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What is a Condensing Boiler?


The UK winter is cold, both in the literal and metaphorical sense. In a bid to keep your family warm and comfortable during this period, you have to invest in a highly efficient boiler that will fulfil your home’s heating needs while consuming the least possible fuel. And, even if you are relatively green in the field of boilers, you must have heard the term “condensing boiler” and are probably wondering if it would fit the role.

If you are currently in this predicament, you can take a breather as you have come to the right page. In this guide, we will explain everything there is to know about condensing boilers, including what they are, how they work, and their potential benefits. So buckle up as we dive to uncover the story of condensing boilers.

What is a condensing boiler?

A condensing boiler is a highly efficient and eco-friendly boiler that re-uses some of the waste gases produced from gas or oil fuel combustion to heat the returning water in your boiler system. By recycling this waste heat, the condensing boiler achieves energy efficiencies greater than 90%, saves money, and reduces carbon emissions.

The condensing boiler’s high energy efficiency and low fuel usage can help you save between £200 and £300 on your annual energy bill. On the other hand, its eco-friendliness and low carbon emissions could lower your yearly carbon dioxide production by a significant margin.

These features, coupled with the government requirement that all new boiler installations in the UK be condensing, have helped make the condensing boiler the most predominant boiler type in the UK.

How much does a condensing boiler cost?

The cost of installing a condensing boiler on your property will vary depending on the boiler’s brand, size, and model. It will also greatly depend on the complexity of the installation project and whether you’ll be adding extra attachments such as intelligent controls and filters.

You will typically have to forge out between £500 and £2,500 to acquire a stand-alone condensing boiler. When installation costs are factored in, the total cost could potentially rise to anywhere between £1,500 and £3,500.

How to select the best condensing boiler for your home

When shopping for a new or replacement condensing boiler, you need to pay attention to the boiler’s output rating as it helps determine its suitability for your home. You also need to be attentive to its efficiency rating displayed as ErP and the warranty contract as they are instrumental in making an informed decision.

How does a condensing boiler work?

As the name suggests, a condensing boiler uses condensing technology to ensure better use of the energy it generates through the combustion of gas or oil fuel. When these fuels are burned, the heat generated is transferred from the burner to the primary heat exchanger, where it is held for quite some time. Trapping the hot gases at the primary heat exchanger allows them to heat the water in the boiler system effectively.

After exiting the primary heat exchanger, the hot combustion gases, now at a temperature of around 200°C, are taken to the secondary heat exchanger. At the secondary heat exchanger, heat is extracted from the waste gases and used to heat the returning water in the radiator or the domestic hot water system.

With the heat extraction, the temperature of the waste gases drops to around 55°C. The gases are then allowed to exit the boiler via the flue. The drop in the temperature of the waste gases also causes the water vapour to condense, forming water droplets that are then drained via the external condensate pipe.

The recycling of the waste combustion gases in a condensing boiler ensures minimal heat loss. This, in turn, leads to better heat efficiency, lower fuel consumption, and an overall decrease in heating costs.

What is the difference between a condensing boiler and a non-condensing boiler?

Several features distinguish the condensing boiler from its predecessor, the non-condensing boiler, otherwise known as the open vent boiler. First, a condensing boiler is fully sealed and takes air from outside the building, whereas the non-condensing boiler typically takes air from inside the room.

Secondly, the condensing boiler can recycle some of the produced heat, resulting in high energy efficiency, whereas the non-condensing boiler doesn’t have this capability, hence its low energy efficiency. Efficiency-wise, the condensing boiler can unlock efficiencies of up to 98%, whereas the non-condensing boiler can only achieve a rating between 70-80%.

Lastly, the condensing boiler has two heat exchangers, whereas the non-condensing boiler has a single heat exchanger.

Typically speaking, all boilers installed before 2005 are predominantly non-condensing, whereas those installed after April 2005 are mainly condensing.

Is a condensing boiler the same as a combi boiler?

Although you might have heard the term “combi boiler” being used interchangeably with “condensing boiler”, they are two entirely different terms. A combi boiler refers to a single heating unit that can provide heating and hot water on demand. In contrast, a condensing boiler refers to a boiler unit capable of recycling waste combustion gases.

The confusion between the two arises primarily due to the increasing popularity of combi boilers across UK households and the fact that all combi boilers produced from 2015 onwards are condensing. However, it is essential to note that although all the combis you come across can be condensing, all condensing boilers don’t necessarily have to be combi boilers.

How do I know if my boiler is condensing?

If you have recently switched properties, it is normal to be unsure whether the boiler supplying heating and hot water to your new home is a condensing boiler or not. However, there is no need to panic as you can simply determine the nature of the boiler by checking out the following things:

  • The boiler manual: The first thing you need to check is your boiler’s manual, as it clearly states whether the boiler is a condensing or a non-condensing one.
  • The installation date: If the boiler was installed after April 2005, it is a condensing boiler as all UK boilers manufactured after this period are condensing.
  • Presence and nature of the flue: If your condensing boiler has a metal flue coming out of your home’s exterior wall or roof, then it is most likely to be a condensing boiler.
  • Steam and drainpipe: A condensing boiler will have steam coming out of the flue and a white plastic pipe that leads to a drain.

Types of condensing boilers

Given that all new boiler installations have to be condensing boilers, it suffices to say any recently installed boiler is a condensing boiler. However, the type of condensing boiler installed on your property will depend on your personal preference and its suitability to your home’s heating needs. That said, the common types of condensing boilers are:

  • The combi boiler: They are the recent addition to condensing technology and quickly gaining approval. Combi boilers entail a single unit that delivers heat and hot water on demand without external tanks. The cost-effective trait of the combi boiler is what appeals to most homeowners.
  • System boilers: These boilers draw their water from a water tank in the loft area of the property rather than from the mains. They also store the heated water in a hot water cylinder, ready for delivery at any time. These systems can directly meet domestic hot water demands from their hot water cylinder.
  • Regular boilers: They are more traditional boilers, mainly with older properties. Despite this fact, some regular boilers are condensing boilers as well.

Benefits of a condensing boiler

Thanks to its many potential benefits, the condensing boiler has managed to garner legislation support from various governments across Europe. Some of these benefits include:

  • Cost-effective

The condensing boiler is 15-30% more efficient than a non-condensing boiler giving it a clear edge over its conventional counterpart. With an efficiency rating higher than 90%, the condensing boiler will cut down your fuel usage and significantly lower your annual energy bills.

  • Reduces the carbon footprint

The condensing boiler is one of the most environmentally-friendly heating solutions out there, thanks to its large heat exchanger and ability to recycle waste gases back into the system. As a result, they emit fewer carbon emissions than traditional non-condensing boilers. In fact, your condensing boiler can help cut your carbon emissions by an impressive 1700 kg each year. It is, therefore, unsurprising that many governments across the globe are mandating all new boiler installations to be condensed.

  • Space-saving

Condensing boilers do not require additional ventilation or a hot water tank that takes up space. They are sleek and compact in design, allowing them to take up the least possible space in your home. Some more compact models of condensing boilers can even be tucked away inside a standard kitchen cupboard, freeing up much-needed space in your home.

  • Wireless programming

Modern times are exciting, and the condensing boiler lets you experience just that. It is compatible with smart thermostats and allows you to control and alter the air temperature in your home remotely.

  • Safety

Condensing boilers are sealed systems that take air for combustion from outside your home rather than inside the room. This means that there is a lower risk of things being sucked into the boiler and causing it to break down.

What are the disadvantages of condensing boilers?

Like any other type of boiler, condensing boilers have shortcomings that you need to consider when deciding to ditch your non-condensing boiler for it. Some of these disadvantages include:

  • It requires extra plumping

Before making the switch, you will have to install a flue and a drain or condensate pipe, meaning you have to invest in additional plumping.

  • It is costly to repair and maintain

Because condensing boilers have a lot of pipework and plumping, it would be complex and expensive to fix if it breaks down.

  • It produces toxic wastes.

The acidic condensate from the boiler is highly corrosive and can eat away the condensate pipe, resulting in extra repair costs. Moreover, the condensate is toxic and needs to be disposed of appropriately.

What are the common condensing boiler problems?

The condensing boiler can experience issues common to other boilers, but a frozen or blocked condensate pipe is the most outstanding problem. The condensate pipe drains acidic water that is produced during the condensing process. These pipes are prone to freezing in winter and can cause the boiler to malfunction if they block.

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