Which is the Best Boiler for a Small House or Flat?

boiler flat

Getting the right boiler for a small home or flat with one bathroom is just as important as finding one powerful enough to meet the higher demands of a large home. Install a boiler that’s too powerful and you’ll see your energy bills begin to rise.

Smaller homes or flats with 1 bathroom and up to 10 radiators will be able to get their hot water and heating demands met with a Combi boiler. These are compact units that won’t take up too much space and can provide hot water on demand just when you need it.

Combi boilers commonly run on gas but electric Combis are available too and while they might be expensive to run they often come close to 100% efficiency.

The best way to find the most suitable Combi boiler for your small home or flat is by comparing the most trusted models on the market, which is exactly what we’ve done in this article:

Best Gas Combi Boiler: Ideal Logic Plus 24 vs Vaillant ecoTEC Pro 24
Best Electric Combi Boiler: Electromax vs THERMAflow

If you live in a 3 bedroom, 4 bedroom or 5 bedroom house, we’ve compared the most suitable boilers for them too.

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Best Gas Combi Boilers: Ideal vs Vaillant

Ideal and Vaillant are 2 of the most recognised, popular and trusted boiler brands around.

Ideal manufacture a range of Combi and System boilers, while Vaillant also offer Regular boilers on top. For this head-to-head we’ll be focussing on a Combi boiler manufactured by each brand.

So, let’s find out exactly what a Combi boiler is, how they work and why they’re different to System and Regular boilers.

What is a Combi Boiler?

Combi boilers are the only boiler type that has everything needed to provide your home with heating and hot water all wrapped into one unit. The other boiler types are System and Regular, which both require a cylinder to store the hot water once it’s been heated.

Combi boilers are the boiler of choice for new installations across the UK as they don’t take up as much space around the home, are highly efficient and provide instant hot water.

Battle of the Gas Combi Boilers: Ideal Logic Plus 24 vs Vaillant ecoTEC Pro 24

Let’s start this head-to-head by getting to know both boilers a little better, find out their key features in the table below:

Boiler Feature Ideal Logic plus 24 Vaillant ecoTEC Pro 24
Dimensions in mm (HxWxD) 700 x 395 x 278 720 x 440 x 338
ErP Efficiency Rating A Heat, A Water A Heat, A Water
Standard Warranty 7 years 2 years
Typical Price £755 £930
Mounting Wall mounted Wall mounted
kW Options 24kW 24kW
Flow Rate 14.5 l/m 11 l/m
Typical Installation Costs £500 – £1,000 £500 – £1,000


Typically, these 2 Combi boilers are reasonably priced, both sitting at under the £1,000 mark. The Ideal Logic Plus 24 comes in at the cheaper price but that alone shouldn’t make your mind up for you as there are still a lot of things to consider.

Energy Efficiency

April 2018 saw the introduction of Boiler Plus, a legislation which states that all gas Combi boilers manufactured and installed must have a minimum efficiency level of 92%. Boiler Plus coming into effect has meant that all gas Combi boilers are highly efficient which means that the Logic Plus and ecoTEC Pro won’t be too far apart.

To put that percentage into context, for every £1 spent on heating your home, only 8p is wasted. You can find out more with our guide to energy efficient boilers.


Not only does the Ideal Logic Plus have the lower price, it also boasts the longer standard warranty with 7 years on the parts and labour as well as 10 years on the heat exchanger. In comparison, Vaillant’s ecoTEC Plus has a 2 year warranty as standard that can be extended to 5 years when registered through Vaillant Advance.


Getting a boiler of the right size (in terms of output not physical dimensions) is one of the most important things to consider when purchasing a new boiler. Measured in kilowatts (kW) this shows how powerful the unit will be in terms of providing heating and hot water. Contrary to what you might think, you shouldn’t just go for the most powerful you can afford. Instead it’s all about getting a model suited to the heating and hot water demands of your home.

When it comes to a small home or flat with 1 bathroom and around 10 radiators then a boiler with an output of 24-28kW will be ideal. Both of these Combi boilers deliver an output of 24kW, which will be perfectly suited to smaller homes or flats.

Best Gas Combi for a Small House or Flat: The Winner

The Ideal Logic Plus 24 edges the comparison in just about every round so there’s no surprise that we’re making it the best gas Combi for a small flat or house. It offers a longer warranty, higher flow rate and more compact dimensions all at a cheaper price than the ecoTEC Pro 24.

Other Contenders

As we mentioned earlier, a Combi boiler with an output of 24-28kW will comfortably be able to meet the heating and hot water demands of a small home or flat with 1 bathroom and around 10 radiators. If you’d like to consider a different brand to the 2 we’ve compared above, then there are many other models that sit within that output range.

Boiler Model Output (kW) Typical Price
Worcester Bosch Greenstar 25Si Compact 25kW £1,016
Baxi EcoBlue Advance 24c 24kW £962
Viessmann B2TB Vitodens 222-F 26kW £2,700

Should gas not be an option in your property and oil be too expensive or impractical, then you could consider an electric boiler.

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Best Electric Combi Boilers

An electric boiler could be worth considering if you live in a smaller property with no access to the gas network, which is millions of homes across the UK. The downside to installing an electric boiler is that they’re more expensive to run than gas but there are still many benefits.

We’ve compared 2 of the most popular electric boilers on the market to help you find the right model for your home: Electromax vs THERMAflow.

What is an Electric Boiler?

Electric boilers are an option for homeowners living in small to medium sized properties and are able to produce hot water for heating and taps. Rather than running on fossil fuels such as gas or oil, they run – as the name suggests – on electricity. This means that they have no gas emissions and don’t require a flue but will be more expensive to run.

We’ve listed some of the advantages and disadvantages in the table below to help your decision making.

Advantages Disadvantages
High Efficiency High Running Costs
Lower Emissions Less Hot Water
Cheaper to Install Power Cuts

For homes with solar panels, you could have the added benefit of powering your electric boiler with the energy they generate, helping to reduce your energy bills.

Battle of the Electric Combi Boilers: Electromax vs THERMAflow

We’ve found 2 of the most suitable electric Combi boilers on the market and put them up against each other to help your decision making.

Boiler Model Electromax THERMAflow
Manufacturer Heatrae Sadia THERMAflow
Dimensions in mm (HxWxD)

1476 x 550 x 600 1590 x 550 x 690 to
1920 x 710 x 850
Efficiency Rating C Water, D Heating D Heating, C Hot Water
Standard Warranty 2years (10 years on cylinder) 1 year (25 years on cylinder)
Typical Price £1,800 – £2,000 £2,360 – £4,050
Mounting Floor-standing Floor-standing
kW Options 6, 9 10, 11, 13, 14, 16, 18
Typical Installation Costs £500 – £1,000 £500 – £1,000


There’s a pretty significant jump between the price of an Electromax compared to the THERMAflow, with the highest typical price of an Electromax being less than the lowest typical cost of a THERMAflow.

Energy Efficiency

Possibly the greatest benefit of installing an electric boiler is their efficiency, which can reach heights of 99% while gas boilers tend to sit at around 89-95%. This is because they don’t burn fossil fuels so no heat is lost as is the case with gas Combi boilers. So either of these electric boilers will help improve the efficiency of your home.

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Both warranties offer parts and labour on the boiler itself as well as giving a guarantee on the cylinder, which stores hot water. With the Electromax, you’ll be getting a 2 year warranty on the boiler with 10 years on the cylinder, while the THERMAflow has 1 year on the boiler with a massive 25 years on the cylinder.

All in all, we’ll give this round to THERMAflow as 25 years of cover, even though the boiler warranty is shorter than the Electromax, is something you don’t come across too often.


There’s a wider range of outputs to choose from with the THERMAflow but the outputs of the Electromax could well be enough to meet the heating and hot water demands of your home.

Best Electric Combi for a Small House or Flat: The Winner

There are some fairly significant differences between these electric boilers, from the potential price, to the warranty, right through to the outputs available. Thanks to having the cheaper price and longer warranty on the boiler itself, we’re crowning the Electromax as the best electric Combi for a small house or flat.

Other Contenders

There are several electric boiler manufacturers to choose from, with a range of outputs available depending on the hot water and heating demands of your home.

Manufacturer Boiler Model Available Outputs (kW) Energy Rating Average Price Standard Warranty
Electric Heating Company Comet 9, 12, 14.4 Hot Water: C Heating: D £2,571 2 years (10 years on cylinder)
Elnur Mattira MAC15 3-15kW Hot Water: C Heating: D £1,750 – £2,000 2 years (5 years on cylinder)
Electric Combi Boilers Co. Elektra EK.C 12kW (modulates from 2-12kW) Unknown £1,190 2 years

Gas or Electric Combi?

The gas Combi boilers we’ve compared tend to come at a much cheaper price than electric Combi boilers and also won’t cost as much to run. This in itself could make your mind up for you.

If you live in one of the 2 million homes across the UK that aren’t connected to the gas network then going electric is the next best solution. While the models might often be more expensive, they’re cheaper to install, have almost no noise during operation and can reach efficiencies of 99%.

What Next?

After finding the right boiler for your home, gas or electric, you’ll need a qualified engineer to carry out the installation. Installation costs can vary massively from installer to installer which is why we’re here to help you get the best deal possible.

Complete one of our simple online forms and you’ll get free quotes from up to 3 trusted engineers in your local area. You can then compare the quotes and decide which one to go with. Best of all, there’s no obligation whatsoever.

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If it’s time to replace your current boiler, use our free service to get quotes now