What is a Condensing Boiler? | How does a Condensing Boiler work?

The boilers are used all over the world for heating water and many other applications. They are most commonly used for residential and industrial applications. The boilers are most commonly used in steam power plants for steam generation. There are multiple types of boilers, and a condensing boiler is one of them. A condensing boiler runs on oil or gas fuel. These have more efficiency than non-condensing boilers. This article mainly explains different aspects of the condensing boiler.

What is a Condensing Boiler?

A condensing boiler is a type of boiler which is designed to improve the efficiency of energy. This is achieved by condensing water vapors into heat. The oil or gas uses as fuel to run the condensing boiler. These types of boilers have the capacity to recover lost heat from exhaust gases.

They have the capability to attain a high level of efficiency (usually 90% or more at a higher calorific value) by condensing the water vapors in the exhaust gas and improving its latent heat of vaporization. These condensed vapors leave the system as a liquid through a drain pipe.

condensing boiler

The maximum countries use the condensing boilers as a mandatory part or encouraged through financial reasons. The main difference between a non-condensing boiler and a condensing boiler is the amount of available heat that it generates. In addition, these boilers have the capacity to attain more than 90% energy efficiency.

The condensing boiler uses a separate flue system to avoid the waste of hot gases. This system extracts heat from the hot gas and utilizes this heat to heat the water that is returned from the central heating system. In other words, the actual boiler combustion chamber requires to perform less work.

Working of Condensing Boiler

The condensing technology is used in a condensing boiler to make better use of the generated heat.

condensing boiler working

This boiler uses oil or gas fuel to heat up your homes. As the fuel (i.e., oil or gas) burns, the exhaust gases generate and release from the flue pipes. In the case of non-condensable boilers, these exhaust gases discharge into the environment, and their heat energy is lost.

But in the case of the condensing boiler, the hot gas is extracted from the exhaust gases and transfers back to the system (which is called a primary circuit) via a heat exchanger. According to the type of the boiler, the primary circuit transfers this heat to hot water for domestic use or the heating circuit (radiator).

In the combination boilers, hot water generally heats up by a secondary heat exchanger called plate to plate heat exchanger. In the case of pure heating devices, the domestic hot water heats up and stores in storage tanks within the system.

Types of Condensing Boilers

The condensing boiler has the following major types:

  1. Combi Boiler
  2. System Boiler
  3. Conventional Boiler

1) Combi Boiler

The combi boiler is named after the fact that this boiler has a dual function (such as central heating and hot water device). These types of condensing boilers draw their required water directly from the main power source. Therefore, these boilers don’t need a water storage tank or a hot/cold water tank.

Combi Boiler

For maximum household applications, the combi boilers are the most profitable and efficient boilers than other types of condensing boilers. These boilers have the capacity to control both central heating and hot water.

The energy efficiencies of the combination boilers make them a best suitable device for the environmentally friendly property holder. You can get unlimited hot water anytime, anywhere by heating the water directly from the mainline and turning on the tap. These boilers need less space and less installation time because there is no need for an additional storage tank or cylinder.

Advantages of Combi Boiler

  1. The combi boilers are best suitable for low space houses
  2. It supplies a powerful shower without any extra pump
  3. This condensing boiler has an easy maintenance
  4. There is a very low pipework freezing risk
  5. It doesn’t require loft space
  6. It has a compact size
  7. These boilers have excellent efficiency
  8. Low cost compared to traditional boilers
  9. There is no need of a storage tank or cylinder
  10. The combi boiler needs low installation space
  11. It takes low time for installation.

Disadvantages of Combi Boiler

  1. These boilers are not the best choice for residences with low water pressure
  2. These boilers can’t run showers or two baths simultaneously
  3. The combi boiler has leakage issues which may lose water pressure
  4. These are not the best option for larger homes
  5. It requires an excellent mains pressure level
  6. It requires more time to fill a bath

2) System Boilers

These types of boilers are most commonly found in large households in which the demand for hot water is very high. In contrast to combi boilers, which can only heat water when required, system boilers have the capability to deliver the hot water throughout the house continuously.

system boiler

The system boiler uses a separate cylinder. Since it doesn’t have a hot water heat exchanger, it is designed to supply hot water by using a cylinder. It has a pump and an expansion vessel, which ensure the boiler installation in a closed system.

Since there is no need for a water tank, the system boiler eliminates the risk of frost damage and water leakage for homeowners and makes maintenance easier. A system boiler is suitable for large families with several bathrooms, especially if there is no space for the water tank.

Advantages of System Boiler

  • It has a compact design.
  • It can supply hot water to multiple bathrooms at the same time
  • The system boiler continuously supplies the hot water
  • It is an economical boiler.
  • This condensing boiler has a space-saving design
  • An expansion cistern doesn’t require for the system boiler
  • It can work with the solar thermal system, which makes it an energy-efficient choice
  • These boilers are options for large homes

Disadvantages of System Boilers

  1. It is true that a system boiler doesn’t need a storage tank, but it requires a large hot water cylinder
  2. It takes more installation space than a combi boiler
  3. The system boiler has large size than the combi boiler
  4. If the system boiler is not installed properly, it may lose heat
  5. Because this boiler has more parts than the combi boiler, therefore, it has more cost than the combi boiler.
  6. These types of boilers are not best for small houses

3) Conventional Boiler

The conventional boiler is also known as only a boiler, traditional boiler, open vent boiler, and regular boiler. Conventional boilers are best for people in areas with low water pressure.

In contrast to a combi boiler, it requires a separate water supply tank and a hot water storage tank. This design of the condensing boiler can supply several bathrooms simultaneously with a large amount of hot water.

Conventional Boiler

These are ideal boilers for older homes with large spaces. They have a large size than the combi and system boilers.

These boilers are not the best option if you have limited space in your home. It is better to remember that this type of device is more suitable for houses where a traditional heating system is already installed. You may not require changing the pipeline at all, but you may need to perform very slight changes if you do.  

Similar to a system boiler, you may use it with a solar system to lessen the ecological footprint and the energy costs.

Advantages of Conventional Boiler

  1. These boilers are best suitable for areas that have low water pressure
  2. They can supply hot water to multiple bathrooms at the same time
  3. It is compatible with the solar system

Disadvantages of Conventional Boiler

  1. It needs a separate hot water tank and a supply tank
  2. The conventional boiler has a large size than other types of the condensing boilers
  3. They require more space for installation
  4. These boilers need a large time to warm up the water
  5. The conventional boiler has complex and expansive installation

Why is a condensing boiler safer?

A non-condensing boiler usually extracts the room’s inner air. In contrast, a condensing boiler takes air directly from outside the room in which it is installed and sealed to heat up the room completely.

It represents that there is no chance to suck something into the boiler.

One more safety benefit of the condensing boiler is that in this boiler, condensate is treated via a pipe coupled with the sewage system so that there can be no risk of connection with the toxic substance.

What temperature should a condensing boiler be set at?

If the temperature of the condensing boiler is not set correctly, its efficiency will not reach up to the expected level. The goal of a condensing boiler is to ensure energy and heat savings. Therefore, you need to make sure that the condensing boiler is at the optimal temperature.

The critical temperature for central heating should be set to approx. 70°C and hot water to approx. 60°C.

Common condensing boiler problems

Technological progress increases the reliability of the boilers. But all types of boilers have different reliability, advantages, and disadvantages.

Condensing boilers supply a continuous flow of condensate. This condensate drains into the wastewater (as washing machines and sinks) of your house.

For safety reasons, the condensing boiler switches off automatically when the outlet blocks. In maximum cases, this problem occurs due to the frozen line of the condensate boiler.

This line frozen issue occurs when the boiler has a condenser pipe on the outside of the room and is exposed to low temperatures. It’s a fairly common issue during winter, but it’s easy to prevent and fix.

Differences between Condensing Boiler and Non-Condensing

Condensing BoilerNon-Condensing Boiler
The condensing boilers have a high initial cost.The non-condensing boilers have lower initial costs.
It has a less CO2 footprint It has a higher CO2 footprint
In this boiler, exhaust gases are recycled by the condensing heat exchanger, and their heat is utilizedIn this boiler, 30 percent heat of the combustion gases is wasted.
It has less temperature of the combustion product (i.e., 55°C)It has up to180°C temperature of combustion product
The condensing boiler may have more than one larger heat exchangerThe non-condensing boiler has only one heat exchanger and one combustion chamber
The condensing boiler is most efficient (up to 99%).The non-condensing boiler is less efficient (up to 78%).

How much does a condensing combi boiler cost?

The installation cost of the condensing boiler varies according to the brand and area where you live.

The normal cost of a condensing boiler varies from £490 to £1,800. You can also purchase an efficient model from the top brand (i.e., Worcester Bosch, Potterton, Valliant, or Baxi) for lower than £710. However, these boilers are best for small apartments but not best for the average household.

Condensing combi boiler Cost According to models

Boiler ModelAverage Price (without installation)
Viessmann Vitodens 100-W£910 to £1,000
Glow-worm Energy£700 to £910
Baxi EcoBlue Advance£900 to £1,400
Ideal Logic+£690 to £910
Vaillant ecoTEC Plus£900 to £1,500
Worcester Bosch Greenstar i£790 to £960

FAQ Section

What are the common problems of the boiler?

  • Boiler Not Heating Hot Water Enough 
  • Hot Water but No Heating 
  • No Power to Boiler 
  • Pilot Light Keeps Turning Off 
  • Boiler Not Responding to Thermostat
  • Frozen Condensate Pipe 
  • No Hot Water 
  • Noisy Boiler 
  • Radiator Faults 
  • Low Boiler Pressure 
  • Boiler Leaking 

Which type of Boiler do I need?

When looking for an alternative boiler, choose a boiler according to the requirements of your home. This is because every building has various heating needs and different boiler systems have some unique characteristics.

Generally, combination boilers are best for small apartments with only one bathroom, and household aquarium boilers (conventional and system boilers) are suitable for homes with more than one bathroom.

How long does condensing boiler last?

The average service life of a condensing boiler is from 14 to 20 years. However, the commercial cast iron boiler can last a long time, but its efficiency decreases over time.

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