Why Are Condensing Boilers More Energy Efficient?

Condensing boilers are modern water heaters, which are widely recommended for their superior energy efficiency levels. Since April 2005, all newly-fitted gas boilers in the United Kingdom are legally required to be condensing boilers, due to their low carbon emissions. Typically, they achieve a higher heating value (HHV) of 90% or more.

According to research, around 55% of an average household’s energy bills are spent on boilers, so ensuring your boiler is as energy efficient as possible is certainly worthwhile for financial reasons. In addition, installing a condensing boiler will reduce your carbon emissions, which will benefit the environment.

This blog post intends to explain how condensing boilers work, the BASIc science behind their superior energy efficiency levels and the positive impact they can have on your household bills.

Condensing Boiler Diagram
Image Author: N Davison
Image License: Creative Commons

How Do Condensing Boilers Work?
A standard boiler heats water by burning natural gas. As a result of this process, both carbon dioxide and water vapour are produced as by-products. These gases then escape through the flue and enter the outside atmosphere, taking with them some of the heat produced by the boiler. In most cases, a standard gas boiler will lose between 20 and 30% of its energy through these escaped gases, giving them an efficiency rating somewhere between 70 and 80%.

Condensing boilers achieve greater efficiency by recovering some of the heat that would usually escape with the waste gas. In order to achieve this, the waste gases are sent through a heat exchanger, which then cools and condenses them back into liquid form. The small amount of gas which does escape is also cooler than it would be with a regular boiler.

The liquid created by the heat exchanger is called condensate and contains much of the heat which would have been lost. This extra heat is then used to pre-heat the cool water that returns to the boiler later. Generally, condensing boilers will only lose around 10% of their energy and a good condensing boiler will have a HHV of more than 90%.

Contrary to popular belief, condensing boilers are just as reliable as conventional boilers and are neither more difficult to service or in need of more frequent service. Installation is relatively simple and the key bonus is that they are always more energy efficient than a standard boiler, no matter what the operating conditions.

Influence on Cost
One aspect which often puts people off upgrading their boiler is the initial cost of installing a new one. However, while it is true that upgrading a conventional boiler to a more modern, condensing boiler could cost somewhere in excess of £2,000, this outlay is offset by the significant savings that will be made as a result of the upgrade.

Indeed, according to figures presented by the Energy Saving Trust, upgrading an old boiler, with an energy efficiency rating of 70-74%, to a newer condensing boiler, with an energy efficiency rating of 90%, would lead to annual savings of over £200 for a three bedroom, gas-heated house. That amounts to a carbon saving of more than 800kg every year. If the old boiler has an energy efficiency rating of less than 70%, annual savings could top £300.

Moreover, there are currently several government schemes in operation, which offer free upgrades, in an effort to reduce the country’s total carbon emissions. People receiving certain benefits, including Job Seeker’s Allowance and Income Support, as well as those with an old, G-rated boiler, may be eligible for this free upgrade, completely eliminating the initial cost. To find out if your household qualifies, contact BASI Heating today

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