• June 16, 2020

Boiler Efficiency: How Efficient are Modern Condensing Boilers?

Boiler Efficiency: How Efficient are Modern Condensing Boilers?

Boiler Efficiency: How Efficient are Modern Condensing Boilers? 150 150

Boiler Efficiency: How Efficient are Modern Condensing Boilers? Compare Boiler Quotes

Today we are looking at the factors which make an efficient boiler. Overall, modern boilers are far more efficient than even 10 years ago. Today, most modern combi boilers are condensing systems and so we’ll be looking at these systems today and explaining this further for you. 


So What is a Condensing Boiler?

Boiler Efficiency: How Efficient are Modern Condensing Boilers? Compare Boiler QuotesIf you’re looking into and trying to decide on the best boiler type for your home, you may be getting slightly confused with all the options out there. 

We like to explain things for you so that you can make the best choice so let’s look into these types of boiler systems.

In gas boiler systems,  the heated gases pass through the boiler’s heat exchange surface, transferring the generated energy to the radiators. Once it’s all heated, the extra combustion gases are released into the atmosphere through the boiler’s flue.

The issue with this is that a certain amount of heat is lost here because the gases as well as a large amount of steam gets forced out of the flue. This leads to a lot of lost heat and energy just being released out of the flue. But why can’t we use this excess heat?

Well this is where a condensing boiler becomes the smart, ecological, and cost-effective choice. This is because they recirculate this wasted heat back into the system, therefore requiring less energy to heat your home as a percentage is recycled.


The Boiler Efficiency of Combi Boilers


The modern condensing boilers are far more efficient than even 5 year old boilers. A brand-new condensing combi boiler made by or recommended manufacturers is going to be significantly more efficient than a 2015 boiler.

In measurable terms, a high efficiency A-rated boiler will convert up to 94% of consumed energy into usable heat. That means only 6% of the energy is wasted. If, however, you have an old inefficient boiler, you will be wasting 20% to 35% of energy and that makes a huge difference in bills. 

The reason this is so important is that depending on your energy consumption behaviour, your gas central heating system probably accounts for at least 50% of your yearly energy bill. 


Main Types of Condensing Boilers

Boiler Efficiency: How Efficient are Modern Condensing Boilers? Compare Boiler QuotesThere are two main types of condensing boilers: system boilers and combi boilers. The system boiler is a good choice for larger houses or for houses that have low water pressure. The combi boiler is the ideal choice for houses that require heating on demand.


There are various types of combi and system boilers but below is a simple example of the various types:


  • Wall mounted boilers: Sometimes also referred to as mounted boilers, this type of condensing boilers is very convenient because of their smaller size and because they can fit alongside a modular boiler arrangement.
  • Floor boilers: Also called a floor standing boiler or a floor mounted boiler, this type of boiler is larger than wall boilers and can produce a greater volume of hot water.
  • Single circuit boilers: The pipe system is a single closed circuit which means that there is a single main feed through which the water enters and exits the boiler. The risk with this type of heating installation is that if it is not properly balanced, then it will heat the house unevenly depending on the circuit the hot water makes.
  • Double circuit boilers: This type of boiler system has two separate pipelines, one that takes the heated water away from the boiler and heats the house and the second that moves the water toward the boiler to be reheated. This type of boiler is properly balanced and can heat the entire house to a similar degree.


Example of Some Efficient Systems:


Below is a list of some of the efficient systems available as of May 2020.

There are so many systems on the market that it is probably best to look through our website and see if there are any other efficient systems that would be suitable for your home.

Model Efficiency Heating output
Ideal Logic Heat + 89.5% 15kW
Vaillant ecoTEC Plus 15 93% 15kW
Worcester Greenstar Ri 15i 92% 15kW
Viessmann Vitodens 100-W 94% 30kW


How Efficient is my Boiler Likely to Be? 

Boiler Efficiency: How Efficient are Modern Condensing Boilers? Compare Boiler Quotes

Boilers have efficiency ratings of A-G much like other appliance ratings. Nowadays, modern boilers have to be A rated in order to be allowed on the UK market. Although it is hard to review older boilers, in general the below information should be accurate enough to discern the advances in boiler efficiency.


Ratings System:


  • A – 90% and above
  • B – 86-90%
  • C – 82-86%
  • D – 78-82%
  • E – 74-78%
  • F – 70-74%
  • G – below 70%

Older Boiler Efficiencies:


  • Over 25 years old: 60% efficient
  • 20 years old: 70% efficient
  • 15 years old 80% efficient
  • 10+ years old 85% efficient

As you can see, modern boilers are far more efficient and with up to 40% efficiency giants over the past quarter century, your bills will be significantly lower with a new system.




As with most things, modern technology has allowed us to create more advances in heat recuperation and energy efficiency. With the world moving closer and closer to a more green alternative, boiler companies either have to adapt to the times and build better systems, or lose out to newer alternatives. With up to 96% efficient systems however,they’re on the right track and the companies today have nothing to worry about from these alternatives in the near future. 

If you are indeed looking for a new boiler system and would like to get a personalised quote for our next new system, then please visit our partner site boilercentral.com.

By using this system all you need to do is answer a few simple questions about your home and get a quick and accurate quote. 

Once you’ve done this, you can choose the boiler that’s right for you, and book an installation date that’s convenient for you. Oh, and if you need it there’s flexible financing too.

Boiler Central also offers boiler cover, which starts at £13.99 and is great for systems out of warranty. You can cover items such as the electrics, lost keys, and all your central heating. 


Thanks again for reading and check back often for more articles.

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