Condensing boilers are the perfect partner

With renewable technologies increasing in stature across the UK, much can be said about the significance of carbon reductions and improved efficiencies. Stefan Gautsch, Design Engineer for Buderus, explains how, despite this trend, condensing boilers still have a part to play in supporting renewables as part of an integrated central heating system.

Over recent years we have seen a number of CO2 saving initiatives brought to the commercial and industrial sectors with the aim of encouraging businesses and private investors to find fuel efficient heating solutions. Whilst the overarching aim of initiatives such as the Renewable Heat Incentive (RHI) and the Carbon Reduction Commitment (CRC) is to contribute to the UK’s reduced emissions targets, financial savings are an added benefit of an investment in low-carbon systems.

A widespread strategy to reduce carbon emissions lends itself to a significant investment in renewable heating technologies, of which there are a variety available in the UK market. Whilst each individual technology has its own associated strengths and weaknesses, one factor which is common across the entire product portfolio is the fact that renewable technologies are not typically manufactured to cater for 100% of a building’s heating demand throughout the year. For example, solar thermal technology can be expected to provide some 60% of the hot water demand over an annual period. The remaining requirement, which is likely to be needed over the winter months, can be provided by the incorporation of a condensing boiler into the building’s heating system.

Added reliability

Essentially, the strength of a condensing boiler is its consistency of performance. A reliance on fossil fuel means that the condensing boiler can provide a constant supply of heat, which isn’t necessarily the case for renewable technologies. As a result, an alternative heat source is required to top-up that extra heat over the winter months when daylight hours reduce and temperatures dip.

Typically, renewable technologies tend to be installed to provide the base load for a building, which in simple terms means the heating load required by the building for the majority of the time. A condensing boiler can then be integrated into the heating system to provide back-up – relying on fossil fuel to provide the heating that the renewable technology is not capable of delivering.

This case is typical where 100% of a building’s load is only required for a small minority of a yearly period – a week for example. In instances such as these, as there are few occasions where the building’s demand is very high, increasing the renewable system to cover peak demand of just a few days is not a cost-effective solution. Consequently, it makes sense to install a suitable back-up boiler which can easily handle peak load requirements. Condensing boilers, such as the Buderus GB312 are a good option thanks to a high turndown rate, which means they have particularly low working points. This means they are capable of operating for extended periods in a part-load condition, whereby their primary function is to offer support for the lead renewable technology.

Despite a reliance on fossil fuels, condensing boilers in general are highly efficient and have the added benefit of low emissions. The technology used by a condensing boiler is such that heat which would go to waste via flue gases in a conventional boiler is used to pre-heat the water entering the system to maximise efficiency. The Buderus GB312 operates at seasonal efficiency levels of up to 96.4%, making it the ideal partner for a renewable heat source, which will guarantee favourable heating efficiencies of its own.


For the new build sector, the favourable emissions levels of condensing boilers are an attractive investment, particularly when it comes to planning permission applications, which can be aided by a favourable BREEAM rating. With BREEAM ratings categorising buildings, or proposed buildings according to sustainability criteria, an efficient source of heating should be a primary consideration for stakeholders. With an increasing number turning to renewable heating technologies, the value of reliable yet efficient support from a condensing boiler is strengthened.

Whilst a condensing boiler is the perfect partner for renewable heating technology, non-condensing oil and LPG boilers are just as suitable, particularly in areas where there may be no access to a mains gas supply. The main consideration should be that the output of the supporting boiler can bridge the gap between the peak load of the renewable technology and the maximum demand from the building at a given time.

As with any dual heating system, it is essential that the technologies used are entirely compatible with each other, with a suitable control system key to the successful operation of an integrated heating system. Today’s range of controls are able to measure the heat demand of the building using a combination of external weather compensation controls and internal thermostats, which can co-operatively determine the output required by the primary and supporting heat sources. The sophistication of the intelligent controls available is such that the system can assess how much output is available from the primary heat source, i.e. the renewable technology, before deciding whether to activate the secondary source, i.e. the boiler, to provide the required levels.

Integrating controls

The Buderus 4000 series of heating controllers has been developed in line with the latest offerings within the industry and can control virtually any heating system, regardless of size. Today’s generation of controls are able to integrate renewable technologies fully without compromising efficiency and can also be calibrated with the Building Management System (BMS), which will ensure that the entirety of the building’s energy using infrastructure is working to its full potential.

The industry has worked extremely hard over recent years to improve the efficiency of its products and the latest condensing boilers and we are now in a position where we can reap the benefits of condensing boilers which operate at close to 100% efficiency.

Given the introductions of the RHI and the CRC, it is encouraging to see investment in renewable technologies across many commercial and industrial applications, however with this comes a need for support. A condensing boiler and a corresponding controls module is the perfect partner for a range of renewable heating technologies.

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