What is a Condensing Boiler – Everything You Need to Know

The term “condensing boiler” is quite commonly used in the UK. Everyone having a gas or oil boiler installed in their home must be familiar with this term, especially if the boiler was installed after 2005. In 2005, it was made compulsory for homes, under the Building Regulations, to replace the old conventional gas boilers with the new condensing boiler. The same condition was also applied to oil boilers in 2007. Since then, the installation of conventional boilers has been totally discontinued in the entire UK. The reason behind imposing this change was to reduce the carbon footprint and to increase the energy efficiency of the boilers. 

While a reduction in carbon footprint makes it an environmentally friendly policy, the increased energy efficiency has significantly reduced the energy bill for the end users. The normal useful life of a boiler ranges between 10 to 15 years; hence, after the imposition of the policy of replacing old conventional boilers with condensing boilers, there should hardly be any boiler in the UK that is not a condensing boiler. Despite this fact, a very common question, often raised by consumers, is what a condensing boiler is, and how it is different from an old conventional boiler.

Keep reading this blog to find the correct and easy-to-understand answer to this very popular question.

Condensing Boiler – An Overview

A condensing boiler is a highly efficient type of boiler that saves a considerable amount of energy by utilizing the waste gases that would otherwise be expelled out of your home through the flue. In this way, the extra heat is reused for heating the water, which directly impacts the actual cost of gas or oil used by the boiler. This process of reusing the extra heat, which would otherwise be expelled out of your home, facilitates heating the water to the same temperature by using less volume of gas or electricity.

This has a dual impact. It increases the energy efficiency of your boiler and lowers the annual energy bill. On the other hand, the carbon footprint is drastically reduced. So, the main difference between a conventional old boiler and a condensing boiler is the reutilization of waste gases, which a traditional or non-condensing boiler used to throw out via flues. 

How to Know if You Have a Condensing or Traditional Boiler?

Although building regulations governing the installation of condensing boilers have been in place since 2005, it is still essential to determine whether your boiler is condensing or non-condensing. To make sure yours is a condensing boiler, you need to inspect the flue. To remind you, a flue is a pipe installed in your home to eject hot and waste gases produced by the boiler during water heating. In the case of a conventional or non-condensing boiler, this pipe (flue) used to be metallic, as it was meant to vent out very hot gases.

On the contrary, if you have a condensing boiler installed in your home, the flue pipe would be made up of plastic or a similar material, instead of metal. The reason is that the gases meant to be expelled in the case of a condensing boiler are far colder as compared to those of a non-condensing boiler. So, the simple test is to check the flu. If the boiler is metallic, it is non-condensing; if it is made of plastic, it is a condensing boiler.

Understanding the Heating Process of a Condensing Boiler 

For a better understanding of how the water is heated in a condensing boiler, it would be appropriate first to recall the heating process of a traditional or non-condensing boiler. 

How is Water Heated in A Non-Condensing Boiler?

• Gas or oil, depending on the type of boiler, is burned, which creates heat, through a hot flame.
• The heat generated by this hot flame is transferred to the Heat Exchanger, which is a compulsory component of every boiler. This is the component where the cold water, coming in from the main water supply of your home, is heated by the boiler. This heated water is then transported into the heating system of your home. 
• The burning process of gas or oil produces hot gases, which, in the case of a conventional boiler, are wasted and need to be expelled through the vent (flue). This waste and hot gas contain water vapors, which a condensing boiler can otherwise reuse.

How Water is Heated in a Condensing Boiler – The Difference 

The process of heating the cold water received in a condensing boiler from the main water supply is the same as that of a non-condensing boiler. The difference between them is the installation of a second heat exchanger. Here, the waste hot gases are reused instead of being released into the atmosphere:

• At the first heat exchanger, the process of heating the cold water is the same.
• After warming the cold water in the first heat exchanger, the waste and hot gases are not transported to the flues for expelling them out of the system. Instead, these are sent to the second heat exchanger for reutilization.
• At the second heat exchanger, the process of condensing comes into play. The hot gases from waste are full of water vapor. At this stage, they are cooled down. The method of cooling them down results in condensing the water vapor back into liquid form. This process simultaneously releases a lot of latent heat, which can be and is reused.
• This released latent heat is captured at the second heat exchanger, where the cold water, coming back into the boiler, is pre-heated when it enters the second heat exchanger. So, the boiler has to spend less amount of gas or oil to heat the water, which is already pre-heated, thus reducing the energy consumption and increasing the efficiency of the boiler. 
• Lastly, the much cooler waste gases are expelled from the system through the flue. Simultaneously, the condensed water, also known as “condensate,” is safely drained away into your home’s drainage system via a small plastic pipe. This condensed water is slightly acidic at this stage.
• Since the condensing boiler is capable of reusing heat, which otherwise would have been wasted, the required temperature level of heated water can be achieved with a significantly lower amount of energy, reducing the energy bill.

Difference in Energy Efficiency Rating 

There is a huge difference between the energy efficiency of a traditional non-condensing boiler as compared of the condensing boiler:

• The non-condensing boiler typically operates between 60% to 75% efficiency.
• The condensing boilers operate at an energy efficiency rate of around 92%. In most advanced condensing boilers, often rated “A”, the energy efficiency may be up to 94% to 98%. 
• In financial terms, a condensing boiler is capable of saving you around £200 - £300 annually.
• The energy efficiency rating of a non-condensing traditional boiler is usually “G”, whereas the most advanced condensing boilers are classified under “A” energy efficiency rating. 

Main Advantages of a Condensing Boiler

• It is a legal requirement in the UK, following the imposition of new Building Regulations in 2005. So, by installing a condensing boiler, this legal obligation is fulfilled.
• The energy consumption of a condensing boiler is far lower than that of a traditional non-condensing boiler. On average, you can save up to £200 - £300 annually in the shape of reduced energy bills, while using a modern A-rated condensing boiler.
• The reduced utilization of gas or oil results in far less production of Carbon Dioxide. This makes your home environment friendly.
• The latest condensing technology is widely used in almost all types of boilers, of all sizes and capacities. This technology is being used successfully in Combi Boilers, System Boilers, and Regular Boilers. While a combi boiler is suitable for small homes, a system boiler is normally used in households having 3 to 4 bathrooms. On the other hand, regular boilers are often used in homes having older radiator systems, which are not compatible with high water pressures. All these boilers now come with the condensing technology.
• The condensing boilers come in a compact model, which can be easily and safely installed in your kitchen cabinet. These are safer, quieter, and require less space for installation.

Disadvantages

Like any other new product, condensing boilers also have a couple of disadvantages, though not many serious ones:

• In cold areas, the possibility of freezing of the condensate pipe, which drains out the condensate water, is higher. This may result in the shutdown of the boiler. However, freezing of this pipe can be avoided by proper insulation or protecting it from a direct freezing environment.
• The initial cost of a condensing boiler is usually higher than compared of a traditional boiler. However, the reduced energy bills and compliance with the building regulations may compensate for the initial upfront cost in the long run.
• Regular and annual maintenance is higher for a condensing boiler as compared to a traditional non-condensing boiler. However, timely repair and maintenance may save you quite a bit of extra expenses.

Important

• All condensing boilers must be installed and subsequently maintained by a Gas Safe Registered Engineer. 
• At the time of replacing the old non-condensing traditional boilers, you may have to obtain approval from the relevant building control office in your area.
• Under the provisions of the Boiler Plus Regulations of 2018, new installations have to include Energy Efficient Controls, such as weather compensation and programmable thermostats. 

Conclusion

Under the building regulations, imposed by the UK Government in 2005, all homes are required to install condensing boilers. In other words, since then, the installation of traditional non-condensing boilers has been discontinued. The purpose of these regulations is to reduce the carbon footprint, as the old boilers generate a large quantity of Carbon Dioxide. Reduction in consumer energy bills by installing a condensing boiler is an added advantage of these regulations. 

The condensing boilers are similar to traditional boilers, but the advantage of the new technology is that it utilizes the waste hot gases, which were being expelled out through flues, not only adding to pollution but also increasing the energy bills. The new technology of condensing boilers is capable of reusing the waste hot gases to pre-warm the colder water entering back into the boiler, causing less energy consumption to heat the water to the same temperature.