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Which is the Best 28kW System Boiler?

Becky Mckay
By: Becky Mckay
Updated: 18th January 2024

Best 28kW System Boiler

A 28kW system boiler is perfect for homes with around 15 radiators.

They’re also a great option if you have two or more bathrooms. This is thanks to the hot water cylinder which stores hot water until you need it. So no matter how many people need hot water at one time, they’ll all get a strong flow rate.

Only two system boilers have an output rating of exactly 28 kW:

  • Baxi Megaflo
  • Navien NCB

What is a system boiler?

A system boiler sits somewhere between combi and regular boilers.

Most of the parts it needs to heat the home are within the boiler itself (like a combi). However, they also need a hot water cylinder (like a regular boiler) to store the hot water. Unlike a regular boiler, there's no need for a cold water or expansion tank in the loft as they take water directly from the mains.

By working in this way, system boilers meet high demand for heating and hot water. Great news for larger properties.

If a heating engineer recommends a system boiler, then there are a number of benefits:

  • More straightforward installation compared to regular boilers
  • By storing domestic hot water in a cylinder, system boilers are able to meet higher demand for hot water – ideal for large and busy homes
  • Deliver water to taps and showers at a high pressure
  • Thanks to being fitted with a pump they're able to respond to you turning on the central heating much quicker than older heating systems
  • 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

Is a 28kW system boiler right for my home?

When a combi boiler simply won't do, a 28 kW system boiler is a great alternative.

They can heat large homes with up to 20 radiators and deliver hot water to more than 1 tap or shower at a time. So, if you have 2-3 bathrooms and live in a semi-detached home, a system boiler is worth considering.

However, you will need a hot water cylinder as well as the boiler. This will take up more space but is definitely worth it if you have more than 1 bathroom.

To find out the best idea of the ideal output rating for your home, you should hire a Gas Safe registered engineer. With Boiler Guide, you can get free quotes from heating engineers based in your area, who will take a look around your property and provide you with a comprehensive quote, let you know exactly the type of heating system you need and answer any questions.

Best 28kW system boilers

Best 28kW System Boilers Seasonal Space Heating Efficiency ErP Rating Warranty
Baxi Megaflo 92% A 7 years
Navien NCB 93% A 7 years

Baxi Megaflo System 28

Baxi Megaflo System 28
Baxi have built up a great reputation for their boilers with both heating engineers and homeowners. Their Megaflo range of system boilers are highly efficient, are made of quality brass components and are covered by an extensive 7 year warranty.

  • Frost protection for units installed in garages and lofts
  • Front access which speeds up servicing and potentially lower costs
  • A range of flue options for flexible installation
  • Compatible with the Megaflo Eco cylinder – an industry-leading hot water cylinder
  • Endorsed by the Energy Saving Trust

The Baxi Megaflo range of system boilers includes a number of different outputs, including 15 kW, 18 kW, 24 kW and 32 kW.

Navien NCB 28

Navien NCB 28
Navien are a more recent addition to the UK boiler market than the other manufacturers and they've quickly become a manufacturer worth considering. The Navien NCB 28 kW system boiler is highly efficient, boasts high-quality components and comes with a lengthy 7 year warranty.

  • Stainless steel heat exchanger for increased efficiency and extended boiler lifetime
  • A lengthy flue makes installation more flexible to give you greater chance of where to have the unit installed
  • A blue touchscreen display offers you greater control while also showing clear messages about the status and efficient running of the unit
  • OpenTherm ready which can help to lower the installation costs

The NCB System range also includes output ratings of 20 kW, 23 kW and 33 kW.

Could a different output suit my home?

You’re pretty limited for choice when comparing 28 kW combi boilers. But they may not be your only option.

Homes with between 15 and 20 radiators can consider a system boiler with an output between 27 kW and 40 kW. This will certainly give you more options.

However, it’s important to install a boiler that matches the heating demands of your home. Rather than going for the most powerful boiler. The best way to do this is by getting the expert opinion of a local heating engineer.

Best 27-40 kW Boilers Output Rating
Intergas Compact HRE SB 27 kW
Vaillant ecoTEC Plus 630 30.4 kW
Ideal Vogue Max System 32 kW
ATAG i40S 38.8 kW

How much do 28kW system boilers cost?

A system boiler can typically cost between £500 – £3,500 before installation with our list of the best 28 kW system boilers ranging from around £870 up to £1,030.

Best 28kW System Boilers Potential Cost (before installation)
Baxi Megaflo £870 – £1,030
Navien NCB £995

In addition to the system boiler, you will also need a hot water cylinder to store the hot water. Unvented cylinders are widely recommended by heating engineers as they offer much more flexible installation over traditional vented cylinders – find out the Best Unvented Cylinders.

Best off-grid 28 kW system boilers

All of these system boilers run on natural gas which means that your property will have to be connected to the gas network. However, this doesn't mean that if you live off-grid then you can't enjoy the benefits of the best 28 kW system boilers as some run on LPG – a gas that can be stored onsite.

Best 28kW System Boilers LPG Compatible?
Baxi Megaflo No
Navien NCB Yes

LPG isn't the only option for off-grid homes, there's also oil. A number of manufacturers offer system boilers that run on oil that are suitable for semi-detached homes, including Firebird, Navien, Viessmann and Worcester Bosch.

Oil System Boilers (28kW – 34kW) Output Rating Efficiency Warranty
Firebird Envirogreen Slimline Systempac C35 35 kW 92.6% 2 years
Navien LCB700 28 kW 93% 10 years
Viessmann Vitirondens 200-T 28kW 97% 10 years
Worcester Bosch Greenstar Danesmoor 32 kW 91% 2 years

Get free system boiler installation quotes

If the time has come for you to find a new boiler, then finding a fully-qualified local boiler installer has never been easier. You can get free quotes from up to 3 heating engineers in your area by taking a moment to complete our online form. Simply telling us about the work you need completing.

With your quotes in hand, you can be confident that you're getting the most competitive price for the installation of your new boiler.

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Becky Mckay

About the author

Becky Mckay

Becky has been a writer at Boiler Guide since 2021. Her vast boiler knowledge means she’s ready to help with any home heating query, big or small!

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