Types of Boiler Systems Explained (and what you’ll need for your home)




Whether you’re considering a combi or a conventional, it’s crucial that you pick the right type of boiler for your home. Here, you’ll learn about the different options and which is best suited to your home’s demands.


There are three main types of boilers you can install into your home: combi boilers, heat only (regular boilers) and system boilers.


The one most suitable for you and your home largely depends on your current hot water demands, but it is also important to consider other factors, such as the age of your current heating systems and the pressure of your mains water supply.


All modern boilers have very good lifespans and are generally easy to service and repair.




Combination (Combi Boilers): What are they?


A combi boiler provides both your heating and your hot water from a single unit, typically wall hung.




So, how do combi boilers work?


Combi boilers utilise a metallic heat exchanger to instantly heat hot water on demand, they achieve this via combustion e.g. by burning fuels such as gas or oil.




This is the biggest distinction of combi boilers, as unlike traditional boilers they do not require a separate hot water storage tank.


Instead, the hot water is heated immediately from a single unit.


Learn all about combi boilers in our what is a combi boiler guide.


Curious to know which boiler brand performed worst? Find out in our report of the worst boilers.




Pros of combi boilers


If you are looking for a boiler that’s highly energy efficient, a combi (combination) boiler might be the solution. They can be used to heat the home as well as its water, saving you a wedge on heating bills.


Their compact size makes them ideal for even the smallest of properties, and since they use the mains to heat water, you will not have to make space for a cumbersome water tank or cylinder.


Another plus is that because they can instantly heat the water you need; you will not have to wait around for that hot, sultry shower.



Cons of combi boilers


There are a few drawbacks to consider.


Water flow rates are reduced when two or more outlets are being used at the same time.


So, if you have got a larger property with a few bathrooms (which may be used at the same time), a combi might not be the right choice for you.


Ultimately, a combi boiler can only heat the water which gets fed to it from the mains. So, if your mains water pressure is low, your combi boiler won’t work very well.



Combi boiler key points:


  • The compact design makes them ideal for properties with limited space.

  • Do not need a hot water storage cylinder.

  • Do not need a cold-water tank.

  • Typically, not suitable for larger properties with multiple bathrooms/or a high hot water demand.

  • May not be suitable for areas that suffer from low mains water pressure.


 Heat Only (Regular Boilers): What are they?


A heat-only or regular boiler has three main components – the boiler itself, a separate hot water storage cylinder and cold water storage tank.


The boiler supplies hot water to both the central heating and storage cylinder, so can provide both hot water and heating water.


 How do heat only boilers work?


Regular boilers work by feeding hot water directly to the central heating system i.e. the radiators and storing hot water within a hot water storage cylinder for on-demand use.


Cold water is supplied to the boiler via a cold-watertank (typically located in the attic/loft), which fills the boiler with the help of gravity.



Pros of heat only boilers


Heat only boilers can provide a greater flow rate and as a result, are more suitable for larger properties with greater hot water demands e.g. those with multiple bathrooms.


As they do not require water to be supplied at high pressure via the mains, they are a good option for older heating systems that may not tolerate the high pressure of a closed system.


Alternatively, they are also a good choice for areas that have low water pressure mains supplies, that typically struggle to supply adequate water pressure required in combi and system boilers.


Check our new boiler costs guide and use our boiler size calculator if you want to get a better understanding of how our fixed price boiler quote tool works.



Cons of heat only boilers


A conventional boiler may not be compatible with some newer heating systems, and you might have to wait a while for the water to reach the right temperature.


Also, bear in mind that you will need somewhere roomy to store the boiler’s cylinder and water tank. Since the cold-water cistern needs to be installed directly above the boiler, this may also limit where you can install the boiler too.



Heat only boiler key points:


  • Good choice for properties with multiple bathrooms and high hot water demands.

  • Ideal for areas that suffer from low water pressure.

  • Good choice for those with older/traditional heating systems that cannot tolerate high pressure.

  • Since they require a cistern tank, they demand more space and limit boiler installation options.

  • A cistern in the attic is prone to freezing during winter and if it leaks can be problematic.




System Boilers: What are they?


System boilers are essentially an upgraded version of the regular or heat-only boiler. They can provide both hot water on demand and heating water for your radiators.



How do system boilers work?


Just like a heat-only boiler, they have a separate hot water tank, except that it is unvented.



Pros of system boilers


Just like heat only boilers, there large hot water storage cylinder means they are ideal for properties with high hot water demands.


Since they have all their components internalised and do not require a cold-water cistern, it means that they do not require as much space as a heat-only boiler. It also means there is more flexibility with the installation location.


System boilers do not require any components in the attic, it also means that you do not have to worry about any potential leaks or freezing during the winter months.



Cons of system boilers


The hot water flow rate within the home largely depends on the pressure of the mains supply, so if t’s low, the flow rate within the home will be limited. For this reason, they are not ideal for places that suffer from low water pressure.


The high-pressure nature of this system means that it may not be suitable for properties with older systems.


System boilers need a hot water storage cylinder and so if you are swapping it for a combi boiler, you will need to find adequate storage space.



System boiler key points:


  • Recommended for properties with multiple bathrooms/hot water outlets.

  • Does not require a cistern tank in the loft.

  • Internal components make installation easier.

  • May not be suitable for areas that suffer from low water pressure.

  • May not be suitable for older central heating systems that cannot tolerate high water pressures.

  • If you are swapping from a combi, you need to consider where you will store the hot water tank.




Boiler Type Frequently Asked Questions


Are you still curious about some aspect of choosing a new boiler? It’s not surprising for such a complex piece of engineering, here are some of the most frequently asked questions:



What is a condensing boiler?


No matter what type of boiler you are thinking of having installed, the law says that it must be a condensing one.


All condensing boilers are at least 90% energy efficient, can harness excess energy to heat your home, are better for the environment and will help to reduce your heating bills.


Condensing isn’t a ‘type of boiler’ as such, it’s more of a technical attribute.



What size boiler do you need?


When considering boiler size, it typically refers to the boiler’s power output and not the dimensions of the boiler. A boilers power is measured in kilowatts per hour (kWh), so put simply, the greater the kW, the greater the capacity of the boiler to meet your properties hot water and heating requirements.