Best Compact (Small) Combi Boilers to Buy in 2024

If you’re looking for the best small boiler, then it’s likely that you’re concerned about space in your home, and how much space a boiler installation might take up. 

Luckily, combi boilers operate central heating and domestic hot water from one unit and most combi boilers will fit discreetly inside a standard kitchen cupboard. 

While combi boiler units are usually bigger than system or conventional boilers, a combi boiler will still take up the least space in your home. This is because there are no additional units to make space for, such as a hot water cylinder or cold water tank which run alongside other boiler types. 

If space in your home is precious, then this article is here to highlight the most compact combi boilers and their key features to help you determine the best small combi boiler for your home. 

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From across the boiler manufacturing industry, we’ve identified the 5 best combi boiler ranges with the smallest dimensions, and listed below from the smallest to the biggest.

Alongside their height, width and depth (HxWxD), we’ve also provided some key specifications which might help you determine the right model for you. 

The domestic hot water (DHW) output indicates how powerful the boiler is and how well it will meet your energy demands. Combi boilers have a second output rating for central heating (CH), but the domestic hot water output will give a better indication of the boiler's capacity to meet your energy needs since it takes more power to provide this.

A boiler’s efficiency lets you know how well the boiler can convert fuel into usable energy. Thanks to modern condensing technology, a new boiler will meet a minimum efficiency rating of 92%. This means that for every £1 spent on energy, only 8p is wasted. 

Once a boiler is installed, the boiler manufacturer will issue a warranty period that will usually cover the costs of any service repairs, including the associated part and labour. The longer the warranty period, the more assured you can be of the boiler's reliability. 

We’ve also provided the typical price range for the new boiler itself, excluding installation. 

Besides finding the space to install a new combi boiler, it's also important to find the right installer and ensure you are paying a reasonable price. With so many options out there, how can you know that you’re not overpaying on installation costs?

By comparing quotes you can make sure that you won't overpay for your new boiler installation.

Comparing quotes from installers can take hours and be very stressful when done alone.

Luckily, GreenMatch can connect you with up to 3 approved local installers for free!

Intergas is Dutch-originated, founded in 1939. This is a lesser-known brand compared to the likes of Worcester Bosch or Ideal, but don’t be put off. Since 1939, Intergas has become a company that forefronts efficiency and innovation. In 1996, Intergass pioneered the first bithermal heat exchanger, which is a standard boiler component across the industry today.

The Compact Eco RF range by Intergas features the smallest boiler in the industry, the Eco RF 24. With a rated heating output of 18kW, it will suit smaller homes with up to 10 radiators and 1 bathroom. 

The Eco RF 30 and the Eco RF 36 have slightly larger dimensions but with a heating output of 23kW and 27kW respectively, they can meet the energy demands of slightly larger homes with up to 15 radiators and 1 bathroom. The range also comes with the maximum warranty offered by the company of 10 years, letting you know that they have full confidence in this model.

Glow-worm is a longstanding boiler manufacturer in the UK. They were established more than 80 years ago but nowadays, they are owned by Vaillant, one of the most reputable brands in the UK. 

The Compact combi boiler is Glow-worm’s smallest and lightest boiler. This makes it great for homes wanting to save space. With an output range of 24kW-28kW, it will meet the demands of small-to-medium-sized homes with up to 15 radiators. 

This boiler is wall-mounted and will easily fit inside a kitchen unit. Its low noise levels also mean you won’t be disturbed while it runs. This model is also available to run on LPG fuel for homes off the gas grid. 

Another contribution to the list from Worcester Bosch, the Greenstar CDi Compact. This features the smallest boilers to come from Bosch’s range while still reaching the highest outputs from the 5 boilers in this list. 

Therefore, this compact but powerful boiler makes a great option for medium and large-sized homes with up to 20 radiators and up to 2 bathrooms, without compromising lots of space in your home. 

This boiler is compatible with multiple controls including Bosch’s own smart controls. It also boasts exceptional hot water flow rates of up to 14.7 litres per minute which can fill a kitchen sink in 37 seconds, according to Bosch. 

Worcester Bosch is perhaps the most reputable brand in the UK. Since 1962, the company has become synonymous with high-performing and reliable products and services. Bosch’s popular Greenstar range has achieved a Which? Best Buy award for 7 years running.

Both models within the Greenstar Si Compact boiler range come with compact dimensions and will fit inside a kitchen cupboard with ease. The 25Si Compact with a heating output of 25kW is best suited to smaller homes whereas the 30Si Compact can provide for small-to-medium sized homes with 1 bathroom.  

Bosch offers a wide range of heating controls to choose from which allows for greater comfort including standard controls and wireless internet controls. This range is also compatible with 20% hydrogen blends and comes with LPG alternatives for homes off the gas grid. 

Established in the UK in 1906, Ideal is among the top players in the UK domestic heating industry. The brand is known especially for its affordable price points and it offers some of the longest warranty periods around, with options up to 12 years. 

The Logic+ from Ideal is powerful enough to provide ample heat and hot water to small-to-medium homes. This popular range is decorated with awards including the Good Housekeeping Reader Recommended Status in 2013 and 2017 and is credited by Which? as a trusted trader for warranty repair and service. 

The Logic+ features Ideal’s highly efficient, patented heat exchanger with its own 10-year warranty. It’s also future-proof as it’s compatible with a 20% hydrogen blend and is available to run on LPG. 

This addition to the list is a 2-for-1 special, as the Ideal Logic Max comes with the same compact dimensions and available outputs as the Logic+. The main difference is the Logic Max features an additional system filter which will prolong the life of your boiler by preventing waste debris from building up through your system.  

Not sure which boiler will be best for your home? Before going ahead with a new installation, we recommend consulting a professional heating engineer who can offer advice based on your home's unique specifications. This will give you the best insight into the best new boiler for your home and the potential installation costs. 

Fill in our 30-second form, and we will connect you with up to 3 local installers. Multiple installers means you’ll receive multiple quotes that you can compare to get the best deal.

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The smallest boiler available in the UK is the Intergas Compact ECO RF 24. This is a wall-mounted compact boiler that will fit in a standard kitchen cupboard with ease. Additionally, its vacuum insulation technology means it will maintain very low noise levels so you can have it running in the kitchen and not be disturbed by any noise. 

The Eco RF 24 has the smallest combi boiler dimensions in terms of height (590mm) and depth (240mm), both of which fall far below the average combi boiler dimensions. 

These small combi boiler dimensions will easily fit into a standard kitchen cupboard which is usually no shorter than 760mm in height, 300mm deep, and at least 400mm wide. 

When you're looking to install a combi boiler, it’s important to consider your home's energy needs. This means figuring out how much hot water and how much heating you need.

Combi boilers have two heat outputs: one for domestic hot water and the other for central heating. Producing hot water requires more effort and, therefore, more heat than heating the radiators, so it’s usually the hot water output that determines your choice of boiler.

With this in mind, the smallest available output for domestic hot water and central heating from our list of boilers is also the Intergas Compact ECO RF 24. This model has an available output of 22kW for domestic hot water and 18kW for central heating.

This makes it ideal for small homes wishing to save space, with enough power to provide heat and hot water to homes with up to 10 radiators and 1 bathroom.

For some further context, we calculated the average height, width and depth of combi boilers of all fuel types across the market. We found the average combi boiler dimensions are: 

Height: 819mm | Width: 443mm | Depth: 333mm

These averages will still fit inside most standard wall-mounted kitchen units which is good news if you’re looking for somewhere discreet to keep your new boiler. Consulting a licensed heating engineer can give you the best idea as to where a new boiler will fit inside your home, as they can also advise you on any clearance space the new boiler might need once it’s installed. 

Rather than putting yourself through the painstaking task of researching individual heating engineers and receiving their itemised quotes, we can help you get straight to the business of installing through our quotes service. 

Fill in our 30-second form, and we will connect you with up to 3 local installers. They can then help you determine the right boiler dimensions and output size for your home space. 

With multiple quotes, you can take advantage of the best deals in your area, helping you to truly make the most of your savings.