Modern Central Heating Boilers
If you're looking to replace your existing gas or oil central heating boiler, you should consider buying a Condensing Boiler. Although these typically cost £100-£300 more to buy and install than a conventional modern boiler, they should save this extra cost in as little as 4 years.
What is a Condensing Boiler?
A condensing boiler is a high efficiency modern boiler that incorporates an extra heat exchanger so that the hot exhaust gases lose much of their energy to pre-heat the water in the boiler system. When working at peak efficiency, the water vapour produced in the combustion process condenses back into liquid form releasing the latent heat of vaporisation. A side effect is that this water, known as condensate, which is usually acidic, has to be piped away to a drain or soakaway.
The photo (right) shows a cutaway combination condensing boiler. It is mounted on a wall and the exhaust gases will rise through the plastic flue in the top left corner. Hot water is provided by a small storage tank on the right: the tank (which is covered by insulating foam) has been cut open to show the tightly wound quick refresh coil inside it. At the bottom of the photo are a number of pipes going into the boiler. One carries the gas for the burner and there are two (in and out) for the central heating system. The plastic pipe on the right carries the condensed water vapour produced by burning the gas. This water contains dissolved oxides of sulphur and nitrogen, making it slightly acidic.
Do Condensing Boilers Work?
Ian Byrne, the National Energy Foundation's Deputy Director writes: "YES! Although not many homes in Britain have condensing boilers, over half the new boilers in the Netherlands have been of this type for a number of years. The National Energy Foundation carried out extensive monitoring work on new homes built in Milton Keynes in the late 1980s, and is was found that operating efficiencies of 95% or better could be obtained in normal use. I have had a condensing boiler in my own home for 15 years; it works very well and my heating bills are lower than my neighbours in similar homes with old-fashioned boilers (although most have installed condensing boilers themselves since this page was first written in 1996)."
What size of Boiler do I need?
Most existing boilers are measured by their output in British Thermal Units per hour (Btu/h), but all current boilers are sold in the metric equivalent of kilowatts (kW). The calculator below will give the approximate metric value, but you should bear in mind that in the past central heating engineers often installed boilers that had a higher output than strictly necessary. Although this meant that there was no possibility of the boiler failing to meet the demand for heat, even in the most arctic of conditions, it also meant that they were mainly operating at a part load, and so running below their maximum efficiency. If you have installed additional loft or cavity wall insulation since the last boiler was fitted, it is highly likely that you will need a smaller boiler than before.
We recommend seeking professional advice from a CORGI or OFTEC registered installer before choosing an appropriate replacement boiler.
How can I install a Condensing Boiler? Which model of boiler should I choose?
There are now almost 50 manufacturers or importers with models on the UK market: for a complete list either look on the Government's Standard Efficiency Database for Boilers in the UK website or ring your Energy Efficiency Advice Centre (EEAC) on Freefone 0800-512012. They will also be able to help you on all other aspects of domestic energy efficiency and provide a FREE Home Energy Survey form for you to complete.
EEACs are not able to recommend specific models of boilers, but you should be able to rely on one that carries the Energy Efficiency Recommended kitemark, which is restricted to A and B rated boilers. In fact, the latest edition of the Little Blue Book of Boilers lists over 350 models of "A" rated gas condensing boilers, with an additional 210 models specific to oil or LPG. Even though it is not a legal requirement to install oil condensing boilers until 1st April 2007, with such a wide choice available, there is no reason not to do so.
Where can I find an installer for a condensing boiler?
Most CORGI registered gas engineers in the UK should be able to fit a condensing boiler. Until recently builders were reluctant to install condensing boilers because there were only a limited number of models available and they were rather expensive. Prices have fallen sharply over the past few years, so there are no longer nationally available grants or cashbacks for boilers at present, but EEACs may know of local offers. Some local councils have also grouped together to bulk purchase boilers on behalf of their residents; again local advice centres will know if there is such a scheme operating in your council district.
You may also find a local installer who belongs to the Energy Efficiency Installers scheme. These have been through additional training in energy efficiency, so you can be extra confident of receiving good advice about the best boiler for your home.
What controls do I need with a high efficiency boiler?
Good heating controls require a minimum of four things:
- an electronic timer or programmer that allows separate switching of heating and hot water
- a room thermostat
- thermostatic radiator control valves (TRVs), and
- separate thermostatic control on the hot water system
Additional controls that may be worth considering to get the very best from a central heating system include intelligent heating controls, a weather compensator, a boiler energy manager and full zone control.
Can condensing boilers work with Warm Air systems?
In general, yes, condensing boilers can be used with warm air central heating. These systems were commonly fitted into homes in the late 1960s and 1970s, and many are now in need of a major upgrade or replacement. There are limited number of UK firms specialising in this upgrading work, including Johnson & Starley who maintain a library with the technical specifications of almost all warm air system types ever installed in the UK. New or upgraded warm air systems must comply with the British Standard BS 5864:2004 "Installation and maintenance of gas-fired ducted air heaters", which specifies the selection, installation and maintenance of flued, gas-fired, ducted-air heaters of rated input not exceeding 70 kW (based on net calorific value) used to heat one or more rooms in either domestic or commercial premises. The British Standard is applicable to warm air heaters that incorporate a fan to circulate the warm air. It is also applicable to combined air heater/circulator installations and to the servicing and maintenance of heaters that distribute warm air by natural convection.