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Which is the Best 24kW System Boiler?

Becky Mckay
By: Becky Mckay
Updated: 6th July 2022

Best 24kW system boiler

For properties with around 10 radiators and 2 bathrooms the best 24kW system boilers will comfortably provide enough central heating and domestic hot water. Our list of the best 24kW system boilers includes:

  • ATAG i24S
  • Baxi 824
  • Ideal Logic Max
  • Potterton Assure
  • Vaillant ecoTEC Plus 624
  • Worcester Bosch Greenstar 24i

Is a 24kW system boiler suited to my home?

A system boiler takes water directly from the mains, heats it up and then either circulates it around the central heating system or to the hot water cylinder, where it is stored until needed. As system boilers store hot water in a cylinder, they're perfectly suited to homes with a high demand hot water.

A fully-qualified heating engineer is the best person to recommend the most suitable heating system for the central heating and domestic hot water demands of your home. By completing our simple online form, you can get free quotes from engineers in your area.

The best 24kW system boilers

When looking for the best 24kW system boiler there are plenty to choose between.

Best 24kW System Boilers Seasonal Space Heating Efficiency ErP Rating Warranty
ATAG i24S 94% A 10 years
Baxi 824 93% A 10 years
Ideal Logic Max 94% A 10 years
Vaillant ecoTEC Plus 624 94% A 5 years
Worcester Bosch Greenstar 24i 94% A 7 years


ATAG are well known for the lengthy 10 year warranties they attach to all of their boilers, which shows exactly how much faith they have in their performance. As well as the warranty, the efficiency is amongst the highest when it comes to comparing the best 24kW system boilers, which will help to save you money on your energy bills.

  • Built-in ErP pump which ensures that the boiler is able to deliver the most efficient performance at all times
  • Compact dimensions that make it perfect for a cupboard fit (h700 x w440 x d355)
  • Simple to use controls
  • Extensive 10 year warranty

The ATAG iS range of system boilers also includes output ratings ranging from 15 kW right up to 40 kW.

Baxi 824

Baxi 800 system boilers are manufactured in the UK and are fitted with brass components of the highest quality. Baxi boilers are well known for their reliability and also perform to a highly efficient level.

  • Includes high-quality brass components
  • Fitted with an Adey Micro2 magnetic system filter which increases performance and helps to protect the unit
  • OpenTherm ready which makes it possible to take control of the heating from your smartphone or tablet
  • A low lift weight (29.5kg) could help to lower the installation costs
  • Available with a lengthy warranty of 10 years

An 18kW model is also available in the Baxi 800 range of system boilers.

Ideal Logic Max

Ideal's Logic Max range of system boilers build on the standards set by the Logic Plus to deliver an efficient, high performing heating system that's covered by a lengthy warranty.

  • A large digital display makes it easier to know exactly how your boiler is performing at any one time
  • Has a frost protection feature which will keep the heating running through even the coldest of conditions
  • Fully compatible with Ideal heating controls
  • Extensive 10 year warranty

The Logic Max range includes a number of outputs, with 15kW, 18kW and 30kW models all available in addition to the 24kW unit.

Vaillant ecoTEC Plus 624

Vaillant ecoTEC boilers are well known for their efficiency, which comes largely thanks to the stainless steel heat exchanger.

  • A stainless steel heat exchanger increases efficiency and will help to extend the life of the boiler
  • Built in two stage frost protection for reliable performance all year round
  • Quiet Mark accreditation which guarantees quiet performance during operation
  • Compact dimensions of 720 x 44 x 335 (HxWxD)that make it suitable for a cupboard fit
  • Wide modulation range of 1:6 which will help to increase efficiency and lower your energy bills further

Should a 24kW system boiler not be suitable for your home then the Vaillant ecoTEC Plus range of system boilers also includes lower outputs of 12, 15 and 18kW as well as larger outputs of 30 and 37 kW.

Worcester Bosch Greenstar 24i

Worcester Bosch has become one of the most popular boiler manufacturers in the UK and their Greenstar range is the most efficient yet.

  • Recycles heat from exhaust gases (would otherwise be lost) and modulates the output which can make the running costs 30% cheaper than some older boilers
  • Compatible with Greenskies solar panels which will heat the water in the cylinder using free renewable energy from the sun – further reducing your energy bills

The 24kW model is the highest output available in the Greenstar i range so if you're looking for a lower output then 9kW, 12kW, 15kW and 18kW outputs are also available.

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How much do 24kW system boilers cost?

A system boiler is likely to cost around £1,000 for the unit but you will also need to factor in the hot water cylinder as well as the installation too.

ATAG don't publish the price of their boilers but are likely to be the most expensive. The boilers from Baxi and Ideal are potentially the most affordable.

Best 24kW System Boilers Potential Cost (before installation)
ATAG i24S £2,000+
Baxi 824 £924
Ideal Logic Max £915
Vaillant ecoTEC Plus 624 £1,000
Worcester Bosch Greenstar 24i £995

Best 24kW system boilers for off-grid homes

A natural gas boiler isn't suitable for properties that aren't connected to the gas grid so if you live in an off-grid home then options include Liquified Petroleum Gas (LPG) and oil. Fortunately, some of the best 24kW system boilers are LPG compatible.

Best 24kW System Boilers LPG Compatible?
ATAG i24S Yes
Baxi 824 No
Ideal Logic Max No
Vaillant ecoTEC Plus 624 No
Worcester Bosch Greenstar 24i Yes

Only a couple of the best 24kW system boilers run on LPG so you might want to consider an oil boiler too. The Viessmann Vitorondens 200-T would be a suitable heating system.

Best 24kW System Oil Boilers Seasonal Space Heating Efficiency ErP Rating Warranty
Viessmann Vitorondens 200-T 97% A 10 years

Benefits of installing a system boiler

If you're looking for a modern heating system than a regular boiler (also known as conventional and heat-only boilers) then your choice comes down to a system or combi. While a combi is a compact cost-effective solution that doesn't need a water tank, system boilers are the better choice for homes with multiple bathrooms. These are some of the benefits of installing a system boiler:

  • If you have a regular boiler then a system boiler is a more modern alternative that is comes fitted with a pump to provide a quicker response when you turn the central heating on
  • As hot water is stored in a cylinder, they can meet higher demands for domestic hot water
  • Able to deliver hot water to more than a single bathroom at any one time without a drop in pressure
  • If you have a solar thermal system (or are considering one) then you can install a solar-compatible cylinder installed to help lower your energy bills

Looking to install a system boiler with a different output rating? Take a look at our other comparison articles:

How to get system boiler installation quotes

Finding a heating engineer to quote and install on your new boiler has never been easier. Using Boiler Guide, you can get free quotes from up to 3 heating engineers who are based in your local area.

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Becky Mckay

About the author

Becky Mckay

Becky is one of our home heating and renewable energy experts and has a wealth of experience writing about the world of heating.

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