Introduction to Boilers
According to the dictionary, a boiler is “an enclosed vessel in which water is heated and circulated, either as hot water or as steam, for heating or power”. Boilers are a mainstay of the UK’s heating infrastructure and according to estimates, there are approximately 1.5 million boilers installed in the UK every year. Heating Central is a key player in the boiler replacement market, with an extensive network of heating and plumbing engineers that specialise in boiler service and replacement.
Boilers have gone through a strong evolution over the last few decades improving their performance, their efficiency, their output and their physical design and looks. New boilers are substantially more efficient, offer better value and are simpler to install and service as part of an efficienct central heating system.
The most important advance has been the introduction of the condensing boiler, which in simple terms recover a substantial percentage of the waste heat that is normally expelled into the atmosphere from the flue of a standard (non-condensing) boiler. By using an extra-large heat exchanger (or two heat exchangers in other cases) within the boiler, the system maximises heat transfer from the burner while recovering useful heat that would normally be lost with the flue gases.
The energy efficiency of a boiler is one of the most important performance parameters of the unit. From 1st April 2005 it has been a requirement of the Building Regulations Part L1 (Conservation of Fuel and Power) that any replacement or new gas fired boiler be of the condensing type unless there are exceptional circumstances.
Types of Boilers
The dramatic increase in efficiency between the traditional and the high efficiency condensing boilers is achieved by further extraction of heat from the gasses that would previously been released through the flue into the outside air. Traditional boilers use a single combustion chamber, enclosed by waterways of the heat exchanger where the hot gases travel. The hot gases then push through the flue (normally at the top most point of the boiler) and go into the outer environment at a high temperature of approximately 180c.
Such reduction in temperature causes the water inside the gases (which are standard outcome of the burning process) to condensate into small drops, and through gravity to roll down to the base of the flue. The rest of the gases are then expelled from the boiler into the outer environment through a fan assisted flue. The water condensate is drained into a discharge pipe or into an external drain.
Plastic and clay drainage are the most effective in dealing with the water which has an acidic properties and contain traces of nitric and sulphurous acids. Cast iron as well as cement and concrete products show the least resilience to this water and will get damaged over time. This problem can also affect older properties with salt glazed drain pipes with cement joints. However in reality the acidic water gets diluted heavily by water from sanitary uses thus reducing the risk of damage to the pipe and drain systems.
Combination Boiler (Combi Boiler)
A similar operations happens upon request for domestic hot water, but rather the valves operate in opposite directions, letting the water pass through to the domestic hot water circuit rather than the central heating system.
Types of Fuels
There are several types of fuels used in the UK for heating and boiler burning. Of the 20 million heating systems estimated to operate throughout the UK, the most common is powered by mains gas boilers, which accounts for about 75% of the market. Oil boilers accounts for about 10% and the remainder is split between solid fuels boilers, electricity and other sources.
Mains gas has grown to become the most popular fuel for domestic boilers. At the moment, new gas mains line are laid every year to keep up with demand. Currently gas mains infrastructure is available to over 85% of UK homes.
Natural Gas 194 g/kWh
Oil is used mainly for heating and domestic hot water heating purposes. Current estimates put number of UK homes that use oil at around 0.9 million.
There are two main types of oil: Kerosene (the most common) and gas oil (mostly used for industrial heating). Both of them are the result of a distillation process of crude oil, with Kerosene being the more refined, lighter and containing less sulphur (which produced the greenhouse gas sulphur dioxide upon burning).
Historically oil was the cheapest fuel, and still has a good network of supply around the UK, with a large number of suppliers covering the country. Supply can be based on requirement and ‘top-up’ is a typical way to keep ones supplies.
LPG is more beneficial than most fuels (except for natural gas) in terms of CO2 emissions. Although it offers many of the advantages of natural gas it suffers from higher cost which makes it less popular.
Natural Gas 194 g/kWh
Historically, solid fuel (wood, coal) was considered to be one of the cheapest fuels available, and even today it still remains competitively priced. Current estimates put the number of UK heating systems using solid fuels boilers at around 4% of the 20 million systems used around the country.
Although it considered ‘dirty’ fuel, there still seems to be strong demand for ‘real fire’, with many seeking to return to more traditional values and are effectively re-opening their fireplaces.
Electric heating is used by about 1.4 million homes in the UK. It is one of the simplest and cheapest heating solutions to install. Yet electricity is the most expensive energy source, even when applying off-peak tariffs.
There are mixed views on the ‘clean’ credentials of electricity heating, as there is no burning of fuels ‘on location’, which grants it green points. However, one should take into account the electricity generation facilities and their respective carbon dioxide emissions during the generation process, the green credentials are less obvious
SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK)
SEDBUK provides the framework for comparison on a fair basis of the energy performance of the various boilers. It was developed under the Government's Energy Efficiency Best Practice Programme with the co-operation of boiler manufacturers
This page has been written with contributions from qualified plumbers from Kent and heating engineers from Ealing. Several of the company's Gas Safe engineers from Middlesex have worked on similar issues as well as some of our plumbers from Bromley and our Notting Hill experienced heating engineers.
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