The high efficiency boiler has been marked as one of the most important advances in boiler technology, allowing both energy savings in the form of CO2 emissions and economic benefits in terms of reduced heating bills. High efficient boilers may also reduce the amount of gases such as NOx, and SOx that are released into the environment [3].
What is a high efficiency condensing boiler?
The main difference between a condensing and non-condensing boiler is that a condensing boiler actually uses the latent heat, which is released from the burning fuel, converting it from vapour into water [1]. In traditional boilers there is a single combination chamber, which is surrounded by waterways of the heat exchanger where the hot gases travel. At the top of the boiler there is the flue, where the gases push through and escape into the environment at temperatures of around 180c [2]. A condensing boiler will recover a large amount of the waste heat by extracting heat from the exhaust gases. This is known as the ‘condensing mode’ [1, 2]. A high efficiency boiler has an extra-large heat exchanger or two heat exchangers, which allows it to maximise the heat transfer from the burner [2]. This extra-large heat exchanger acts to capture the rising gases which can then be used for domestic use. The gases that do leave the boiler will do so at a much lower temperature of around 55c [2].
The diagram below illustrates how a high efficiency condensing boiler operates. It shows the 2 heat exchangers, which make it possible to recover a higher percentage of the waste heat compared to a conventional boiler [5].
[5]
Two main types of condensing boilers exist: System and Combination boilers. The difference is that System condensing boilers have an internal hot water cylinder that stores the water to heat. Combination boilers do not need this cylinder and provide instant hot water [1].
The Baxi Megalfow System 18 HE LPG. It is band A rated and runs on LPG fuel with an energy output of 18kW. For more information on all band A rated boilers, running on gas, oil and LPG, visit the Energy Saving Trust website [1].
When is it most effective to replace your boiler with a high efficiency-condensing boiler?
Boilers are rated in alphabetical categories from A to G according to their ability (efficiency) to convert fuel to heat as a percentage [1]. In the UK the rating system is called SEDBUK – Seasonal Efficiency of Domestic Boilers in the UK.
A rated boilers are more than 90% efficient and only these have the Energy Saving Trust Recommended logo [1].
Figure 3 illustrates the different ratings and the amount of energy that will be saved if you replace your old boiler with an A rated boiler.
| Old Boiler Rating | Annual Saving (£/yr) | Annual Saving (kgCO2/yr) |
| G (< 70%) | £235 | 1,100 |
| F (70% – 74%) | £105 | 700 |
| E (74% – 78%) | £65 | 500 |
| D (78% – 82%) | £55 | 300 |
It is evident from the above table that G rated boilers are the least efficient and the most savings, economic and environmental, can be gained by replacing your G rated boiler with an A rated efficient boiler. If your boiler is more than 15 years old, it is likely to be a G rated boiler. If you have installed a new boiler more recently, it is likely to be more efficient than a G rated boiler, so less overall savings can be made [1].
It is important to check with your boiler installer that your home is compatible for the type of boiler you would like. Combination boilers are usually compatible for most homes but it is not always the case. When installing a new boiler, the Energy Saving Trust advises that you use an installer who is registered with a Competent Person Scheme. These are schemes that allow both individuals and businesses to self-certify their work as compliant with UK Building Regulations [1]. The website, www.competentperson.co.uk allows you to enter your postcode to find the nearest installer.
The Energy Saving Trust has a database containing a range of boilers that will enable you to find the one that is right for you [1]. You can also compare the efficiency of different boilers at www.boilers.org.uk. The SEDBUK website provides information on condensing boilers, efficiency bands and also the government’s boiler scrappage scheme [4].
And finally….
The energy to heat approximately 1.9 million homes for a year and 6.7 million tonnes of C02 could be saved if everyone in the UK, who has gas or oil central heating, replaced their systems with a high efficiency condensing boiler! [1].
References
[1] Energy Saving Trust (2010) [Online] Available from: http://www.energysavingtrust.org.uk/Home-improvements-and-products/Heating-and-hot-water/What-is-a-high-efficiency-condensing-boiler
[2] Heating Central (2010) [Online] Available from: http://www.heatingcentral.com/boilers/plumbers/high-efficiency-boiler-tips
[3] The Carbon Trust (2010) [Online] Available from: http://www.carbontrust.co.uk/cut-carbon-reduce-costs/products-services/technology-advice/Pages/boiler-heat-distribution-replace.aspx
[4] SEDBUK (2010)[Online] Available from: http://www.sedbuk.com.
[5] Pure Energy Solutions (2010) [Online] Available from: http://www.pureenergysolutions.co.uk/page.php?14
