Getting the best from replacement boilers

Published:  03 September, 2007

Standard-efficiency boilers could match the performance of condensing boilers in replacement projects — Graham Williamson.

Despite the heating industry’s excellent response to Part L2 and L2a of the Building Regulations, which has seen the move towards high-efficiency boilers gather pace since April 2006, Graham Williamson argues that standard-efficiency appliances still have a major role to play in the non-domestic sector.

Without doubt, the last 12 months have been extremely challenging for everyone involved in the heating industry, particularly installers and specifiers. Not only have they been charged with getting to grips with the complexities of the Building Regulations, but they also had to do this in a relatively short space of time, as the approved version of the Part L document was rushed through to meet its deadline.

The good news is that despite these hurdles, the industry as a whole has embraced energy efficiency. There is now a wide range of high-efficiency commercial condensing boilers on the market that meet and exceed legislation requirements, offering installers and specifiers more choice and options. To complement this, manufacturers and trade-industry bodies have taken the initiative and produced a range supporting information to help installers understand what they actually need to do to comply.

Although there has never been a better time for installers to help their end-user customers take advantage of a high-efficiency heating and hot-water system, it is vitally important they recognise that a high-efficiency boiler may not be the right solution for every application.

Design issues

The fact remains that a high-efficiency boiler will only condense when the system allows it to do so, crucially, when the return temperature is maintained below 50°C. However, commercial and industrial heating systems in UK buildings can be as much as 20 to 30 years old, and many cannot easily adopt condensing technology — either through design or suitability. With the replacement boiler sector accounting for 70% to 80% of all commercial boilers installed, careful consideration must therefore be given to overall system design before choosing either a high-efficiency or standard-efficiency boiler for a replacement project.

So what factors do installers need to take into account before making the right selection for their end-user customers? The main consideration is the flow and return temperatures that commercial buildings are designed on. To maximise the benefit of a condensing boiler, for example, the system must be designed for 60°C flow and 40°C return. However, most of systems are designed on 82°C flow and 71°C return, and if this is overlooked, the rated output of the appliance can significantly reduce by as much as 8%.


Secondly, installers must think more carefully about flue positions. It is critical that the flue system is inspected not only to ensure it is in sound condition but also that its construction is suitable for a condensing boiler. Due to the high level of condensate that will be formed within the flue system, the material used must be impervious to the acidic nature of the flue gases to prevent a serious failure.

Controls also have a significant role to play. Whether you are installing a standard-efficiency or high-efficiency appliance, unless it is managed and operated properly in an appropriate manner, the benefits of even the most energy efficient boiler will be significantly reduced.

There are other factors too that have to be taken into account. They include looking closely at the water-distribution characteristics and, because the mean water temperature is lower in a high-efficiency system, designers also need to consider radiator sizes to meet the heating requirements of a building.

If these factors are not taken into account, a condensing boiler installed into an existing building using traditional design parameters will not deliver maximum benefits. It is for this reason that recognition was given in the Building Regulations (L2B for existing buildings) for the use of standard-efficiency boilers. In fact, by more accurately sizing a replacement boiler (through a system load assessment) and evaluating the controls, a modern standard-efficiency boiler could offer the same carbon-reduction benefits as a condensing boiler.

Relative merits

Standard-efficiency and high-efficiency boilers have their place in the market, and it is essential that installers and specifiers consider the application of these products along with the requirements for installing them in their own right. Building-services managers will then benefit from the most cost-effective and energy-efficient solutions for their premises.

Graham Williamson is business director for commercial heating with Ideal Boilers.

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