What year did condensing boilers come out?

Nick Eyre

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Introduction

In 2001 an academic study Socio-technical networks and the sad case of the condensing boiler (Banks 2001), identified the very low uptake of condensing boilers, despite their apparent cost effectiveness. By 2006, almost every gas boiler installed in the UK was condensing. The market was transformed. This note sets out how that change happened.

Early steps

Condensing boilers were developed in the Netherlands in the late 1970s. The technology is significantly, but not radically, different from other boiler technologies. It includes a larger heat exchanger, which cools the flue gas to below the boiling point of water. The water vapour therefore condenses releasing the latent heat of vaporisation and thereby improving the efficiency. The condensate is mildly acidic and needs to be removed through a plastic condensate drain, slightly increasing the complexity of installation.

Early trials established that the technology could deliver significant savings (Trim, 1989). However, by the end of that century, condensing boilers were still not widely deployed with the exception of in the Netherlands (Banks, 2001). With savings of ~10% compared to standard boilers, the potential savings in the UK were the largest for any individual measure in the residential sector. However, as in many other countries, barriers to energy efficiency were constrained adoption. These were already reasonably well-understood, with a typical taxonomy being:

• imperfect information to energy consumers,
• separation of costs and benefits (e.g. the landlord/tenant barrier),
• imperfect capital markets,
• tariff structures which do not reflect marginal costs,
• non-inclusion in prices of externalities, and
• bounded rationality (i.e. deviations from profit/utility maximisation) (Eyre, 1997).

The first step towards policy support was made through an Energy Saving Trust (EST) grant programme which began in 1996. This was funded from the EST’s first annual grant from Defra, established as part of the package to support energy efficiency when the Major government reversed its policy of raising VAT on household from 5% (Mallaburn and Eyre,2014). At the time, the marginal additional cost of a condensing boiler was ~£400 and market share was less than 1%, see Figures 1 and 2. The purchase grant was £200. The market share gradually rose to 3% by 2000, with additional costs falling to about £200.

Figure 1: Condensing boiler installations in the UK 1992 to 2005 (EST, 2008) Image description

Annual installations of condensing boilers grew slowly between 1992 and 2001, with just over 50,000 in 2001. EST grants were introduced in 1995, with support from the EEC in 1999. When the UK regulations were implemented in 2005, over 450,000 installations took place.

Figure 2: Condensing boiler marginal cost 1996 to 2001 (EST, 2008). Incremental costs of condensing boilers dropped from around £450 in 1996, to £167 in 2001.

In a second significant step, support for gas condensing boilers (technically, boilers with a SEDBUK rating of A or B) was a major part of the initial supplier obligation scheme in gas from 2000. (Supplier obligations were introduced later in gas than electricity due to the opposition of the first gas regulator, Claire Spottiswoode.) They were introduced when gas and electricity regulation were combined, and the duties to set supplier obligations moved to Ministers, under the 2000 Utilities Act (Mallaburn and Eyre, 2014). As with all supplier obligations, different companies operated different levels of subsidy at various times, but cashbacks of £200 falling to £100 were probably typical. By 2003, market share was 10% and incremental costs well below £200.

The big step forward – mandatory condensing boilers

Energy efficiency policy was accelerated in the period 2002-2004. The 2002 Energy Review (PIU, 2002) established the principle of energy efficiency being a core part of the energy policy for the first time. This was confirmed in policy in the 2003 Energy White Paper (HMG, 2003), leading to a detailed 2004 Energy Efficiency Action Plan (Defra, 2004)

Condensing boilers were made mandatory from 1st April 2005. The change was made in the 2003 Energy White Paper, announced on 24th March 2003, thereby giving the supply chain 2 years’ notice. The announcement was not widely predicted externally, even by the heating industry. Bearing in mind that the majority of gas fitters had still never installed a single condensing boiler, it was widely considered to be ambitious, raising fears that poor quality installation would blight the policy.

The regulation was implemented through Buildings Regulations, not EU product regulation. Strictly, the legal liability therefore falls on the owner of the building. In practice, compliance with Building Regulations is delivered by the installer acting on behalf of the final customer. Installers were therefore the critical agents. In many cases, these are sole traders or small companies. In turn, they rely on manufacturers and builders’ merchants, who are larger companies with longer planning timescales and the capacity to understand market changes.

The delivery programme

A rapid programme of skills and training was recognised as critically important in the short period between the White Paper publication and implementation of the new standard. This was begun very rapidly and the extent of the programme is described in the 2004 Energy Efficiency Action Plan (Defra, 2004 p76):

“The Energy Saving Trust, in partnership with the Learning and Skills Council; the ‘Skills for Business Network’ comprising four of the Sector Skills Councils; Defra; the heating industry; the Energy Efficiency Partnership for Homes; CORGI; and City and Guilds, is

launching the ‘Energy Efficiency Installer Certificate’. The aim of this initiative is to provide 70,000 installers with the skills needed to specify and install condensing boilers and properly advise consumers on high-efficiency heating systems. Following the completion of pilot courses in 2003, a series of ‘Train the Trainer’ courses were held in February and March of 2004, and the first of the Installer courses commenced in March 2004. We aim to pass 45,000 installers through the programme by 1 April 2005 and a further 20,000 (bringing the total to 65,000) by the end of 2005. The Training programme will be funded from April 2004 until March 2005 by the Learning and Skills Council, though initial funding to get the programme started will be provided by the Energy Saving Trust (with Defra support). The training covers:

• a brief introduction to climate change and the Energy White Paper
• changes to Building Regulations coming in April 2005.
• the elements of high efficiency system specification (boilers, controls etc)

Those successfully completing the training will receive a Level 3 City & Guilds Certificate – ‘The Certificate in Energy Efficiency from Domestic Heating’.”

The programme of training was completed on schedule and was widely recognised as being successful. Indeed, as Figure 1 above shows, the installation rate increased rapidly following the announcement in 2003, with a 30% market share in the year before the regulation was implemented. Faced with a clear regulation, manufacturers changed their product range and supported the necessary training programme. Installers recognised the need to adapt and undertook the necessary training.

The partners involved in the process represented the broad range of interests needed to be “on board” to make the transition work.

• In the lead, a Government funded agency, in this case the Energy Saving Trust – 100% funded through its Defra grant and with the capability and resources to coordinate the programme, delivered through a specialist ‘Trade Programme’ focused on the supply chain.
• Government itself through the (then) lead Department on energy efficiency, Defra – with a strong commitment to implementing the policy it had advocated in the 2003 White Paper.
• The regulator of gas safety, at that time CORGI.
• The equipment manufacturing industry, in this case the boiler manufacturers – facing the reality of a regulatory constraint and therefore motivated to ensure installers of their products could deliver. In practice, much of the training of existing installers was done by major manufacturers, such as Worcester Bosch and Baxi.
• The funders of trade training, then the Learning and Skills Councils.
• The accreditation agency for skills, then, as now City and Guilds.
• A neutral forum convening discussion between the above partners, the Energy Efficiency Partnership for Homes (EEPfH). At that time, the EEPfH had a secretariat provided by EST, although a separate and independent governance structure. Following the ending of the EST core grant, EEPfH was re-founded as a separate stand-alone company, the Energy Efficiency Partnership for Buildings, but closed in 2015. In the period 2003-2005, the EEPfH had many active working groups, including one on heating, which provided the day-to-day forum for discussions on condensing boiler skills and training.

In practice, the majority of these organisations would not have committed to being partners in the absence of the legal commitment in the Energy White Paper.

Impact and conclusions

The transition to condensing boilers is now well-known to have been extremely successful. Savings per boiler, compared to modelled estimates of continuing to use non-condensing boilers, are approximately 2 MWh/year (Elwell et al, 2015). Over the whole boiler stock this saves ~40 TWh/year of gas and emissions of 8 MtCO2/year.

Public policy support was critical in a number of ways, crucially in setting a regulatory framework that provided clarity to a reluctant industry. The critical policy instrument was the decision in 2003 to make installation mandatory in 2005. This was seen as a brave choice at the time.

The use of regulation was enabled by previous policy instruments of grants and supplier obligations. These developed a growing niche market from the late 1990s, allowing the product to be proven and costs to fall. These earlier stages of the transition could have been done quicker if some policies had not been blocked by the gas regulator.

Partnership was critical to delivering the change within the 2-year period between 2003 and 2005. The transition was delivered through a training programme for the boiler installation supply chain. This was a collaborative effort between publicly funded agencies and the boiler industry.

In summary, a combination of regulation, incentives and skills support was needed. This is what would be expected from innovation theory for a change in the dominant regime in a sector (Geels, 2002). It is consistent with wider analyses of the role of multiple policies in delivering energy efficiency (Rosenow et al, 2016).

Implications for future changes to heating

In comparison to other heating system changes, the switch to condensing boilers is relatively easy. There were some early teething problems with freezing of condensate pipes, and consumer acceptance of “pluming”, but these were quickly overcome. Most people were

unaware they had a condensing boiler, because it was a “like for like” replacement for older technology, with no perceptible change in performance. It did not involve whole new skill sets or supply chains in a way that seems inevitable for zero carbon heat.

Some of the conclusions set out above are therefore important lessons for the zero carbon heating transition. A clear regulatory framework will be needed; support for early movers will be important to establish a viable market as soon as possible; and the supply chain will need to be supported to gain the necessary skills.

However, the greater complexity of future changes means that there will be additional issues. The bigger changes in technology appearance, performance and cost raise much more significant issues for consumer acceptance. The changes implied for installers are more profound and therefore will take longer. Perhaps, most significantly, there are major implications for networks (electricity, gas and/or heat), where change will need to be coordinated with change in end-use technology.

References

Banks, N. 2001. Socio-technical networks and the sad case of the condensing boiler. In: Bertoldi, P., Ricci, A., de Almeida, A. (eds) Energy efficiency in household appliances and lighting. Springer, Berlin, Heidelberg.

Defra, 2004. Energy efficiency: The Government’s Plan for Action. CM 6168. London: Crown Copyright.

Elwell, C.A., Biddulph, P., Lowe, R. and Oreszczyn, T. 2015. Determining the impact of regulatory policy on UK gas use using Bayesian analysis on publicly available data. Energy Policy, 86: 770–783. doi: 10.1016/j.enpol.2015.08.020

EST, 2008. Energy Saving Trust. Personal communication.

Eyre, N. 1997. Barriers to energy efficiency more than just market failure. Energy and Environment, 8(1): 25–43. doi: 10.1177/0958305X9700800103

Geels, F.W. 2002. Technological transitions as evolutionary reconfiguration processes: a multi-level perspective and a case-study. Research Policy, 31(8–9): 1257–1274. doi: 10.1016/S0048-7333(02)00062-8

Department for Trade & Industry, 2003. Our energy future – creating a low carbon economy. Energy White Paper. London: Crown Copyright.

Mallaburn, P. and Eyre, N. 2014. Lessons from energy efficiency policy and programmes in the UK from 1973 to 2013. Energy Efficiency, 7(1): 23–41. doi: 10.1007/s12053-013-9197-7

Performance and Innovation Unit, 2002. The Energy Review, pdf. London: Crown Copyright.

Rosenow, J., Fawcett, T., Eyre, N. & Oikonomou, V. 2016. Energy efficiency and the policy mix. Building Research & Information, 44(5-6): 562–574. doi: 10.1080/09613218.2016.1138803

Trim, M.J.B. 1989. Energy in housing: UK monitored case studies indicate opportunity for energy‐saving investment in domestic condensing boilers for family and sheltered housing. Batiment International, Building Research and Practice, 17(2): 108–113. doi: 10.1080/01823328908726950

Publication details

Eyre, N. 2020. The story of condensing boiler market transformation – a briefing note for BEIS. CREDS Policy brief 025. Oxford, UK: Centre for Research into Energy Demand Solutions.

Banner photo credit: Alireza Attari on Unsplash

Type of water heater

Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency (greater than 90% on the higher heating value) by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water. This recovers the latent heat of vaporisation, which would otherwise have been wasted. The condensate is sent to a drain. In many countries, the use of condensing boilers is compulsory or encouraged with financial incentives.

For the condensation process to work properly, the return temperature of the circulating water must be around 55 °C (131 °F) or below, so condensing boilers are often run at lower temperatures, around 70 °C (158 °F) or below, which can require larger pipes and radiators than non condensing boilers. Nevertheless, even partial condensing is more efficient than a traditional non-condensing boiler.

Operational principle

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In a conventional boiler, fuel is burned and the hot gases produced pass through a heat exchanger where much of their heat is transferred to water, thus raising the water's temperature.

One of the hot gases produced in the combustion process is water vapour (steam), which arises from burning the hydrogen content of the fuel. A condensing boiler extracts additional heat from the waste gases by condensing this water vapour to liquid water, thus recovering its latent heat of vaporization. A typical increase of efficiency can be as much as 10-12%.[citation needed] While the effectiveness of the condensing process varies depending on the temperature of the water returning to the boiler, it is always at least as efficient as a non-condensing boiler.

The condensate produced is slightly acidic (3-5 pH), so suitable materials must be used in areas where liquid is present. Aluminium alloys and stainless steel are most commonly used at high temperatures. In low temperature areas, plastics are most cost effective (e.g., uPVC and polypropylene).[1] The production of condensate also requires the installation of a heat exchanger condensate drainage system. In a typical installation, this is the only difference between a condensing and non-condensing boiler.

To economically manufacture a condensing boiler's heat exchanger (and for the appliance to be manageable at installation), the smallest practical size for its output is preferred. This approach has resulted in heat exchangers with high combustion side resistance, often requiring the use of a combustion fan to move the products through narrow passageways. This has also had the benefit of providing the energy for the flue system as the expelled combustion gases are usually below 100 °C (212 °F) and as such, have a density close to air, with little buoyancy. The combustion fan helps to pump exhaust gas to the outside.

Usage

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Condensing boilers are now largely replacing earlier, conventional designs in powering domestic central heating systems in Europe and, to a lesser degree, in North America. The Netherlands was the first country to adopt them broadly.[2]

Efficiency

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Condensing boiler manufacturers claim that up to 98% thermal efficiency can be achieved,[3] compared to 70%-80% with conventional designs (based on the higher heating value of fuels). Typical models offer efficiencies around 90%, which brings most brands of condensing gas boiler in to the highest available categories for energy efficiency.[citation needed] In the UK, this is a SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK)[4] Band A efficiency rating, while in North America they typically receive an Eco Logo and/or Energy Star Certification.

Boiler performance is based on the efficiency of heat transfer and highly dependent on boiler size/output and emitter size/output. System design and installation are critical. Matching the radiation to the Btu/Hr output of the boiler and consideration of the emitter/radiator design temperatures determines the overall efficiency of the space and domestic water heating system.

One reason for an efficiency drop is because the design and/or implementation of the heating system gives return water (heat transfer fluid) temperatures at the boiler of over 55 °C (131 °F), which prevents significant condensation in the heat exchanger.[5] Better education of both installers and owners could be expected to raise efficiency towards the reported laboratory values. Natural Resources Canada[6] also suggests ways to make better use of these boilers, such as combining space and water heating systems. Some boilers (e.g. Potterton) can be switched between two flow temperatures such as 63 °C (145 °F) and 84 °C (183 °F), only the former being "fully condensing." However, boilers are normally installed with higher flow temperature by default because a domestic hot water cylinder is generally heated to 60 °C (140 °F), and this takes too long to achieve with a flow temperature only three degrees higher. Nevertheless, even partial condensing is more efficient than a traditional boiler.

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Most non-condensing boilers could be forced to condense through simple control changes. Doing so would reduce fuel consumption considerably, but would quickly destroy any mild steel or cast-iron components of a conventional high-temperature boiler due to the corrosive nature of the condensate. For this reason, most condensing boiler heat-exchangers are made from stainless steel or aluminum/silicon alloy. External stainless steel economizers can be retrofitted to non-condensing boilers to allow them to achieve condensing efficiencies. Temperature control valves are used to blend hot supply water into the return to avoid thermal shock or condensation inside of the boiler.

The lower the return temperature to the boiler the more likely it will be in condensing mode. If the return temperature is kept below approximately 55 °C (131 °F), the boiler should still be in condensing mode making low temperature applications such as radiant floors and even old cast iron radiators a good match for the technology.

Most manufacturers of new domestic condensing boilers produce a basic "fit all" control system that results in the boiler running in condensing mode only on initial heat-up, after which the efficiency drops off. This approach should still exceed that of older models (see the following three documents published by the Building Research Establishment: Information Papers 10-88 and 19-94; General Information Leaflet 74; Digest 339. See also Application Manual AM3 1989: Condensing Boilers by Chartered Institution of Building Services Engineers). By way of contrast Weather compensation systems are designed to adjust the system based on inside, outside, boiler inlet, and boiler outlet temperatures.

Heat pumps are typically three times more efficient than condensing boilers (based on actual energy input).[7]

Control

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The control of the domestic condensing boiler is crucial to ensuring that it operates in the most economic and fuel efficient way. The burners are usually controlled by an embedded system with built-in logic to control the output of the burner to match the load and give best performance.

Almost all have modulating burners. These allow the power to be reduced to match the demand. Boilers have a turndown ratio which is the ratio of the maximum power output to the minimum power output for which combustion can be maintained. If the control system determines that the demand falls below the minimum power output, then the boiler will cycle off until the water temperature has fallen, and then will reignite and heat the water.

Reliability

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Condensing boilers are claimed to have a reputation for being less reliable and may also suffer if worked on by installers and plumbers who may not understand their operation.[8] Claims of unreliability have been contradicted by research carried out by the UK-based Building Research Establishment (see Building Research Establishment).

In particular, the problem of 'pluming' arose with early installations of condensing boilers, in which a white plume of condensed vapour (as minuscule droplets) becomes visible at the outlet flue. Although unimportant to boiler operation, visible pluming was an aesthetic issue that caused much opposition to condensing boilers.

A more significant issue is the slight (pH 3-4) acidity of the condensate liquid. Where this is in direct contact with the boiler's heat exchanger, particularly for thin aluminium sheet, it may give rise to more rapid corrosion than for traditional non-condensing boilers. Older boilers may also have used thick cast heat exchangers, rather than sheet, which had slower time constants for their response but were also resistant, by their sheer mass, to any corrosion. The acidity of the condensate means that only some materials may be used: stainless steel and aluminium are suitable, mild steel, copper or cast iron are not.[9] Poor design or construction standards may have made the heat exchangers of some early condensing boilers less long-lived.

Initial testing and annual monitoring of the heat transfer fluid in condensing boilers with aluminium or stainless steel heat exchangers is highly recommended. Maintenance of a slightly alkaline (pH 8 to 9) liquid with anti-corrosion and buffering agents reduces corrosion of the aluminium heat exchanger. Some professionals believe that the condensate produced on the combustion side of the heat exchanger may corrode an aluminium heat exchanger and shorten boiler life. Statistical evidence is not yet available since condensing boilers with aluminium heat exchangers have not been in use long enough.[citation needed]

Building Research Establishment

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The Building Research Establishment, which is the UK's major research body for the building industry, produced a leaflet on domestic condensing boilers. According to the Building Research Establishment:

• modern condensing boilers are as reliable as standard boilers
• condensing boilers are no more difficult to service, nor do they require more frequent servicing
• servicing is not expensive; the only (minor) additional task is to check the correct function of the condensate drain
• condensing boilers are not difficult to install
• under all operating conditions, condensing boilers are always more efficient than standard boilers[10]

Exhaust

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The condensate expelled from a condensing boiler is acidic, with a pH between 3 and 4. Condensing boilers require a drainpipe for the condensate produced during operation. This consists of a short length of polymer pipe with a vapour trap to prevent exhaust gases from being expelled into the building. The acidic nature of the condensate may be corrosive to cast iron plumbing, waste pipes and concrete floors but poses no health risk to occupants. A neutralizer, typically consisting of a plastic container filled with marble or limestone aggregate or "chips" (alkaline) can be installed to raise the pH to acceptable levels. If a gravity drain is not available, then a small condensate pump must also be installed to lift it to a proper drain.

The primary and secondary heat exchangers are constructed of materials that will withstand this acidity, typically aluminum or stainless steel. Since the final exhaust from a condensing boiler has a lower temperature than the exhaust from an atmospheric boiler 38 °C (100 °F) vs. 204 °C (400 °F) a mechanical fan is always required to expel it, with the additional benefit of allowing the use of low-temperature exhaust piping (typically PVC in domestic applications) without insulation or conventional chimney requirements. Indeed, the use of conventional masonry chimney, or metal flue is specifically prohibited due to the corrosive nature of the flue products, with the notable exception of specially rated stainless steel and aluminum in certain models. The preferred/common vent material for most condensing boilers available in North America is PVC, followed by ABS and CPVC. Polymer venting allows for the added benefit of flexibility of installation location including sidewall venting saving unnecessary penetrations of the roof.

Cost

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Condensing boilers are up to 50% more expensive to buy and install than conventional types in the UK and the US. However, as of 2006 , at UK prices the extra cost of installing a condensing instead of conventional boiler should be recovered in around 2–5 years through lower fuel use (for verification, see the following three documents published by the Building Research Establishment: Information Papers 10-88 and 19-94; General Information Leaflet 74; Digest 339; see also Case studies in Application Manual AM3 1989: Condensing Boilers by Chartered Institution of Building Services Engineers), and 2–5 years[citation needed] at US prices. Exact figures will depend on the efficiency of the original boiler installation, boiler utilisation patterns, the costs associated with the new boiler installation, and how frequently the system is used. The cost of these boilers is dropping as the mass takeup enforced by government takes effect and the manufacturers withdraw older, less efficient models, but production cost is higher than older types as condensing boilers are more complex.

The increased complexity of condensing boilers is as follows:

• increased size of heat exchanger, or the addition of a second heat exchanger (it is important that the heat exchangers are designed to be resistant to acid attack from the "wet" flue gases)
• The necessity of a fan-assisted flue (as cooler flue gases have less buoyancy). Many non-condensing boilers also have this feature, however
• as the cooler flue gases produce condensate, this needs to be drained, and so the boilers are plumbed into a waste or drain

With respect to modern boilers, there are no other differences between condensing and non-condensing boilers.

Reliability, as well as initial cost and efficiency, affects total cost of ownership. One major independent UK firm of plumbers stated in 2005 that it had made thousands of call-outs to mend condensing boilers, and that the greenhouse gas emissions from its vans were probably greater than the savings made by the shift to eco-conscious boilers.[8] However, the same article points out that the Heating and Hotwater Information Council, together with some installers, have found that modern condensing boilers are just as reliable as standard boilers.

Phase out

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Gallery

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• Condensing boiler

• Condensing boiler exhaust vapour

• Condensing boiler

• Stainless steel exhaust with condensate

See also

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References

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