Green Building, Part 3: Electricity and energy efficient boilers

As we have become more aware of the serious impact of human behaviour on the environment, we have also got better at developing new technologies that ameliorate some of the harm we do through pollution and wastefulness with resources. But it’s not just about developing new technologies, but building more eco-friendly systems into older technologies such as boilers. In the following section discover how your choice of boiler can make a positive difference both to the environment and to your pocket. 

Energy Efficient Boilers

The Energy Saving Trust estimate that 55% of our energy bill each year is contributed by our boiler, so an efficient boiler is going to make a serious difference.

The technology of the condensing boiler has come a long way, since the 1980s making it the most fuel-efficient type of gas or oil central heating boiler available with claims of 92%-95% fuel efficiency. It’s been estimated that they are 25% more efficient than non-condensing boilers.

Since April 2005 all new boiler installations must have a SEDBUK (Seasonal Efficiency of Domestic Gas Boilers) rating of A or B – the rating measures the annual average energy efficiency.  Currently only condensing boilers meet this criterion.

With a conventional boiler some of the heat escapes via the flue in the burned exhaust gases. Burning gas creates water vapour which is slightly acidic. In a conventional boiler the heat exchanger is made intentionally small to ensure that all the water vapour produced is carried away and not left to cool, condense and cause corrosion within the boiler.

The condensing boiler is designed to extract the maximum amount of heat from the usable energy. This includes unused heat from the escaping flue gases. Once the heat is removed, the cooled flue gases condense. So unlike the conventional boiler, the condensing boiler has an extra large heat exchanger made of a robust non-corrosive material such as super alloy stainless steel or aluminium. A 40-mm plastic pipe is required to drain the condensed liquid as it drips down the heat exchanger within the boiler. The condensate can be directed to the most convenient kitchen waste pipe or outside drain. Approximately one litre of condensed water vapour is produced per hour. The length of plastic flue and air intake pipes can be run up to ten metres away from the boiler, either vertically or horizontally so siting the boiler is flexible and is not restricted to being placed on an outside wall. However, care should be taken in the positioning of the flue outlet. It should not be too close to a door or opening window because of the plume of gases that could blow back and cause a nuisance and never discharge your flue on to a neighbour’s property.

Condensing boilers are suitable for most sized households. They are energy saving and keep atmospheric polluting emissions to a minimum. The nitrogen dioxide (Nox) emissions of the average conventional boiler are around 150 ppm (parts per million) compared with a low Nox condensing boiler which emits around 5 ppm.

There is no simple formula for calculating the size of boiler or size of radiators you may require, your heating installer should be able to make the calculations for you. This will not only take into account the number and size of rooms that you have, but also will calculate the heat loss through walls, doors and windows by measuring how  well your home is insulated.

There may be situations, such as in the case of a small well-insulated flat where the energy savings made by installing a condensing boiler would be so small that it may not be a requirement. You should talk this over with your local building control officer contactable through you local council.


The good news is that in 2014 greenhouse gas emissions dropped by 8.4 % and Carbon Dioxide output fell nearly a tenth. It’s due to a number of factors: the growth of renewable energy, nearly a fifth of all electricity produced is now renewable; higher temperatures in the UK in 2014. However much can be done in individual houses.

Carbon Dioxide (CO2) is emitted every time a light is turned on.  Significant reductions in these emissions can be made by using energy efficient light-bulbs. Energy efficient light bulbs use up to 70% less electricity than standard tungsten bulbs. Traditional lamps use 90% of their energy emitting heat which is indicative of how energy inefficient they are. Energy efficient lamps are more expensive than their less efficient contemporaries; however, they can last up to 13 times longer with a typical lifespan of 10,000 hours.

Light pipes offer opportunities for energy saving by enabling natural daylight to be brought into rooms that would otherwise have to be illuminated by artificial light.

Also see:

Part 1: Materials

Part 2: Conserving Energy

Part 4: Renewables