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Central Heating
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| What is Central Heating? |
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| Central Heating means heating from a central source. Most modern central heating systems use water as the medium to get heat from the central source (boiler) to all the areas to be heated. |
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| There is no such thing as a standard central heating system, you can tailor the system to suit your needs and with advanced controls the central heating system will be able to constantly monitor and adjust your central heating (without you having to do anything). However even a basic Central Heating system when programmed should look after itself with regards to turning itself on & off automatically, and should use no more fuel than necessary for your needs. Central heating systems when optimized and programmed correctly or additionally with advanced controls, should keep your house at the correct temperature. It should also provide all the hot water you need, when you need it. All this will be achieved whilst burning the minimum amount of fuel. |
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| A centrally heated house will normally be cheaper to run than any other form of heating. For instance independent fires, even just one fire can be more expensive to run than a well designed central heating system with good quality controls. |
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| Central Heating Advice: |
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| Gas central heating is currently the most widely-used method of heating the home. |
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| Before deciding to go ahead and have a boiler/system fitted or replaced it may be advisable to find out what type of central heating system you have. |
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Condensing Boilers
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| Condensing boilers are highly efficient boilers that have much lower fuel and running costs than conventional boilers.Take up has been slow ever since they were first introduced in the early 1980s due to a number of misconceptions and a general lack of awareness. Since then the technology has improved and there has been an increase in the number of trained installers. |
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| In dispelling the misconceptions or ‘myths’ associated with condensing boilers, it is hoped that the barriers to specifying and installing condensing boilers will be finally removed.This will result in a sustained increase in market share throughout the UK, benefiting householders and the environment alike. |
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| Benefits of Condensing Boilers: |
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| Condensing boilers offer tangible benefits by: |
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- Reducing carbon dioxide emissions and helping to combat global warming
- Improving household efficiency thus reducing fuel bills. Condensing boilers work 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
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| 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. When in condensing mode (for condensing boilers do not condense all the time) the flue gases give up their ‘latent heat’ which is then recovered by the heat exchanger within the boiler. |
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| As a result the temperature of the gases exiting the flue of a condensing boiler is typically 50-60°C compared with 120-180°C in a current non-condensing boiler.At the same time an amount of water or ‘condensate’ is produced. |
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| A condensing boiler will always have a better operating efficiency than a conventional non-condensing one, due to its larger and more efficient heat exchanger.The benefits of condensing boilers are therefore quite clear, and in order to encourage greater takeup of these benefits we now need to address the myths surrounding them. |
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| The Myths Surrounding Condensing Boilers: |
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Myth: They are only efficient when fully condensing
Response: Not true. Due to its larger heat exchanger, a condensing boiler does not have to condense in order to be more efficient.Typically a new gas condensing boiler will have a seasonal efficiency of between 84% and 92% compared with a new non-condensing boiler at 78% or an older boiler at 55-65%. See table below for typical annual fuel costs for condensing and non-condensing boilers. |
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| The SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) rating is the average annual efficiency achieved in typical domestic conditions and is quoted in a series of bands (from ‘A’ at 90% or over, to ‘G’ at below 70%).The SEDBUK is linked to current Building Regulations in England,Wales[1] and Scotland[2], but not Northern Ireland[3] and some boilers which are rated A-B are endorsed as ‘Energy Efficiency Recommended’. |
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Myth: They are too expensive
Response: In the past, condensing boilers were more expensive,
mainly due to the materials used in the construction of the heat exchanger. However, as with all new things, the cost of technology reduces over time, and some regular condensing boilers can now be obtained for no more than a regular non-condensing boiler. |
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Myth: They need larger radiators
Response: No change necessary. In most systems, radiators are already oversized for all but the severest weather. A marginal benefit of approximately 3% may be obtained from oversizing radiators for a new system, as this will allow slightly cooler return water to the boiler and maximise time spent in condensing mode, but this is usually uneconomic and impractical. |
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Myth: They are less reliable
Response: Not true.This was true with the early models of condensing boilers, but through improvements introduced as a result of this early experience, the components in modern condensing boilers are as reliable as those in the equivalent non-condensing models. |
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Myth: They are difficult to install
Response: Not true.The only difference compared with noncondensing boilers is the requirement for a condensate drain. |
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| A competent installer will have no problem in deciding on a suitable location for the drain and fitting a normal, plastic overflow pipe. Flue locations will also need consideration – see myth on ‘pluming’. |
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Myth: They are harder to maintain
Response: Not true.The only minor difference is the need to ensure that the condensate drain is clear when servicing. |
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Myth: They cannot be fitted to existing systems
Response: Not true. Condensing boilers are suitable for replacing most existing boilers.As with any replacement boiler, the effectiveness of the control system and type of hot water cylinder should be assessed when conducting a site survey.
Consideration should also be given to cleaning and flushing the system before fitting a new boiler. |
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| Wall hung condensing boilers are readily available, with extended fluing options if required. |
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Myth: They have limited availability
Response: Not true.The number of manufacturers offering both regular and combination condensing boilers is increasing all the time, with major players offering dozens of different models. |
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Myth: The plume is a nuisance
Response: Because the flue gases leaving a condensing boiler are cool, they tend to produce a noticeable mist or plume of water vapour around the flue terminal itself (as they condense upon contact with the atmosphere), especially under cold conditions.This is not a problem and in fact indicates that the boiler is working as intended. However, consideration should be given to boiler and flue location prior to installation so that the plume will not be too close to neighbouring properties or windows, doors and paths regularly used in the winter. |
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Myth: The condensate is a problem
Response: Not true.With modern systems, only about one litre per hour of condensate is produced, which has a pH in the range of 3.5 to 5 – about the same acidity as tomato juice. As previously discussed, this is carried to a normal drain by means of a simple plastic overflow pipe. |
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Combination Boilers
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| A ‘Combi’ boiler is called this because it heats your house and heats water for your taps on demand. This means that when you run the hot tap your boiler fires up and heats that water that will help you wash up or clean your hands. |
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| At the same time it could be heating your home’s radiators so doing 2 things in ‘combi’nation. |
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| The benefits are: |
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- Cheaper to install
- Can be cheaper to run as there is no hot water store to heat
- Hot water when you want it
- New rules introduced in 2005 say that all new boilers have to be Condensing Boilers. This is sometimes misunderstood as meaning they have to be ‘Combi’
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| This is not true. Your boiler can either be ‘Combi’ or have a Hot water cylinder to heat water. The important thing is that the boiler is Condensing. |
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Fully pumped Systems
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| The term for any boiler that uses a pump to move all the heat from the boiler to every part of the system is "Fully Pumped". As a rule, one pump is used to circulate the water through the valves which divert the flow to the relevant part of the system. A fully pumped system, in conjunction the appropriate peripheral controls, can provide the user with a lot of control over how the heat is distributed, as well as at what time and temperature the heat is supplied. |
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| With all fully pumped systems that incorporate a remote hot water cylinder, you can have an electric Immersion Heater as a backup for the hot water in case of a fault occurring in the gas central heating system. |
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Sealed Systems
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| Central heating systems currently being installed in the UK are increasingly of the sealed primary circuit type. This means the water heated by the boiler, which circulates around the radiators is held in a closed circuit under pressure. Such an arrangement has a number of advantages over ‘open-, vented’ or ‘conventional’ heating systems. Sealed systems are low maintenance, but are not maintenance free. Combination boilers invariably have sealed circuits. |
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| Some of the advantages of sealed systems are: |
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- They are simpler to install since there is no header tank in the roof space, and consequently none of the associated problems (i.e. overflowing or freezing).
- They are easy to fill since air is expelled under pressure when bleeding the radiators
- As the system is sealed, the problem of air being drawn into the system through open vents is eliminated, therefore the likelihood of airlocks, corrosion and sludge build up is significantly reduced
- Increased pressure raises the boiling point of the water within the boiler, promoting quieter operation
- There is a fixed volume of water within the system (i.e. the system will not replenish any losses automatically), so in the unfortunate event of a leak the escaping water is limited
- They save space in locations such as flats, where there are usually no convenient locations for the header tank
- The system can be flushed out under pressure using the mains water supply
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Wall boilers
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| The above systems can be used with any type of boiler although the most popular is a wall boiler. |
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| As the name suggests this type of boiler is wall mounted and can either a "combi" or a regular heat only boiler. The main advantage of this boiler is flexibility of location and amount of space taken up by the appliance. |
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Floor Boilers
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| As above a floor boiler will provide the neccesary requirements for all central heating applications though due the size and location issues they tend not to be very popular although in combi form they tend to provide a better hot water flow rate. |
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Back Boilers (BBUs)
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| This type of boiler is situated behind a gas fire (the fire and boiler are sold as one unit) usually in the lounge. These systems are fairly outdated and very inefficient and therefore should only be considered as a replacement of an existing back boiler unit. |
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Flues
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| The flue on a gas appliance takes the products of combustion from the appliance to the outside air. An open flued appliance takes the air required from within the room the appliance is located and requires a purpose provided air vent depending on the amount of gas the appliance burns |
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| The only gas appliances still for sale with an open flue are gas fires or back boiler units. Most modern applinces have a room sealed fan assisted flue.This has the advantages of taking air directly from outside and therefore requires no purpose provided ventilation and also greatly reduces the risk of carbon monoxide poisoning. |
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| As they products of combustion are expelled with the assistance of a fan there is also much greater flexibilty with siting the appliance. |
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Efficiency
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| Boilers account for around 60% of the carbon dioxide emissions in a gas heated home. By fitting a new high efficiency condensing boiler and improving your heating controls, you will significantly cut your home’s carbon dioxide emissions and could save as much as £275 a year. |
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| As the current lifespan of a boiler is around 15 years, choosing a heating system with a high efficiency condensing boiler with the correct heating controls can make a huge difference to your heating bills over time. |
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| A high efficiency condensing boiler works on the principle of recovering as much as possible of the waste heat which is normally wasted from the flue of a conventional (non-condensing) boiler. The best high efficiency condensing boilers convert more than 90% of their fuel into heat, compared to 78% for the best conventional types. |
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| If you’re shopping for a new boiler always look for the Energy Saving Recommended logo. It’s your guarantee that these products have met the strict criteria on energy efficiency, will cost less to run and help reduce carbon emissions. |
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Unvented System
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| The traditional British domestic hot water supply system, in which water is heated and stored for use, is based on cold water feed from a storage cistern to a heated cylinder that is vented to the atmosphere. The flow rate and pressure of the hot water discharged from the hot water outlets is then dependent on the height of the storage cistern above the outlets. |
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| However increasing demand to remove cisterns from the roof space means greater difficulties in meeting consumer demands for high performance hot water systems, from traditional open vented systems. This is particularly the case with the growing market for high performance showers. |
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| Unvented domestic hot water systems can, however, meet these expectations by utilising cold water supplied directly from the mains to the heated storage cylinder. Included with the cylinder is a package of safety devices and controls to regulate temperature and pressures within the system. This type of system can provide flow rates in excess of 25 litres/min thus meeting BS6700 specification for design flow rates of 18 litres/min whilst retaining the facility for simultaneous draw-off from other hot water outlets. |
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| Means of Water Heating: |
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| The means of heating the water in the storage cylinder may be either a) direct, which entails one or more immersion heaters in the cylinder, or b) indirect, in which case the contents of the storage cylinder are heated by a primary heater of the coil heat exchanger type. |
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| In both cases the heat source is subject to thermostatic control. Should the thermostat fail the energy input to the storage cylinder, either from an immersion heater or a coil heat exchanger, will be interrupted by an energy cut-out |
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| Advantages of the Unvented System: |
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| The advantages of the unvented system are: |
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- Balanced hot and cold water pressures.
- Improved shower performance.
- Less pipework and no storage cistern.
- Reduced risk of frost damage to system.
- Saving on installation time and costs.
- Excellent heat transfer capability.
- Allows the use of a wider range of modern tap fittings and showers.
- Flexibility of vessel siting and hence system design
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