Reaching boiling point
Boilers account for nearly a third of all domestic CO2 emissions. Using a high efficiency condensing boiler could save you money, and significantly cut your home's CO2 emissions.
Jane Turner looks at some of the most efficient gas boilers available.
As from the 1st April 2005 building regulations have required that most
boilers on new or replacement installations in England and Wales are ‘high
efficiency’ which effectively means they will be condensing boilers.
The regulations will apply to Scotland and Northern Ireland from May.
You can buy high efficiency condensing boilers in different types. These
are:
• Combination boilers, which heat up hot water on demand
• System boilers, where a separate hot water cylinder is required
• Heat-only boilers
According to the Energy Saving Trust, if everyone in the UK with gas central
heating installed a high efficiency boiler, we would save enough energy
to heat 3.7 million homes for a year.1 With high efficiency condensing boilers
converting more than 86% of their fuel into heat, compared to an average
of 60% for the conventional types currently in use in the UK,(1) there are
significant financial and CO2 savings to be made by replacing your old boiler.
If it’s 10-15 years old then it probably isn’t energy efficient.
This report looks at natural gas and LPG condensing boilers. All the companies
on the table make both natural gas and LPG models except for Baxi and Potterton
which only make natural gas ones.
What is a high efficiency boiler?
A high efficiency boiler is rated SEDBUK band A or B. Boilers are rated
according to how much of the fuel they consume is converted to heat, as
a percentage. This rating is called SEDBUK - Seasonal Efficiency of Domestic
Boilers in the UK. There is a government-sponsored database (www.sedbuk.com)
for domestic gas and oil boilers both old and new. It enables consumers
and engineers to choose an appliance based upon its efficiency and is the
nearest thing the heating market has to an energy labelling system.(2)
The following diagram shows the bands and their corresponding energy efficiencies.
High efficiency boilers are also known as ‘condensing’ boilers.(2)
A high efficiency condensing boiler works on the principle of recovering
as much as possible of the waste heat which is normally rejected to the
atmosphere from the flue of a conventional (non-condensing) boiler.(1)
This is accomplished by using an extra-large heat exchanger or sometimes
two heat exchangers within the boiler, which maximises heat transfer from
the burner as well as recovering useful heat which would normally be lost
with the flue gases.(1)
Of the 731 natural gas condensing boilers listed on the SEDBUK boiler efficiency
database, 73% were A rated and 23% were B rated. The top rating for a natural
gas condensing boiler is currently 91.5% achieved by two models from Glow-worm:
Ultrapower 100 SXI and Ultrapower 170 SXI (floor mounted combination boiler
24.3 - 24.3 kW). They cost £2000-£2500.
LPG condensing boilers achieve an even higher rating, with a top rating
of 93.3% achieved by the Vaillant Ecomax 613/2E (regular boiler 13.5 - 13.5
kW).
The top rated oil fired boiler achieves a rating of 97.0% but we have not
covered oil boilers in this short report. Oil has a much higher carbon footprint
than gas.
OTHER WAYS OF HOTTING IT UP
Low Carbon Buildings Programme
The DTI’s Low Carbon Buildings Programme (LCBP) will provide grants
for microgeneration and microrenewable technologies to householders, community
organisations, schools, the public and not-for-profit sector and private
businesses. You must undertake a number of energy efficiency measures, such
as loft and cavity wall insulation, before you are eligible to apply for
a LCBP grant. You can currently get grants for solar photovoltaics, wind
turbines, small hydro, solar thermal hot water, ground source heat pumps
and biomass but not yet for micro CHP renewable CHP or fuel cells.(8)
According to a different government department, DEFRA, wood chip boilers
are seen as the most cost-effective microgeneration technology in terms
of energy saving potential, followed by micro CHP heat pumps, micro-hydro
and micro-wind. Solar photovoltaic panels are ranked as the least cost-effective
of all proposed measures.(9)
We have not covered any of the companies making these technologies in this
report for reasons of space. We did however look at solar photovoltaics,
wind turbines and solar thermal hot water companies in issue 95. You can
also see the reports and score tables on this website.
Biomass boilers
Biomass boilers are run on wood pellets, logs or chips. Biomass is called
a carbon neutral technology because the CO2 released when energy is generated
from biomass is balanced by that absorbed during the fuel’s production.(1)
Log boilers must be loaded by hand and may be unsuitable for some situations.
Automatic pellet and wood-chip systems can be more expensive. A typical
20kW (average size required for a three-bedroom semi-detached house) pellet
boiler would cost around £5000 installed, including the cost of the
flue and commissioning. A manual log feed system of the same size would
be slightly cheaper.(1) The maximum LCBP grant is £1500 regardless
of size, subject to an overall 30% limit (exclusive of VAT).(8)
Producing energy from biomass has both environmental and economic advantages.
It is most cost-effective when a local fuel source is used, which results
in local investment and employment. Furthermore, biomass can contribute
to waste management by harnessing energy from products that are often disposed
of at landfill sites.(1)
Biomass boilers are not included on the SEDBUK boiler efficiency database.
Ground source heat pumps
Fridges and air conditioners are two examples of heat pumps. Ground source
heat pumps (GSHP) transfer heat from the ground via buried pipes into a
building to provide space heating and, in some cases, to pre-heat domestic
hot water.(1)
The temperature at about two metres below the surface of the land remains
fairly constant at about 11°C throughout the year. The heat pump extracts
energy from the ground and transfers it to the water in your boiler.(1)
An electric pump is required to achieve this, however for every unit of
energy used by the pump, 3 to 5 units of energy are extracted from the ground.(1)
A typical 8kW system costs £6,400-£9,600 plus the price of connection
to the distribution system.1 The maximum LCBP grant is £1,200 regardless
of size, subject to an overall 30% limit (exclusive of VAT).(8)
Micro CHP
Micro CHP (combined heat and power) are domestic systems which combine a
boiler with an electricity generator. They are currently being trialled
in the UK. About the size of a washing machine, electricity is generated,
and the heat that is given off as a by-product is captured and used.(1)
CHP can increase the overall efficiency of fuel use to more than 75%, compared
with around 40 per cent from conventional electricity generation. Furthermore,
if the CHP is located at the point of consumption, there is very little
loss of energy through transmission and distribution thereby making it even
more efficient and environmentally friendly.(1)
The potential market for small scale CHP technologies is in the domestic
and SME sectors and could displace some of the one million boilers sold
every year in the UK. However, the technology is not yet fully commercially
available off the shelf and few devices have been installed and tested in
the UK.(6)
There are 40 units installed within the Carbon Trust’s field trial.
Of these, 31 are micro CHP units, mostly in homes and 9 are small CHP units
in commercial premises. The Carbon Trust has been developing a methodology
to assess the carbon saving potential of microCHP units versus typical condensing
boilers. The current expectation is that the Carbon Trust will be able to
publish final conclusions from the field trial in Summer 2007.(4)
Some early indications of carbon saving performance are emerging. Very preliminary
results for micro CHP indicate its performance is not as encouraging as
had been hoped at the outset of the trial. About a third of the micro CHP
installations in the trial would appear to reduce emissions and about a
third increase them with the remainder showing no discernable difference.
The performance of small CHP in businesses seems to be much stronger, where
a number of installations appear to offer cost-effective carbon savings.(5)
The longer the operating hours the greater the economic and environmental
benefit delivered by CHP so CHP is currently mostly used where there is
a simultaneous need for electricity and heat over extended operating periods,
typically more than 17 hours a day. Examples of applications include large
chemical plants and paper mills to smaller properties such as hotels, leisure
centres, nursing homes and sheltered accommodation. Therefore, in the UK,
funding for CHP is currently limited to public sector projects.(7)
Links
SEDBUK boiler efficiency database - www.sedbuk.com
The Carbon Trust helps business and the public sector cut carbon
emissions, and supports the development of low carbon technologies - www.carbontrust.co.uk
0800 085 2005
The Energy Saving Trust is a non-profit organisation funded by the
government and the public sector to encourage energy efficiency and the
use of renewable energy sources - www.est.org.uk
0800 512 012
The DTI low carbon buildings programme will provide grants for microgeneration
technologies to householders, community organisations, schools, the public
and not-for-profit sector and private businesses - www.lowcarbonbuildings.org.uk
References
1 Energy Saving Trust website, www.est.org.uk, viewed January 2007
2 Ideal Boilers website, www.idealboilers.com, viewed January 2007
3 Which? September 2006
4 Supprting tomorrow's low carbon technologies — The Carbon Trust (January 2006)
5 The Carbon Trust's Small-Scale CHP field trial update 18th November 2005
6 Small Scale CHP Pilot Field Trials — The Carbon Trust website
7 Baxi Technologies website (www.baxitech.co.uk) viewed January 2007
8 Low Carbon Buildings Programme website (www.lowcarbonbuildings.org.uk ) viewed January 2007
9 ENDS Report, October 2006