Condensing boilers for home heating

Saving starts at home

Condensing boilers are heat generators used for space and/or water heating. They can reach higher energy efficiencies than conventional (non-condensing) boilers because they are able to extract additional heat from the exhaust gases that would otherwise be lost and released into the atmosphere.

Condensing boilers have increased efficiencies in the order of 10-15%. Actual efficiency gains are dependent on the installation that is being replaced as well as the required working conditions such as the required hot water or heating system temperatures.

As conventional (non-condensing) boilers, condensing boilers can run on varies fuels. In regions where a mains gas grid is available, natural gas is a logical and cost-effective choice. In rural and more remote areas where the gas grid is not present, LPG is a viable and environmentally sound option. There are also systems available that run on renewable fuels, including (purified) biogas. This offers rural areas the possibility to use locally or regionally available energy sources such as manure and organic feedstock and reduce their dependence on expensive and imported fossil fuels. Condensing boilers are also very compatible with solar heating systems that can increase the overall efficiency of a heating system further and reduce fuel cost.

Installations tend to be more expensive than non-condensing boilers, but because they are more efficient, significant fuel savings are achieved over their lifetime. Typically, savings of 20% are achievable and the additional investment cost is paid back in several years. Condensing boilers are a mature technology; they are widely available across Europe and have become the standard in northern European countries.

General Info

What is it?

Condensing boilers are heat generators used for space and/or water heating with high efficiencies typically greater than 90%1.

What are the benefits?

Low Carbon: A condensing boiler may reduce the energy demand for space heating and warm water production significantly as compared to conventional boiler. These higher efficiencies are achieved by recovering the waste heat that would normally be lost through the flue.

Depending on the system replaced and the type fuel used, condensing boilers can reduce GHG, NOx, PM and CO emissions substantially, especially compared with conventional (noncondensing) boilers and even more compared to electric heating systems.

Efficiency: Installations have higher efficiencies than conventional (non-condensing) gas or oil boilers.

Costs: Depending on the system substituted, condensing boilers can lower energy bills compared with non-condensing boilers and conventional electric heating systems.

How does it work?

Condensing boilers are able to extract extra heat from the flue gases that would normally be lost and released into the atmosphere. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate and is then recovered and fed back into the heating system. This process preheats the water running to the system, thereby lowering the need for extra heat (and fuel) that is needed to get the water up to the required temperature.

Suitability/applicability

Condensing boilers increase their efficiency with low return water temperatures. The temperature of the recovered heat is determined to a great extent by the water distribution system and the type of heat emitters installed in the building. Under floor heating systems or larger heat emitters typically guarantee lower return water temperatures suitable for condensing boilers.

As conventional (non-condensing boilers), condensing boilers can run on varies fuels. In regions where a mains gas grid is available, natural gas is a logical and cost-effective choice. In areas where this is not the case, LPG is a viable and low-carbon option, particularly compared to oil. There are also systems available that run on renewable fuels, including (purified) biogas. This offers rural areas the possibility to use locally or regionally available energy sources and reduce their dependence on expensive and imported fossil fuels.

Condensing boilers are very compatible with solar heating systems that can increase the efficiency of a heating system significantly and further reduce fuel costs. The boiler provides heating in those situations where the heat from the sun is insufficient.

In most situations installations can be sited in the same place as non-condensing boilers. Both have similar dimensions and they are as easy to install. Condensing boilers do require a condensate drain.

 

Condensing boilers cover are able to cover almost all output ranges and come in different sizes and shapes. Wall-mounted units deliver up to 100 kW. Connected one to the other in a cascade system, the output can be increased to several hundred kilowatts. Floor-standing units can supply nominal outputs of more than 10,000 kW.

Detailed Info

Costs, Savings, Earnings

Investment costs are slightly higher for condensing boilers than for conventional ones. Depending on the usage of the system, these higher investment costs are paid back in several years due to reduced fuel consumption (typically -20% compared to older, non-condensing boilers). As heating typically accounts for the largest share of a household’s annual energy expenditures, an efficient boiler can make a large difference.

Condensing boilers do not require subsidies or other support, but in some European countries grants are available that contribute towards the investment. In some countries they are compulsory and the use of non-condensing boilers is discouraged.

Environmental Impacts

Environmental impacts of condensing boilers are lower compared to conventional ones mainly local air pollution and GHG emissions. Environmental impacts are reduced in proportion to the efficiency gain and the reduction of fuel use.

Efficiency

Condensing boilers have increased efficiencies compared to conventional boilers. This thermal efficiency improvement is usually in the order of 10-15%.

Commercial Maturity

Condensing boilers are a fully commercial and mature technology. They are widely available across Europe and have become the standard in northern European countries.

Level of Maintenance

MEDIUM: Installations require similar levels of maintenance as conventional boilers. It is recommended to inspect systems on an annual basis.

Technical Details

The installed thermal capacity of a condensing boiler for domestic use is typically in the range of 6 to 35 kW. Conversion efficiencies may reach 109% (on Net Calorific Value).

Trade associations

Association of the European Heating Industry

www.ehi.eu