Choosing the right boiler for your home is one of the most important decisions you’ll make when it comes to heating and hot water. But with so many types on the market — conventional, combination (combi), and system boilers — it can be overwhelming to know which one is best for your needs.
Whether you’re looking to upgrade an old system, reduce energy costs, or simply find a solution that fits your space and hot water demand, understanding the differences is key.
In this guide, we’ll break down each type of boiler, highlight their pros and cons, and help you determine which one will deliver the most efficient and cost-effective solution for your home. Let’s dive in and discover the right boiler for your needs!
Common Types of Boilers in the UK
The most popular types of boiler systems in the UK are:
- Combi boilers
- System boilers
- Conventional boilers
We’ll break down the specifications of each boiler below.
What is a Conventional Boiler?
A conventional boiler is a traditional heating system that uses a hot water cylinder and a cold water storage tank to provide both central heating and hot water. The boiler itself heats the water, which is then stored in the cylinder, allowing for a constant supply of hot water when needed.
Water is supplied to the system from the cold water tank, which feeds into the hot water cylinder. The system is ideal for homes with high hot water demand, as the cylinder can store large volumes of water for simultaneous use.
Conventional boilers can be linked to an existing tank system, making them a good option for homes with space for separate tanks. These systems are typically older and are often found in larger properties with multiple bathrooms or high water consumption needs.
Because the system relies on stored water, there is a potential for heat loss, reducing energy efficiency.
Advantages of Conventional Boiler
- Large Hot Water Supply: Conventional boilers provide a large volume of hot water, which is ideal for larger households or properties with multiple bathrooms.
- Suitable for Older Systems: A conventional boiler is often easier to install if your home already has a tank and pipe system as it integrates with the existing infrastructure.
- Reliable: The storage tank provides consistent hot water, even during times of high demand, as the water is already heated and available.
Disadvantages
- Space Requirements: Conventional boilers need both a cold water tank and a hot water cylinder, meaning they require considerable space, typically in the loft or airing cupboard.
- Heat Loss: As hot water is stored in the tank, there can be significant heat loss over time, leading to inefficiency.
- Slower Hot Water: Water must be heated in the tank before use, which can result in delays in hot water delivery, particularly during periods of high demand.
What is a System Boiler?
A system boiler is similar to a conventional boiler but with fewer components. It has a hot water cylinder for storing heated water but does not require a cold water storage tank.
This type of boiler uses mains water pressure to supply the system, and the system boiler has internal components (such as the pump and expansion vessel) built into the unit.
The water is heated directly in the boiler and then stored in the cylinder for later use, allowing for quick access to hot water. System boilers are ideal for homes with medium to high hot water demands.
The lack of a cold water tank can save space compared to a conventional system. However, the need for a hot water cylinder means some space is still required for the storage of hot water.
System boilers are often preferred in modern homes as they are easier to install and more efficient than conventional systems, offering better energy management while still providing ample hot water for multiple outlets.
Advantages of a System Boiler
- Compact Design: System boilers don’t require a cold water tank, making them more space-efficient than conventional boilers while still providing a hot water cylinder.
- Increased Efficiency: With built-in components (e.g., pump, expansion vessel), system boilers are more energy-efficient and easier to install than conventional systems.
- Reliable Hot Water: Offers an ample supply of hot water from the cylinder, making it ideal for homes with moderate to high hot water demand, especially when multiple outlets are in use.
Disadvantages
- Space for Cylinder: Although there is no cold-water tank, system boilers still require a hot water cylinder, meaning space is needed for storage.
- Limited by Tank Capacity: The supply of hot water is limited by the size of the cylinder, and once the hot water is used up, it takes time to reheat.
- Not Ideal for Smaller Homes: If your home has limited space or low water demand, the system boiler may be overkill, as it requires a storage cylinder.
What is a Combi Boiler?
A combi boiler (combination boiler) is a compact all-in-one unit that provides both central heating and hot water without the need for external storage tanks. The boiler heats water on demand directly from the main supply, which means there is no waiting time for hot water to be stored or reheated. Combi boilers are designed to be space-efficient, ideal for homes with limited space such as flats or small houses.
As the water is heated as it is needed, they avoid the energy loss typically associated with hot water storage in tanks. Combi boilers are typically installed in areas where there is limited space for traditional heating systems.
Because they do not store hot water, there is no need for a hot water cylinder or cold water tank. However, the system’s ability to provide hot water to multiple outlets at the same time is limited.
If multiple outlets are used simultaneously, the water pressure may drop. Combi boilers are most efficient in smaller homes or those with low to moderate hot water demands.
Advantages of a Combi Boiler
- Space Saving: A combi boiler doesn’t require external water tanks or cylinders, making it ideal for homes with limited space, such as flats or small houses.
- Instant Hot Water: Combi boilers heat water on demand, meaning there’s no waiting time for the water to be heated or stored.
- Energy Efficient: Since water is only heated when needed, combi boilers avoid heat loss associated with storage tanks, making them more energy-efficient than conventional systems.
Disadvantages
- Limited Water Flow: Combi boilers can only provide hot water to one outlet at a time, and using multiple taps or showers simultaneously can lead to a drop in water pressure.
- Not Ideal for Large Homes: In larger homes with multiple bathrooms or high hot water demand, a combi boiler may struggle to keep up with simultaneous water usage.
- Pressure Issues: Combi boilers rely on mains water pressure, so if the mains pressure is low, the water flow may be inadequate, impacting the performance of the system.
Factors to Consider Before Choosing a New Boiler
When choosing a new boiler for your home, there are several important factors to consider to ensure that you select the most suitable option for your heating and hot water needs.
Boilers come in different types, and each has unique advantages and limitations. Understanding these differences, along with other key considerations, can help you make an informed decision.
Here are the main factors to think about before choosing a boiler:
1. Size of Your Home and Hot Water Demand
One of the most critical factors when choosing a boiler is the size of your home and your hot water demand. Larger homes with multiple bathrooms will require a different boiler than smaller homes or flats with one bathroom.
- Combi boilers are ideal for smaller homes or flats where space is limited. They heat water on demand, meaning they don’t require storage tanks or cylinders. However, if multiple outlets (e.g., taps, showers) are used at the same time, the water pressure may drop, so they are less suitable for homes with multiple bathrooms or high hot water demands.
- System and conventional boilers are better suited for larger homes with higher hot water demand. These boilers use a hot water cylinder to store water, so they can supply hot water to multiple outlets simultaneously without a pressure drop. However, they require more space for installation, including space for the cylinder or tank.
Consider the number of bathrooms, radiators, and the frequency with which hot water is used in your household. A higher demand for hot water might require a larger system or a conventional boiler.
2. Energy Efficiency and Running Costs
Energy efficiency is another crucial factor to consider when choosing a boiler. Boilers account for a significant portion of energy consumption in the home, so selecting an energy-efficient model can help reduce your long-term running costs. Look for a boiler with a high Energy Efficiency Rating.
- Combi boilers tend to be the most energy-efficient because they heat water on demand, avoiding the heat loss associated with stored water. Since they don’t require a hot water cylinder, they are also more compact and save energy by not needing to maintain a tank of hot water.
- System boilers are more energy-efficient than conventional boilers, as they don’t have a cold water storage tank, reducing heat loss. They store hot water in a cylinder but use the main pressure for water supply, making them more efficient than conventional systems, which require both a hot and cold water tank.
- Conventional boilers, while reliable and effective, tend to be less energy-efficient due to heat loss from the hot water cylinder and the need for a cold water storage tank. However, if you have an existing system, upgrading to a more modern conventional boiler can still improve energy efficiency.
When choosing a boiler, it’s essential to balance upfront costs with potential long-term savings. Consider your household’s average energy usage and the potential savings of an energy-efficient system over time.
3. Available Space for Installation
The amount of available space in your home for installing a boiler is another key consideration. Different types of boilers have different space requirements, and the size and layout of your home will influence your decision.
- Combi boilers are the most space-saving option because they combine the boiler and hot water cylinder into a single unit. They are ideal for homes with limited space, such as flats, apartments, or smaller houses.
- System boilers require space for the hot water cylinder but don’t need a cold water tank, so they are less space-consuming than conventional boilers. They are often a good choice for homes with medium to large water demands, where space is still somewhat limited but not as constrained as in smaller properties.
- Conventional boilers require the most space since they require both a cold water tank and a hot water cylinder, which are often installed in the attic or airing cupboard. This makes conventional boilers best suited for homes with sufficient loft or cupboard space, typically larger homes with high water demand.
Be sure to assess your available space and the specific installation requirements for each boiler type. If you’re installing a new system, the space requirements for tanks and cylinders should be part of your planning process.
4. Water Pressure and Flow Rate
Water pressure and flow rate can affect how well your heating and hot water system performs. If you live in an area with low water pressure, certain boiler types may be less efficient or provide an unsatisfactory level of service.
- Combi boilers rely on mains pressure to deliver hot water. If the water pressure in your area is low, the combi boiler may not provide sufficient flow to multiple outlets simultaneously. This can result in weak water pressure, especially when running multiple taps or showers at the same time.
- System and conventional boilers are less affected by low water pressure because they can use a separate pump or rely on the tank’s pressure. However, if you have a low-pressure water supply, you may need to install an additional pump to boost pressure and ensure adequate water flow.
It’s important to check your home’s mains water pressure before selecting a boiler. If you experience low pressure, you might need to consider options that are better suited to your needs or plan for an additional pressure-boosting system.
5. Budget and Installation Costs
Your budget will be a determining factor in which boiler you choose, both in terms of the initial purchase price and the installation costs.
The upfront cost of the boiler, the installation process, and any additional components needed (such as cylinders or tanks) can vary widely depending on the type of boiler.
- Combi boilers generally have the lowest upfront cost because they are compact, require less installation work, and don’t need additional tanks or cylinders. However, they may not be suitable for larger homes or those with high water demand, so it’s important to balance cost with functionality.
- System boilers have a moderate upfront cost, which includes the cost of the boiler and the hot water cylinder. Installation is generally straightforward, especially in homes with existing system setups, but costs can rise if additional plumbing or components are required.
- Conventional boilers are typically the most expensive option, especially when you factor in the cost of installing both a cold water storage tank and a hot water cylinder. These systems also tend to have higher installation and maintenance costs due to the complexity of the system.
While the initial cost is an important factor, it’s also essential to consider long-term running costs, energy savings, and potential maintenance expenses. Be sure to obtain quotes for both the purchase and installation of each type of boiler and consider ongoing service and maintenance requirements.
6. Reliability and Manufacturer Reputation
Choosing a reliable and reputable boiler manufacturer is crucial to ensure you have a dependable system that will last for many years. High-quality boilers tend to have longer warranties, better customer service, and a stronger track record for reliability.
A Summarised Comparison of conventional, system and Combi Boiler
Here’s a summarised overview of the type of boilers;
| Boiler Type | Combi Boiler | Conventional Boiler | System Boiler |
| Space Efficiency | No external tanks are required, compact design | Requires separate cold and hot water storage tanks | Requires a hot water storage cylinder, but no cold water tank |
| Hot Water Delivery | Provides instant hot water on demand, no storage | Provides hot water in bulk, some wait time | Provides hot water quickly from the cylinder, with minimal wait |
| Ideal for | Smaller homes or flats, fewer occupants | Larger homes with high hot water demand | Medium to larger homes, moderate to high water demand |
| Energy Efficiency | More energy-efficient, heats water as needed | Less energy-efficient due to heat loss from the storage tank | More efficient than conventional boilers, but slightly less than combi boilers |
Looking to Get a Boiler for Free?
Yes, you heard that right! There are government-backed schemes that you apply to and potentially cover the complete, or partial cost of your boiler. If your boiler is older than 8 years and you are on government benefits, there is a possibility you are eligible for a free boiler replacement.
Energy Company Obligation (ECO)
The ECO scheme requires large energy companies to fund energy-saving measures in homes, especially for vulnerable and low-income households. This includes upgrading inefficient boilers, insulation, and other heating systems.
What it covers:
- The ECO scheme can provide grants or financial support to replace old, inefficient gas boilers with energy-efficient models.
- It’s aimed primarily at low-income or fuel-poor households and helps to reduce energy costs.
Which boilers are available:
Typically, the ECO scheme focuses on A-rated combi boilers and energy-efficient system boilers that help reduce energy consumption and improve overall heating efficiency.
Click here to check promptly if you are eligible for a new boiler!
Conclusion
Choosing the right boiler for your home depends on several factors, including space, hot water demand, energy efficiency, and budget.
Combi boilers are ideal for smaller homes or flats due to their compact design and on-demand hot water. System boilers offer a good balance of space efficiency and reliable hot water delivery, making them suitable for medium to large homes.
Conventional boilers, while less energy-efficient, are best for larger homes with high hot water demand, as they provide a large volume of stored hot water.
For those looking to replace old, inefficient boilers, government-backed schemes like the Energy Company Obligation (ECO) offer grants to upgrade to more energy-efficient models, or even alternate heating systems like heat pumps, potentially covering the full or partial cost.
If you’re eligible, this can significantly reduce the financial burden of upgrading to a more efficient heating system. Consider your home’s size, energy needs, and available space when selecting a boiler to ensure long-term comfort and savings.