Maximising efficiencies

The condensing boiler is a highly effective yet affordable technology that is key to raising the efficiency of our energy inefficient buildings. James Porter, Sales Director at Remeha Commercial, looks at the benefits of this high-performance technology to building operators and how to achieve its full potential savings

Buildings are big users of energy, with non-domestic buildings alone accounting for 18 per cent of the UK’s total carbon emissions, according to the Carbon Trust. If the UK is to achieve our legally-binding carbon reduction target of 80 per cent by 2050, it is critical that we engineer wherever possible to raise the energy performance of our built environment. This means constructing buildings that require less energy to run and raising the building performance of our existing building stock.

Refurbishing our past

With new build development representing just a fraction of our total building stock, the real challenge lies in improving the efficiency of our existing buildings. The UK has the largest proportion of old and inefficient buildings in Europe. But knocking them all down is obviously no solution to the problem! In fact, both the BRE and the Carbon Trust estimate that 60 per cent of the buildings that will stand in 2050 have already been built. Unlike the ultramodern, futuristic cities that we might picture in our imagination, the cities of tomorrow will, in all likelihood, look remarkably similar to the ones we live in today. So if we are to meet our steep targets and create a more sustainable future, we must look to refurbishing our past. Refurbishment, whilst admittedly perhaps not the most sexy option for building operators, is nevertheless the most practical, affordable approach to raising the efficiency of the UK’s notoriously energy inefficient buildings and delivering our environmental commitments.

High performance condensing technology

Of all the services, heating is the largest single-end user of energy in a building. And where heating is concerned, the cost-effective retrofit technology offering the most rapid, significant energy and carbon savings is the high-efficiency condensing boiler. The high performance of condensing boilers is underlined by the Energy-related Products (ErP) Directive for heating and hot products that came into force this September. In essence, the higher heating efficiencies required by the ErP Directive now make it mandatory to install high-efficiency condensing boilers below 400kW on both new build developments and existing heating and hot water systems.

For building operators and managers keen to reduce their carbon footprint, condensing boilers not only deliver in terms of efficiency and reliability, they are also quick and easy to install. Now even more compact in design, many of these smaller, lighter boilers are delivered on wheels whilst some manufacturers even offer models that can be dismantled into parts – all of which makes for easier access into the plant room with reduced labour costs and minimum disruption time.

Why waste when you could save?

Some boilers that are between 10 to 15 years old operate at just 50 per cent efficiency. In other words, half the energy input is wasted up the flue. High-efficiency, fully-modulating condensing boilers, on the other hand, offer gross efficiency figures of up to 98 per cent. So replacing any inefficient boilers with modern condensing boilers can literally transform the energy performance of a building.

The Carbon Trust estimates that organisations stand to achieve energy and carbon savings in the region of 30 per cent simply by retrofitting condensing boilers. And this is a conservative estimate: our own data points to savings as high as fifty per cent dependant on the building and the existing heating system in place. This huge potential for rapid savings is particularly relevant to UK organisations as commercial boiler plant continues to provide the heating for a significant percentage of our non-domestic buildings.

Achieving the highest potential savings from condensing boilers

So how do condensing boilers work? Condensing boilers are capable of achieving between 10 to 12 per cent higher efficiencies than non-condensing boilers due to their ability to recover both the sensible and latent heat from the flue gases, energy which is otherwise wasted by conventional boilers. However, even with condensing boilers there can be wasted energy, particularly on old heating systems. This is because condensing occurs when the flue gases are at or below their dew point, which occurs around 54°C. For continuous condensing to take place, the boiler return water must be at this temperature or lower or the higher efficiencies will not be achieved. For this reason, many older heating systems sized on higher flow and return temperatures, typically 82/71°C, will prevent condensing boilers from fully condensing and achieving the maximum energy savings.

If we are to achieve the maximum savings from condensing boilers, we must operate them in such a way that they achieve their full savings potential.

Smart design

To maximise continuous condensing, we should design the heating system to promote lower return temperatures where possible. Consider also installing boilers in cascade operation and adding a sequential control as this will improve the modulation of the boilers and help avoid energy waste. Condensing boilers installed on a cascade or skid system can match the heat output demand more accurately and more reliably for greater energy savings and in a fraction of the space.

Get in control

Adding the appropriate control is critical to the performance of the boilers. Controls can help boilers operate at lower temperatures and at part load, maximising condensing to achieve higher efficiencies and greater savings. The minimum control strategy should encompass valved zone control, thermostats and timers. Where possible, add weather compensation controls as these help the heating system adjust to changing outside temperatures and match more accurately the heat demand of the building. Not only does this reduce energy consumption, but it helps create a more comfortable and productive working and living environment.

Controls can be used to improve both the performance of a boiler and of the entire heating system. A well-designed building management system will integrate the equipment in a multi-component heating system to optimise overall seasonal efficiencies. Controls can lift efficiencies by between 10 and 12 per cent while simultaneously increasing the efficiency and life span of the heating equipment.

Recover otherwise wasted energy

Utilising boilers that incorporate passive flue gas heat recovery (PFGHR) devices is perhaps the simplest, most effective means of achieving full-time condensing on older heating systems sized on higher flow and return temperatures. The energy that would otherwise be wasted up the flue is recovered by the PFGHR unit and transferred back through a Plate Heat Exchanger (PHE) for space heating or cold water pre-heat. This means that full-time condensing boilers are able to use the energy input more effectively and operate at 100 per cent efficiency regardless of flow and return temperatures or boiler load.

Investing in a full-time condensing boiler brings an additional benefit to building operators and managers: reduced pluming. By lowering the dew point of the boiler flue gases, PFGHR technology effectively reduces the nuisance of the white vapour plume produced from the flue, helping comply with the Clean Air Act.


For all condensing boilers as for all heating technology, it is important to ensure that sufficient time and budget is allocated for careful commissioning. This important stage is often the part that is skimped when projects run over budget, yet it is crucial to ensuring high performance, reliability and maximum efficiency from the heating system.

A condensed argument

The more energy we generate, the larger our fuel bills and the more harmful greenhouse gases we emit. Energy efficiency, often referred to as the first fuel, is the answer to our current energy trilemma, as by using energy more effectively we can help slow climate change, improve our national energy security, and reduce our energy costs. Organisations are being encouraged to join the energy efficiency movement through increased legislation. The benefits are clear: lower running costs assist organisations in keeping within their tight budgets whilst the reduced carbon footprint helps meet environmental commitments.

Where heating is concerned, condensing boilers are a practical, affordable solution to raising the performance of our energy inefficient building stock, bringing minimum disruption to an organisation’s day-to-day operation and making minimum dent in the financial coffers.  Pioneers of condensing technology, we at Remeha Commercial already have the products, now we look forward to supporting specifiers and contractors with our expert knowledge to help optimise thermal efficiencies and deliver the maximum savings.

This article originally appeared in Energy Manager magazine.

For more information, email us at


Related Industry News