If you need to fit a boiler in a tight spot, it'll need to have compact dimensions. Here's our guide to picking the best boiler with pint-sized proportions, without compromising on power.
Are you looking for a small boiler?
Not just any small boiler, one that's compact, but'll deliver all the hot water and heat your heart desires?
When it comes to fulfilling your needs, size doesn’t matter – as long as you don’t have too many bathrooms.
The quick answer? The smallest boiler in terms of dimensions is the Worcester Bosch CDi Compact, designed to fit into kitchen cupboards. Check the latest price here.
Compact vs. Small Combi Boilers
You may assume that compact and small are used interchangeably, but in the context of boilers, they mean slightly different things.
...How are they defined?
Small Boilers
A small boiler relates to the boiler's heat or power output (measured in Kilowatts) i.e. it is considered to have a “small” heat output or one that is adequate for properties with smaller hot water demands. As the philosopher Jay-Z would put it, “You know the type: loud as a motorbike but wouldn't bust a grape in a fruit fight.”
Check our reviews of some of the smallest boilers on the market (ranging from 25 kW – 30 kW):
Compact Boilers
A compact boiler relates to the dimensions of the boiler unit itself. These boilers would stress that it’s not the size of the dog in the fight, but the size of the fight in the dog that matters.
The good news is that many 'small' boilers are also compact too, which makes perfect sense considering small boilers are usually installed in smaller properties with limited space.
Compact boilers are ideal for people wanting a boiler that will fit in a kitchen cupboard or a comparable small space.
When it comes to boilers, size really does matter.
Read our in-depth Worcester Bosch Greenstar CDi Compact Review.
What is considered a Small Boiler?
For those that live in a small property such as a flat or small house, a boiler size with a power output between 24kW – 28kW is considered to be a small boiler and adequate. If you’re a witch in the woods, these boilers are fine.
Sometimes these small boilers will be sufficient for a 3-bedroom or bungalow too, it largely depends on the number of radiators you have and your hot water usage. Radiator collectors might want to keep looking.
Since they provide both hot water and heating, combi boilers have two separate output ratings:
Central Heating (CH) Output
Domestic Hot Water (DHW) Output
Typically, boiler brands will offer their boilers in a range of different sizes (the Worcester Bosch 8000 for example comes in 30kW, right up to 50kW!)
To determine how powerful it needs to be, the main factors when it comes to combi boilers are the number of hot water outlets your home has (such as bathrooms, showers etc).
For example, if you live in a small bungalow with one bath/shower, then a small combi boiler is probably going to be recommended.
However, if you live in a home with many rooms, with multiple bathrooms, then a large-sized boiler will be required to meet the heating demands. Unless you make your kids shower with cold water.
So, what size boiler do you need?
You can use your current central heating setup to give you an idea of what size boiler you require.
This is based on the number of bathrooms on your property (or you can find out using our free tool):
Bathrooms/showers | Ideal size/Boiler type | |
1 | 24kW-28kW Combi | |
2 | 28kW -32kW Combi | |
3 | Storage Combi or System | |
4+ | Storage Combi or System |
Please note: Combi boilers are not recommended for homes where there is a very high demand for hot water. If you have multiple bathrooms, consider a hybrid/storage combi boiler, such as the Viessmann 111.
What makes the Best Small Boilers?
The majority of boiler manufacturers offer their boilers in a range of different sizes, but how do you know which one to choose? Unlike flavours of ice cream in a shop, there’s no trying out different boilers until you’ve made your choice.
Ultimately, the same factors apply as they would for any other type of boiler – you want your boiler to be reliable, offer maximum value or money and last the test of time.
Here is a good summary of the factors we always consider when recommending new boilers (regardless of their size):
#1 – Which? Best Buys
The consumer association was established back in 1963 and their Which? Best Buy Awards are highly respected by both consumers and industry insiders.
Their reviews and ratings are based on feedback from installers, consumers, and a thorough testing process. In some way, they do the flavour testing for you.
One of the leading boiler brands, Worcester Bosch (and also ranked number 1 in our best boiler brands list) has maintained the Which? Best Buy Award for 10 years in a row. Odds are that the 11th year is not going to be a whole lot different.
More specifically, the brand was awarded top marks for its build quality and availability of parts and spares.
#2 – The Warranty Period
The warranty period is an essential part of shopping for a new boiler since you want to be covered for parts and repairs in the unfortunate event that something goes wrong.
Ideally, you want the warranty period to be as long as possible. Or at least longer than the average celebrity marriage.
The majority of boiler brands offer a warranty of 5 to 10 years, with Worcester Bosch offering a market-leading 10-year guarantee (when you buy through Heatable).
That’s correct, they offer a 10-year guarantee and not just a warranty.
...What’s the difference?
A guarantee is an agreement from the brand that they will attend to your property and repair or offer a new boiler within a reasonable timeframe.
If only those celebrity marriages came with a guarantee.
Most other brands just offer a warranty as standard, this is an agreement to investigate the problem but is not an unconditional agreement to fix or repair it for free.
If you live in an average-sized home, see our guide on choosing the best boiler for a 3-bedroom house.
#3 – Efficiency Ratings
The efficiency rating isn’t just important for those who care about the environment, but a high efficiency also means you will use less energy and therefore save money on your heating bills. So you can care about the environment, money, or both.
The highest efficiency gas combi boilers are now available with an A-rated efficiency rating of 94%, meaning that for every £1 you spend, only 6p is wasted. Compare that to your education, and it’s even more impressive.
Want to have your boiler moved to a different location? Check out our "cost of moving boiler" guide.
#4 – Availability of Parts
What if your boiler breaks down due to a faulty part? Such as a faulty heat exchanger or perhaps even a faulty diverter valve?
Sometimes a boiler can only be repaired and brought back to a functioning state by replacing a faulty part. Therefore, you want new boiler parts to be available and delivered to your engineer quickly.
That is why it is essential to secure yourself a boiler with a well-established network and parts that are easily accessible in the UK.
That bespoke Italian hand-crafted boiler sounds fancy, until you need to wait for a blacksmith to custom make you a replacement part.
Learn about the important factors to consider when having a new combi boiler installed.
The Best Small Combi Boiler
With the above factors in mind, here are our picks of the best small boilers currently on offer, providing reliability, value for money and substantial warranty periods. All of them provide warm water, too.
Worcester Bosch Greenstar 4000 Combi Boiler
Worcester Bosch is one of the most well-established and renowned boiler brands in the UK, well respected by installers and homeowners alike (that’s why we ranked them as #1 in our list of the top boiler manufacturers).
The Greenstar 4000 is a brand new arrival to the Worcester Bosch range of combi boilers, designed to replace the best-selling Greenstar i range. The Worcester Bosch 4000 offers everything the i range did but with some major improvements, including a quieter operation and a higher hot water output.
The 4000 benefits from a new, sleek curved edge case, user-friendly digital display and easy-to-use push control buttons, a major improvement on the boring square boxes of old.
See our boiler size calculator for more details on kW's.
The Greenstar 40000 is considered Worcester Boschs mid-range combi boiler range, offering an A-rating for efficiency, an extremely user-friendly digital interface and awarded the Which? Best Buy award.
Looking for a small boiler that’s also compact? So much so that it can fit in most kitchen cupboards? Check out the Worcester Bosch CDi Compact.
Summary of the 4000:
High-efficiency A-rated boiler
Available in 25kW or 30kW
Which? Best Buy Award winner for 10 consecutive years
10-year guarantee (not just a short warranty)
Get a Small Boiler Quote Today
Here’s why you should choose Heatable when shopping for a new boiler:
Gas Safe installation within 24 hours
Thousands of happy customers – an average score of 4.9 on Trustpilot (that’s better than the market leader).
Price match guarantee – if you find a cheaper quote, we will match (must be like for like)
Multiple payment options - interest-free boiler finance available
10-year guarantee
Fixed price guarantee – no hidden costs
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Heat happy.
