hot exhaust gases are discharged through the inner pipe of a pipe -in-pipe system, thereby heat is transferred to the cooler, through the outer tube of the LAS supply system of the burner run. The exhaust is also deprived of energy by heat exchange or by condensation of water vapor. As a result, even at reflux temperatures above the Rauchgastaupunktes of the respective fuel condensation heat is used and is a condensing operation possible. The returning the flue pipe condensate is passed through the heat exchanger in the heater and its heat can there also exits. Such heat exchangers are made of high temperature resistant polypropylene, stainless steel, Teflon, or other materials, the systems usually require premarket approval.
• The aforementioned full condensing boiler heat the intake air not like the LAS system in the fireplace, but in the boiler.
• The normal heating return downstream additional low- temperature heating systems or coils with large inner diameter. There can be accurately dispensed and used the heat that would otherwise be unused passes through the too little cooled flue gases in the chimney / in the environment. Such residual heating system is suitably laid in otherwise unheated lasting cold rooms. So about a cellar, a stairwell or the fresh air can be heated or a winter garden ( qv) or the garage from freezing.

The systems in which the fresh air is heated, save the unused residual heat energy; Systems, so that heat cold rooms, use this latent heat energy.

The exhaust gas can in the above-mentioned Process to be cooled down up to as far as it corresponds to the temperature of the coldest medium throughout the heat exchange process:

• Outside the heating season in the summer, the coldest medium of the drinking water supply will be, ie the temperature of the inflowing cold tap water (which the circulating boiler water cools ) or return increase the circulating boiler water itself
• At low flow temperatures, such as low temperature heating systems or in the transitional period ( spring and autumn ) when the heating system with low power or low supply temperatures is operated at part load, either the heating return or the fresh air or the occasional drinking water supply is the coldest medium.
• At high return temperatures is quantitatively significant, the cold fresh air, the colder medium represents less ( because of the lower compared to the heating demand hot water extraction ) of the cold water inlet. High return temperatures occur mainly at high-temperature heating systems ( radiators),
• In the cold winter at high flow temperatures to quickly bring so heat in the rapidly be cooled rooms,
• In closed radiator valves,
• With insufficient hydraulic balancing of heating system.
• During the heating of a hot water storage vessel: Too frequently occurring reheating of cooled buffer (at low temperature differential ), the circulating boiler water have a high temperature.

Accordingly, the condensing effect can not be used to the maximum in every season, praised optimal saving effects are therefore put into perspective.

Low-temperature heating systems ( floor heating, wall heating, baseboard heating, etc.) result from the outset been a lower return temperature below the dew points possible. The energy gain when upgrading from a normal condensing boiler on a full - condensing boiler or LAS system is therefore lower in these heating systems, since that only the low energy levels of the already well cooled exhaust gas can be used. The economy with upgrading one should be proven for such applications by the manufacturer. The financial cost to take advantage of the last heat of the exhaust gas may pay for itself after a long time, ie that this capital outlay possibly better in energy saving techniques is effective in which it could pay for itself quickly.

Exhaust system

Because of the low exhaust temperatures of the chimney effect in the deduction is only weakly present. Therefore, many condensing boilers have installed an exhaust fan ( ID fan ). This is to ensure the safe withdrawal of the exhaust gas, this system must be as moist as acid - insensitive.

Upon heating, the supply air expands as a gas from the volume increases, it results in a vacuum, so the exhaust, now with lower density increases due to the natural convection in the fireplace on ( this is called the natural chimney draft ). However, because the cooling to condense again reduced the volume and buoyancy or stack effect negates, condensing boilers must be equipped with an induced draft fan that pushes the exhaust gases out of the fireplace.

There are installation situations and locations in which as little back pressure is present on the fireplace that the condensing boiler work without exhaust fan. Therefore, some manufacturers offer devices even without exhaust fan.

Load and return temperature independent boiler

Cousin had the idea to condense the water vapor contained in the exhaust in a separate plastic heat exchanger. The prerequisite is that the exhaust gases have been cooled to about 65 ° C ( otherwise the plastic deformation ).

In plastic heat exchanger then the exhaust gases are further cooled and so necessary for the condensation temperatures below.

The fresh air required for the combustion process cools on its way to the burner and the heat exchanger warms up. The heat energy is retained in this manner in the system and not be lost with the waste gas. The colder the incoming fresh air ( for example in winter), the better the efficiency, because then the exhaust gases are cooled more.

Because the plastic heat exchanger is sensitive to the sulfuric acid contained in the condensate, the amount of sulfur contained in the fuel does not matter. Oil fired boilers can therefore also burn sulfur-containing fuel oils.

By this arrangement, the energy value is neither load nor return temperature dependent in these boilers. Such boilers can also be used as, where pre-and return temperatures between 90 ° C and 60 ° C must lie. They are called high-temperature boiler or " full condensing boiler ".

Load and return temperature dependent condensing boiler

Other designers have taken up the idea, but to take advantage of other opportunities. For them, not the fresh air required for combustion is heated by the exhaust gases. Instead, the standing of the condensation energy is available directly transferred to the heating water.

The condensing efficiency is achieved that return temperature ( = the inlet temperature of the heating water in the boiler ) is lowered so far that the dew point of the exhaust gas falls below the heat exchanger surfaces.

This can be done depending on the design in the boiler itself or in a separate and downstream heat exchanger. The boiler (with internal condensation ) or the heat exchanger ( at downstream condensation) must be acid- resistant because of the resulting condensate.

By this arrangement, the energy value is overload and return temperature dependent. These devices should therefore be used in systems where return temperatures are low, eg for underfloor heating (<30 ° C) or the duration of condensation temperature is high. Usually only a partial condensation occurs here because, although the return temperature is below the dew point, the exhaust gas temperature but above. This is known as a low-temperature boiler.

Necessary changes / requirements of heating systems

In principle, condensing boilers can be used in any heating system. However, the condensate discharge must be ensured, that is, the boiler must be connected to the sewage drain. A manual drain is due to the accumulated amount of water is not practical - not even for family homes. Condensate may be directed in most cases without neutralization only in the drain .. Whether the condensing effect is used, can only be tested by controlling the amount of condensate ( with compared to fuel consumption). Such control can be achieved by draining of condensate into a calibrated collection vessel ( same with discontinuous Abpumpung ).

In the high-temperature boilers ( see above), the energy value is not load- flow or return temperature dependent. There are therefore no restrictions for either floor - other heaters.

In the low-temperature condensing boilers condensing boiler is on load and return temperature dependent, too high return temperatures destroy the condensing effect. This increase low return temperatures there effectiveness. A combination with correspondingly large-sized heating surfaces, such as floor heating, therefore it is useful, but not mandatory. In general, the existing radiators (eg window replacement) are dimensioned large enough that they have sufficiently low return temperatures for modernization measures for the building. The heat output that needs to make a radiator to the room, also decreases dramatically with increasing temperatures. The less heating energy must be released from the radiator, the higher the return temperature of the radiator.

Hydraulic balancing

It is also important to perform a hydraulic balance in the heating system. Here, the flow quantity of the hot water is limited to the quantity for each heating element which is required to achieve the heating capacity. This will ensure that a close mounted on the heating system radiator, flows back from the warm return water does not raise the return temperature and thus destroyed the condensing effect. A study by the consumer organization demonstrates that in the majority of heating systems no hydraulic leveling was done and in these systems, no satisfactory condensing effect.

Influences on the return temperature

So-called overflow, the (integrated with wall mounted in the instrument ) often right after the circulation pump between the flow and return are installed, open at part load to reduce the pressure. This happens when due to closing thermostatic valves too little water is pumped through the heating system and as a consequence too little heat is dissipated in the boiler and the boiler overheated ( the boiler flow is less than the design flow rate). These relief valves will open themselves up to relieve the pump or to a required minimum water circulation from the boiler ensure thereby lifting the return temperature ( return increase ). This also applies to 4 -way mixer.

Both relief valves and 4- way mixing valve should be closed down or removed with the use of condensing boilers, so the return temperature to the boiler is as low as possible. But particular wall units often have such low water content boilers that heat transfer surfaces to protect a certain minimum water circulation must be ensured by overflow from thermal overload. The minimum water circulation should be as small as possible.

Some manufacturers mean by raising the return temperature that only the temperature of the boiler water is raised in the hottest part of the heat exchanger, so that ( if it is cooled by a burner shuts down the water flowed through the heat exchanger to the excessively cold return temperature) in this section there is no water vapor condensation (which to corrosion, could result in significant Glanzrußbildung to the exchanger surfaces and a total loss of the heat exchanger ) and in this part of the heat exchanger just above the dew point cooling takes place, for the cooling below the dew point of a "downstream " corrosion tighter section of the heat exchanger is then provided.

The problems with overflow valves omitted when connecting the boiler over a low loss header. When using a hydraulic separator is to make sure that the boiler- side flow rate does not exceed the heating-circuit flow in the hydraulic separator. Otherwise, hot supply water would be mixed with the return to the boiler again and raise its temperature, which would reduce the calorific value effect or even negate. The boiler- side flow should be set 10 to 30% lower than the heizkreisseitige flow. The hydraulic separator often increases the consumption costs.

An exchange of a standard circulating pump against a self-regulating circulating pump limits the pump pressure and leads to a power saving as the pump regulates its electrical power as needed yourself. Whistling on the valves due to high pressure are avoided. If no buffer memory, and only one heat generator with little water content installed (for example, gas - fired condensing boiler ), it is still better to reduce the pump performance during the downtime of the burner, so that no heat energy is transported away from the radiators.

If a condensing boiler " improperly operated " ( for example, by connecting it to no low-temperature heating system, or if the return temperature is still too high ), can sometimes be warranted for the entire boiler accounts (you can read in the warranty provisions of the provider ). This is more likely in pellet boilers before, because the resulting fuel at this fine is in addition to carbon black of mineral salts that condense in the area of the heat exchanger or recombine and be deposited where they are dissolved and washed away by simultaneously occurring steam condensate; no steam condensation occurs due to a high return temperatures, the baking of these salts, reducing the heat transfer in the heat exchanger and clog the exhaust gas ducts.

Condensing boiler with modulating the power

Modern condensing boilers have burners and pumps that adjust the performance to the currently required heating load. In the transitional period in the spring or fall or when only hot water is to be generated, the heating load can vary. A device able to modulate the performance of such a short is avoided with timing of frequent switching on and off, and minimizes cooling losses in the intervals between the operation of the burner.

Exhaust gas heat exchanger for retrofitting

Remedy for biogenic fuels can only create a more intense optimized combustion by pre-drying of the wood in the boiler about as in the downward combustion technology. Since there are hardly Sturzbrandöfen with built-in condensing technology on the market, the calorific value of the wood can only be used with an available downstream external exhaust gas heat exchanger for retrofitting.

With such a condensing heat exchanger (possibly in conjunction with a particulate filter or then necessary Abgaszuggebläse ), any old boiler, stove or kitchen stove holzverbrennende be retrofitted, if then the fireplace ( as a "wet fire " ) is adjusted. The new generation of boilers has but on improved regulation and modulation of power, better fuel efficiency and lower heat capacity of the boiler materials ( resulting in lower cooling losses has in burner stand-still ), so a replacement is by a new brand sometimes energetically meaningful.

If biogenic materials are burned insufficient arise many different substances, some of which are reflected in the condensate. This means that the land on which is reflected the condensate - for example on the inside of the chimney - are covered by a sticky, viscous ( insulating ) layer. Heat exchanger should be easily accessible for cleaning, so delicate heat exchanger can not be used behind stoves.

Efficiency and efficiency of the condensing boiler

The efficiency of a device indicates how much of the power used can be used. Efficiencies always provide a snapshot (eg measurement in steady state at 70 ° C boiler water temperature and power) and refer to the ratio of the supplied to dissipated power. For the energetic evaluation of a boiler, however this is not enough, because the so-called standby heat losses are not recognized. That is, the losses will be only considered incurred on the burner is running. The radiation losses at the burner is stopped not go with an example. These are included only in the calculation of boiler efficiency factor.

The firing efficiency, which is reported in the chimney sweep protocol specifies, for example, what proportion of the in the form of fuel to the boiler power supplied after deducting the dry (or sensitive ) gas losses remains. From this proportion should now correctly nor the latent exhaust loss is deducted, which arises because of not or not fully utilized condensation heat of the exhaust.

A complete energy assessment of boilers can be made only by means of the Boiler - use efficiency. The boiler efficiency is the ratio of the particular in a period in the form of fuel energy supplied quantity and the votes from the boiler to the downstream heating mains or the hot water tank useful energy. The type of boiler efficiency factor taken into account in contrast to the boiler efficiency indication of the costs incurred in standby heat losses of the boiler, the place, for example by the release of radiant heat to the equipment during burner shutdown.

For efficiency and utilization degree information whether these to calorific value Hi (formerly NCV) of the fuel used or the calorific value Hs (formerly Ho) must always be given, relate. To the efficacy and efficiencies of boilers that are operated with different fuels, compare suitable only energy- related information, as only this call all the energy contained in the fuel. The theoretically achievable efficiency and utilization levels are for oil - fired condensing boilers at 100 % when using Hs, and 106 % when this was calculated with Hi. With gas condensing boilers up to 100 % with a maximum of 111% with Hs and Hi are achieved calculated.

The calorific specific assessment ignores the latent heat loss ( heat of condensation ).

Also the electric power consumption of a heater is taken into consideration.

A better efficiency than condensing boilers only offer gas-powered heat pumps and gas-fired cogeneration plants, which are only offered to the heating of larger houses, sometimes produce spurious vibration and are subject to faster wear.

When evaluating a condensing boiler as a provisioning losses should in addition to the efficiency of heat generation are taken into account, the heat dissipation of the equipment (boilers, storage, lines) are caused with poor insulation. Deployment losses in data sheets given in percent ( the maximum boiler output, not the annual energy consumption) and are in modern devices in the order of about 0.5-1 %. Reductions in deployment losses can be achieved (3 ° C heating setpoint temperature ) instead of lowering the temperature by two degrees and additional thermal insulation of buffers and pipelines, for example by switching off at night. The standby losses occur only when the unit is in operation or is subsequently cooled, extrapolation to 365 x 24 = 8760 hours standby still results from times when small pilot lights " willingness stopped " and leads to inflated values. The timing of a boiler for heating and resulting Abkühlverluste but can cause significant heat loss, the Einprozentmarke the standby losses far exceed (see boiler # wasting energy ).

With a condensing boiler can at suction of the supply air from the boiler room ( in the basement) other restricted latent heat ( from the drying out of the building moisture when the boiler room is used for drying laundry, bathroom and sauna exhaust air from the controlled living space ventilation) are recovered (see flue gas condensation # energy efficiency).

Notes

50 % of the maximum heat output according to DIN 4701 would often suffice to cover 90 % of the heating demand. To cover the remaining 10%, many (calorific value) are oversized boiler and thus lead to high standby losses.

Determining the utilization of condensing technology

About the amount of condensate can be controlled as well, the condensing boiler utilizes the energy of the fuel used. Under certain conditions, it is even possible to draw conclusions on the overall system efficiency draw. The measurement method over the amount of condensate is inclusive and avoids errors in instantaneous values ​​and subtractions from much larger numbers.

As part of a (limited) field study examined the Consumer how efficient condensing technology in practice actually works. The condensate was this key measure .. 88% of the boiler were natural gas, 9% fired with fuel oil and 3% with LPG. The review of 996 boilers in residential buildings showed that " the potential of the device technology is wasted in the realized total assets often ". The calorific value of the benefit was about a third of the devices acceptable, another third need for improvement was given and the last third of the utilization of condensing technology was insufficient. Weaknesses pinpointed the investigation also in thermal insulation of heating pipes (25 % had no insulation on ), 25 % of the systems were equipped with a counter-productive for the utilization of condensing technology spill, 78% of the plants lacked the hydraulic balancing what these plants for deterioration contributed results.

For oil - fired condensing boilers fall under the Research Report 601 DGMK of 2002 liters of condensate per liter of fuel oil burned to (ie 0.1 l / kWh), with only a condensation rate of 50 to 70 % is technically and practically possible. At the same efficient gas condensing boilers (ie the same energy- related boiler efficiency), about 1.5 liters per cubic meter of natural gas. The different amount of condensate oil and gas resulting from the different fuel composition. In natural gas, more hydrogen is included so that results from the combustion more water vapor. If in practical operation due to higher Vorlauf-/Rücklauftemperaturen ( in hot water, for example ) does not ensure complete condensation of the water vapor contained in the exhaust gas have gas condensing boiler due to the higher latent heat loss (within 11 percent ) have a lower efficiency ( condensing reference ) on an oil - fired condensing boiler ( max. 6 per cent of latent heat loss).

Review by the chimney sweep ( Germany ) / cost advantages

The inspection interval for gas-fired condensing boilers in Germany is two years instead of at one year, as is customary with most calorific devices. It is performed by Sweeping and Examination Regulations at a condensing boiler does not work after BlmSchV (exhaust gas loss provision), but a recurring action. This check involves determining the CO content in the exhaust gas ( gas analysis ), and an exhaust gas path testing.

This means a significant cost advantage for condensing boilers.

Condensing boiler and thermostatic valves on the radiators

The use of thermostatic valves on radiators or fired wall mounted units with lower water content can lead to the return water flows back to hot, then is the use of the calorific value or the burner clocks ( and the associated willingness losses increase ). Remedy, however,

• Hydraulic balancing of all radiators
• Modulating oil or gas burners that as far downmodulate ( state of the art in 2012 is a minimum 1 kW at Thision )
• As well as intermediate buffer layer with charging technology.

Condensing boiler or low temperature boiler?

When buying a new or replacing an old heating initially impressed with the higher standard efficiency condensing boiler technology over the calorific value technology. However, restrictions must be observed:

• Condensing technology is more expensive to buy. This applies to the boiler / the spa itself, possibly larger radiator and the necessary modification of the chimney ( tube feeding ). If no sewage outlet near present, it must be created.
• In practical use, a condensing boiler quickly unintentionally fall into a quasi - calorific operation, so that the efficiency decreases. The reason for this is usually a too high return temperature of the heating water, for example, created by electronically limited thermostatic valves on the radiators or space by space heater with too low a surface, ie, Oversizing of the boiler or under-dimensioning of the heat consumers. However, even if a condensing boiler the heating value do not always do so, the exhaust gases come but with lower temperatures (in the range 60-80 ° C) from the boiler, as in conventional low temperature boilers (120 ° C)
• When using the same high-efficiency pumps consume condensing furnaces in operation about 30-40 % more power than calorific value structures because the relatively cool exhaust gases do not passively rise in the chimney and therefore must be actively blown off. However, the power consumption was measured comprised 3 % of the fuel consumption in one study, two-thirds of the circulating pump and one-third of the burner, fan and control were consumed. The additional power consumption, caused by pressure drop in the exhaust gas flow rate due to additional heat exchanger surfaces, thereby amounted to just 0.3 % and the ratio of surplus to expenditure - on primary energy level - was just under 7 When considering the energy costs in turn the price of electricity comes into play.
• The residual heat contained in the exhaust gases is generally accounted for as a total loss. But this is true only for the relatively cool exhaust gases of condensing technology, which are actively blown off in a separate acid-resistant pipe with little additional heat exchange through the chimney. This is true only in part, for the warmer gas from a heating value system, because these cool as it rises in the chimney and this heat is transferred to the masonry (where the masonry is a poor conductor of heat and the heat transfer is not as optimal as in a heat exchanger made of a ferrous material ). This heat helps to heat the adjoining rooms, and is not to be regarded as a loss.