How do Condensing Boilers work?

While Condensing Boilers are like normal boilers in many ways, the key difference is in that they try to recover as much waste heat as possible. They do this by reclaiming heat from the waste gases your boiler produces.

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Technical information made simple

All new boilers sold in the UK must be condensing boilers which are rated ‘A’ for efficiency (At least 88% efficiency). They achieve this high efficiency by reclaiming the heat from the hot gases that all boilers produce, which a standard boiler doesn’t do.

Condensing boilers work by using a second heat exchanger to reclaim heat from hot waste gases leaving the boiler, using this heat to heat incoming cold water. This means that the boiler needs to use less fuel to heat that water to the required temperature.

As a result of this heat reclamation process, some of the water vapour in the waste gases condenses into a liquid, which drains away. The gases from the flue of a condensing boiler are typically 50-60°C compared with 120-180°C in a non-condensing boiler, which means that they have a lower propensity to rise.

This means that they need to have a shorter flue. Because of this, condensing boilers need to be situated on an outside wall, preferably on a second floor as the gases will travel less vertically than in a standard boiler. A higher location will also help the condensate drain away – you should try to connect the condensate pipe to another waste water pipe. If you cannot situate your boiler high up, you can use a pump to help the condensate drain away.

Condensing boilers do not always run in ‘condensing mode’ but because they have effective heat exchangers this doesn’t seriously affect the efficiency of the boiler.

Installation

It is important that you use a qualified installer to fit your boiler. Costs can vary considerably, so it’s advisable to get three quotes – our service provides you with three quotes from accredited local installers.

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Find out more about the Installation of Condensing Boilers here.

FAQs

What size should my condensing boiler be?
The type and size of your new boiler will depend on a range of factors like the size of your property, how well it is insulated, and the type of fuel and heating system you use to heat your home. You installer will advise you on the type and size of boiler best suited to your property.
How often should I get my condensing boiler serviced?
It's important to have any gas or oil fired appliance like a condensing boiler serviced once a year. The flue will need checking to make sure it is clear, and a qualified installer should check that your boiler is running safely and efficiently for you. It's best to check with your manufacturer about service schedules, as some boilers may need servicing more than others.
How easy is it to install a condensing boiler?
Boilers vary in size and shape but most are designed for simplicity of installation. With space being such a premium many boilers are small enough to be fitted by one person into a kitchen cupboard, easily and with minimum disruption.
How can a condensing boiler save me money on my energy bills?
Condensing boilers are more efficient than standard boilers and therefore utilise less gas during operation. Modern conventional boilers can only offer a typical efficiency rate of 78%, whereas the rate for condensing boilers is around 88% - i.e. for every £1 spent spent on gas, 88p is converted to actual heat. This adds up to significant savings on annual gas bills, which will enable you to quickly recoup the initial outlay for the boiler and benefit from the extra savings. Complete our Home Energy Survey to find out just how long payback will take in your situation.
How reliable are condensing boilers?
Condensing boilers are reliable if well maintained and serviced regularly. A Which? survey in 2011 found that 46% of owners who bought a boiler after April 2005 have experienced some kind of fault. Not all of these faults required a repair. In fact the most frequent problem, a blocked drainage pipe, experienced by 11% of owners, is actually a problem caused by poor installation.
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