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Last updated on January 15th, 2024 at 10:20 am

When it’s time to replace your boiler, you’re not just buying a new appliance; you’re investing in your home’s comfort and efficiency. We understand it’s a significant decision that can be both daunting and confusing.

That’s why Warmable have put together a guide that’ll walk you through everything you need to know to find the best replacement boiler for your home. We’ll cover boiler types, features and tips to ensure you make an informed choice that suits your needs and budget.


What Types of Boilers Are There?


Exploring the different types of boilers can narrow down our choices significantly. There are three main categories most homeowners choose from: combi, system, and conventional boilers. Each comes with its unique benefits and is suitable for various homes and lifestyles.

Combi Boilers

Combi Boilers are a popular choice for small to medium-sized properties. They provide heating and hot water without the need for a separate water tank, saving you valuable space. The compact size and efficiency of combi boilers make them a common favorite, especially for homes with limited space.

  • Space-saving design
  • Ideal for smaller homes
  • Provides hot water on demand

System Boilers

For larger homes with multiple bathrooms, a system boiler might be the better option. Unlike combi boilers, they do require a cylinder for storing hot water, but system boilers don’t need a loft tank, which still frees up some space.

  • Perfect for high water demand
  • Compatible with solar thermal systems
  • No tank in the loft required

Conventional Boilers

Also known as open vent or regular boilers, conventional boilers are perfect for homes that already have a traditional heating and hot water system in place. These boilers are typically suited for older homes that might not be able to accommodate the pressure of modern boilers.

  • Ideal for traditional systems
  • Fit for older homes
  • Can handle multiple taps being used simultaneously

As we consider our home’s size and hot water needs, one of these boiler types will likely stand out as the most efficient option. Remember to factor in the availability of space for any necessary tanks or cylinders, as this could heavily influence our decision.


What Factors Should I Consider When Choosing A Replacement Boiler?


When looking for for the perfect replacement boiler, there are several key factors you must take into account to ensure you make an informed decision. Energy efficiency is paramount and should top your list of considerations. A more efficient boiler can drastically reduce our carbon footprint and monthly energy bills. Look for a boiler with a high Efficiency Rating, typically an ‘A’ rating on the ErP (Energy related Products Directive) scale.

The size of the boiler is another crucial aspect to consider. This isn’t just the physical dimensions but also its output capacity, which needs to be matched to the size of our property and heating requirements. A boiler that’s too powerful for our home will result in wasted energy, whereas one that’s underpowered will struggle to heat our space effectively.

Bxear in mind the boiler’s lifespan; a high-quality, durable boiler may be more expensive initially but can save us money in the long run. In choosing the right boiler, we should also contemplate the following:

  • Compatibility with our existing heating system
  • The hot water flow rate, particularly if multiple bathrooms will be in use simultaneously
  • Future-proofing features, like smart controls for energy usage monitoring
  • Installation complexity and the associated costs

Let’s not forget the warranty and aftercare services offered by manufacturers. Having an extensive warranty and boiler insurance can offer peace of mind, knowing that any issues will be addressed without incurring additional costs.


What Efficiency Ratings


When exploring replacement boilers, efficiency ratings are crucial. They give us an indication of how much energy is converted into heat and how much is wasted. In the UK, boiler efficiency is rated by the Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK) scale, which uses percentages to show just how efficient a boiler is at converting fuel into heat.

The higher the SEDBUK rating, the more efficient the boiler is. This is not just good for our wallets, but it’s also better for the environment. Modern boilers tend to be more efficient due to improved technology and design; it’s worth looking out for models with an ‘A’ rating, as these are the most energy efficient. Installing an A-rated boiler can significantly reduce our carbon footprint and save us money on energy bills.

Here’s a quick rundown of SEDBUK ratings:

  • A-rated: 90% and above
  • B-rated: 86-90%
  • C-rated: 82-86%

To make it easier to understand how efficiency impacts our finances, we’ve compiled the following table that outlines potential annual savings for upgrading to an A-rated boiler compared to older, less efficient models:


Old Boiler Rating Estimated Annual Savings (GBP)
G (Below 70%) Up to 315
F (70-74%) Up to 220
E (74-78%) Up to 150
D (78-82%) Up to 105


The initial cost of a boiler may be higher if it has a better efficiency rating, but the long-term savings we can enjoy on our heating bills can be substantial. As such, it’s one of the most important considerations in choosing the best replacement boiler. Alongside energy efficiency, we must also weigh factors like size and compatibility to find the perfect balance for our home’s needs.


Size and Capacity Of A Replacement Boiler


When on the hunt for a new boiler, one of the key considerations we have to make is regarding the size and capacity that’ll suit our home’s needs. The boiler size isn’t about the physical dimensions – though they do matter for installation – it’s about the output capacity, measured in kilowatts (kW). This crucial aspect determines how well the boiler can heat our home and supply hot water without wasting energy.

Choosing a boiler with the correct output capacity ensures optimal performance and avoids unnecessary strain on the unit. It’ll also prevent any unwelcome surprises when the energy bill arrives. Here’s what we need to keep in mind:

  • Small apartments with up to 10 radiators and one bathroom typically need a boiler with a capacity of around 24 to 27 kW.
  • Medium-sized homes with 3-4 bedrooms, up to 15 radiators, and 1-2 bathrooms might require a boiler ranging from 28 to 34 kW.
  • Larger properties with multiple bathrooms and upwards of 20 radiators could be looking at boilers that start at 35 kW and go higher.


Home Size Radiators Bathrooms Boiler Capacity (kW)
Small Apartment Up to 10 1 24-27
Medium House Up to 15 1-2 28-34
Large Property 20+ 2+ 35+


It’s important to consult with a certified heating engineer who can carry out a heat loss calculation. This helps determine the exact kW capacity needed for our home, factoring in insulation, window sizes, and other variables that could affect heating requirements. Additionally, if we’re planning any future home extensions or significant lifestyle changes, we should factor these into our capacity calculations to ensure our new boiler can handle the anticipated demands.


How Do I Get A New Boiler Installation?


When it comes to boiler installation, it’s crucial not to cut corners. Proper boiler installation is the foundation for a boiler’s efficient and safe operation. We recommend hiring a Gas Safe registered engineer to ensure compliance with all safety regulations and manufacturer guidelines. They’ll assess the home’s layout, existing system, and your specific requirements to provide a seamless installation experience.

The installation process involves several steps:

  • Removal of your old boiler
  • Fitting of the new boiler
  • Connecting to existing pipes and radiators
  • System testing to ensure everything is working correctly

Remember, the complexity of the installation will vary depending on the type of boiler you choose and the current state of your central heating system.


How Important Is Boiler Maintenance?


Boiler maintenance is equally important and cannot be overlooked. Regular servicing not only extends the life of your boiler but also ensures it runs at peak efficiency. A well-maintained boiler is less likely to breakdown and can save you from costly emergency repairs. Here are key maintenance tips:

  • Schedule an annual boiler service with a certified professional
  • Check for leaks and drips regularly
  • Bleed radiators to remove air pockets
  • Monitor boiler pressure

By adhering to a robust installation and maintenance schedule, we not only safeguard our investment but also maintain optimal energy efficiency.




Choosing the right replacement boiler is a significant decision that can impact both our comfort and our wallet. By prioritising an A-rated boiler and consulting with certified experts for installation and maintenance, you’ll be investing in a system that not only heats your home effectively but also offers long-term savings.


Frequently Asked Questions About Boiler Types


What Should I Consider When Choosing a Replacement Boiler?

Consider energy efficiency ratings like the SEDBUK scale, the boiler’s size and compatibility with your home, and the capacity needed for heating and hot water requirements. It’s also essential to think about long-term savings over the initial cost.

How Do Efficiency Ratings Like SEDBUK Affect My Choice Of Boiler?

The Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK) rating measures a boiler’s energy efficiency. Choosing a boiler with a high SEDBUK rating (A-rated) can lead to significant annual savings on your heating bills.

Can Upgrading To An A-rated Boiler Save Money In The Long Term?

Yes, upgrading to an A-rated boiler can offer substantial long-term savings on your heating bills, despite the higher initial cost compared to less efficient models.

How Do I Determine the Correct Size Boiler For My Home?

The correct size depends on the number of radiators and bathrooms in your home. Consult with a certified heating engineer to determine the appropriate kW capacity, taking into account factors like insulation and potential home changes.

Why Is Proper Boiler Installation And Maintenance Important?

Proper installation by a Gas Safe registered engineer and annual maintenance ensure your boiler runs efficiently, prevents breakdowns, and extends its life, thereby safeguarding your investment. Regular checks like monitoring boiler pressure and bleeding radiators are also crucial.

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