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Are we being misled over boiler efficiencies?



All new boilers must be 92% efficient (or 'A-Rated' on the ErP label). This efficiency can be increased by 1%-5% depending on which heating control is fitted. However studies have found that actual efficiencies are on average 83% for combi boilers and 80% for heat-only boilers. Energy Performance Certificates recommend upgrading a 78% non-condensing boiler in order to improve the energy efficiency banding of our homes, but actual efficiency improvements are likely to be much lower than we expect. Furthermore, if we are consistently 10% out on EPC calculations we are at risk of missing our 2050 net-zero carbon emissions target. In this blog, we explore how we can get closer to factory rated efficiencies and the regulatory tweaks needed to help consumers, installers and manufacturers get this right.


ErP v SEDBUCK efficiencies

Actual efficiencies

Where it went wrong

ErP V SEDBUK efficiencies - what's the difference?

All new boilers fitted into existing properties must have an ‘ErP’ (Energy rated performance) of 92%. ErP is a European Directive that came into force in 2015 and replaced SEDBUK (Seasonable Efficiency for a Domestic Boiler UK) for existing dwellings; the UK’s universal standard for determining boiler efficiency.

ErP rates the efficiency of all energy-consuming goods between A++ and G and this is displayed clearly on the product’s label. 92% efficiency is equivalent to ‘A’ rated.

SEDBUK is still used for boilers in new build homes under the current building regulations and requires a seasonal efficiency of at least 89.5%. SEDBUK is also still used for EPC calculations.

As it happens, all new gas boilers have a SEDBUK efficiency of between 89-90% and an ErP of at least 92%. Boilers that exceed the ErP rating, ranging between 93-94%, still have SEDBUK ratings of 89-90%. In other words, efficiency standards are the same for new builds and existing properties, only the way in which the information was presented changed under the 2015 ErP directive.

The ErP directive also requires whole-heating efficiency labels to be created which allow for uplifts in efficiency based on the heating control used. Eight different classes of control are identified as giving an uplift in heating efficiency of between 1-5%.

The net result is that combi boiler owners will believe they have a boiler with an ErP rating of between 92-94%, paired with a heating control of between 1-5%, offering a combined heating efficiency of between 93-99%.

Calculating actual boiler efficiencies

In 2009, four years after condensing boilers became mandatory, The Energy Saving Trust published its findings following a 12-month field study of 30 A-rated condensing combination boilers and 10 A-rated condensing regular boilers.

The field trial found that the average efficiency was 83% for combi boilers and 80.3% for regular boilers. The difference between efficiencies stated to the homeowner – 93-95% assuming an equivalent basic on/off control is used – is therefore at least 10% greater than the average efficiency in the field.

As the report points out, “The mean of the trial data suggests that the in situ performance of the boilers is significantly less than the rated SEDBUK seasonal efficiency.”


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Current and proposed minimum efficiency standards

Boiler Plus

Under new efficiency regulation Boiler Plus (introduced in 2018) it became mandatory to fit an ‘advanced energy saving measure’ with a new combi boiler and 'time and temperature' controls with boilers that work with a hot water cylinder.

Advanced energy saving measures include weather and load , which offer 3% and 4% efficiency uplifts respectively. However, the regulations were diluted by the inclusion of ‘automation and optimisation’ controls, many of which are essentially forms of ‘smart’ on/off control that add just 1% of efficiency (or 0% according to the 2016 SEDBUK consultation). 

The regulations were further weakened by the incompatibility of many load and weather compensation controls with many boilers. Compensation controls must speak the same language as the boiler to achieve 3-4% efficiencies, otherwise they operate as an on/off control that fall into the 1% (maybe 0%) efficiency category. This is because some boiler brands prefer to restrict compatibility to their own controls for a multitude of reasons.

Consumers are also uninformed on the true efficiency of smart controls. If they do not speak the same language as the boiler they are little more efficient than a basic on/off control and as an industry we are long past such rudimentary measures.

The Future Homes Standard and meeting net zero by 2050

The Government’s Future Home Standard proposes a significant uplift in the energy efficiency standards for new build homes. By 2025, at the latest, it is proposed that no new homes are connected to the gas grid. An interim uplift in standards will come into force this year. (The proposed standard for existing homes is due out shortly.)

The interim standards make no proposed changes to boiler or system efficiency, only to move from the SEDBUK rating of 89.5% to ErP of 92% in line with standards for existing properties. But as we now know, this does not represent an uplift in efficiency.

Some mention is made of limiting system design temperatures to 55 degrees or lower, which would improve efficiencies, but nothing is stated on how this achieved.

The complete absence of a tightening of heating controls standards under Boiler Plus is an opportunity missed. Tangible efficiency improvements will only come with mandatory requirements to fit compensation controls that offer a 3-4% uplift and ensure universal compatibility.

Energy Performance Certificates (EPC)

Aside from raising questions over the usefulness of boiler efficiency labelling, consumers continue to be deceived by expected energy savings from new boilers. The current EPC guidance recommends that householders with non-condensing boilers should move to a condensing boiler, at a cost of £2,000-£3,000, in order to improve the energy efficiency banding of their homes.

Condensing boilers fitted from 2000 onwards had efficiencies of around 78%. As most new boilers are fitted with an on/off control (including smart controls when they do not speak the same language) then they are at risk of achieving a very small uplift in efficiency and a similarly small reduction in fuel bills.

Where it has gone wrong - misinformation and misguidance in domestic heating

Within many parts of the domestic heating industry it is known that correctly sized boilers, modulating (aka compensation) controls and flow-setting radiator valves can comfortably shave 15-30% off our gas consumption for very little cost. For replacement boilers there is really no extra cost in getting this right.

The bad news is this is not widely understood, implemented, regulated or marketed. The problems behind this are complex, but certainly boiler oversizing, one-size-fits-all boiler manufacturing, insufficient retraining for installers, misinformation for consumers and weak legislation are in the mix.

In 2011, the Carbon Trust reported on field trials that tested the actual efficiencies of 27 condensing, A-rated system boilers. The trials found that “a significant number of them [boilers] were found to be substantially over-sized for the properties in which they were fitted and this is believed to be common practice in the UK”.

Oversizing does not make poorly controlled boilers that much more inefficient, they already are very inefficient, but a correctly sized boiler - with a low minimum output - will work at a much higher efficiency all year round when paired with a weather or load compensation control. In Energy Saving Trust trials, oversized boilers with a basic control gave an average efficiency of 83%. Under the BRE’s ‘SAP heating efficiency of condensing boilers consultation paper’ a lower output boiler with weather compensation control gave an equivalent efficiency of 93.1%.

The report went onto to highlight market failures as a key part of the problem when it stated that “the average peak heat load of UK houses is around 6kW, but the size ratings of new boilers typically range from 10kW to 30kW”.

Most installers would estimate a much higher heat requirement than 6kW because we have all got used to boiler sizes of 18-42kW. These labels often represent the hot water output and this has distorted our understanding of heating requirements, so that consumers often push for bigger boilers, just in case.

Legislation has really done nothing to improve our understanding of efficiency or more importantly ensure that factory rated efficiencies are achieved for condensing boilers. For installers these concepts have been poorly introduced with little training on how best to set up modulating/condensing boilers with weather/load compensation controls.

Putting it right

The good news is, all of this technology is available and affordable and only a little help is needed from Government to get much closer to factory stated efficiencies. We recommend the following changes, that can easily be accommodated within the industry, to bring efficiencies up:

Consumer understanding

It really is labels, labels, labels. Boiler manufacturers can vastly improve consumer understanding if they present information about the boiler and its correct application on the label and in their consumer literature, as follows:

  • Labels need to show that boilers operate within a range of heating outputs, instead of the maximum output, and that the lower the minimum output in the range the more efficiently the boiler can operate all year round when paired with a compensation control.
  • Labels need to give a 'quick-guide' to maximum heat requirements typical properties, e.g. (4-10kW) and guidance that the installer must reduce the maximum output of the boiler to meet it, e.g. 6kW for the average home. This will deal with one-sized-fits-all boilers.
  • Combi boiler labels need to show DHW output in litres per minute (LPM). The current practice of the boiler model referring to DHW output (commonly 24kW- 42kW) distorts consumer understanding of heating requirements.
  • Consumers also need guidance that radiators will not get so hot with compensation controls, but this is not a sign that the boiler is not working.

Regulation tweaks

The Future Homes Standard needs to recognise that boiler efficiencies in the field are much lower that their SEDBUK or ErP ratings and the only way to achieve factory rated efficiencies is to provide much tighter regulation on heating controls. They are readily available and cost no more than on/off smart controls. Minimising design temperatures is a fuzzy standard that will be difficult to police.

The Future Homes Standard must also require that all boilers are compatible with all compensation controls. A universal requirement will make it easier for consumers and for installer training.

Finally the Future Homes Standard must require perfectly balanced systems. So much inefficiency comes from unbalanced radiators. Flow setting (balancing) TRVs are relatively new to the domestic market but have shown efficiency savings of upto 15%. These TRVs prevent the system from overheating and return temperatures rising. They also cost little more than standard TRVs and actually save installers time during commissioning. 

Monitoring and reporting

Actual efficiencies can only be obtained by requiring boiler manufacturers to provide data to consumers on the aggregated efficiency of their heating system. This can be achieved by monitoring how much time the boiler spends in condensing mode and providing a digital reading on the boiler.

It can also provide valuable data to Government, particularly as EPCs calculations are likely to be wildly out and cannot therefore give an indication of true emissions reduction.

Digital monitoring could also be used as an incentive to installers to get the set up correct. For example, extended boiler warranties for consumers are only available for boilers that operate over a benchmark efficiency.

Installer re-training

Assuming the above is implemented, a key roll out of these practices can be via the boiler manufacturers existing training courses, alongside more formal training in these practices. Most run ‘accredited installer schemes’ that inspire loyalty to their brands through training and business support. Part of that accreditation can include training on these concepts.

Future proofing for 2025 and 2050

The success of meeting our 2050 target relies on phasing in low carbon technologies, and rightly so, but we must not overlook firstly, what can be done now to reduce our gas consumption and secondly, that getting system design right will pave the way for low carbon systems.

As the Energy Saving Trust points out, the average UK home needs just 6kW of heat on a very cold day. This is well within the range for fitting an air source heat pump. Systems can be set up now and installers can learn about lower temperature systems now ready for heat pumps.

What we can achieve today is huge. It will reduce our gas emissions in the short term and equip us with the systems and skillsets for a low carbon heating future.

Jo Alsop

Heating Hero

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