Will Scholfield, Engineer
31 Jan : Updated 24 Nov ● 9 min read
Choosing the perfect boiler for you and your home can be a bit of a headache. We don't really think about our boilers until something goes wrong - they're mainly just an expensive white box stuck on your wall that keeps our homes warm.
If you're currently looking for a new boiler or have recently had a new boiler system installed, you'll know how confusing it can be.
Reliable, efficient, and reasonably priced - that perfect boiler is out there. But what's the difference between a combi and a system boiler, and which one should you choose?
Here at BOXT, we’re always looking for new ways to make your life stress-free. That’s why we’ve made this helpful guide - so you can get to grips with the different types of boilers and which would be most suitable for your home.
A combi boiler (short for combination boiler) means you receive hot water and heating instantly to your home from a single unit. This means that additional tanks or cylinders aren’t unnecessary. Due to its versatility and simplicity, combi boilers are the most common boiler you'll find in British homes.
One of the main benefits of a combi boiler is its size. A combination boiler's compact size and simplicity make it ideal for most homes. This means the boiler can be fitted to almost anywhere in your home - from a cupboard in the kitchen to a wall.
Rated ‘A’ for efficiency, combi boilers only heat water when you need it. This differs from standard boilers, which heat up and store hot water in separate tanks. Combi boilers are much more efficient because they waste less energy. A more efficient boiler means less energy is being wasted, meaning you’ll save money every month when the heating bills come in.
Generally, a combi boiler is going to be cheaper to install, maintain, service, and repair than most standard or system boilers. However, if you are converting your system from a standard or system boiler, the initial conversion cost could be higher.
This is because combi boilers only have one unit generating heat, so there are no additional cylinders or storage tanks to worry about. Upgrading to an A-rated combi boiler from another type of boiler system can also save you money in the long run as they're more efficient to run and cheaper to maintain.
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Sometimes known as a conventional boiler, a standard boiler uses cold water tanks to store water that fills the system. There is also an additional hot water storage cylinder that provides hot water to your taps, outlets and radiators.
Typically, the cold water tanks will be positioned in the roof space or a loft, while the hot water cylinder will be positioned in an airing cupboard.
One downside of a standard boiler is that you only have as much hot water as can be stored in the storage tank - meaning you could run out of hot water at any time.
Standard boiler systems are normally found in larger or older homes due to the space they require to keep the separate tanks. Cold water storage tanks will usually be found in the loft, so the cold water can fall into the hot water tank on the floor below.
Due to how they work, modern standard boilers are of a similar size to combi and system boilers, but more room is taken up because of the required tanks and hot water cylinders.
However, they can meet higher demands for water. The ability to store a large amount of hot water in the cylinder means that multiple bathrooms/hot water outlets can be serviced at any one time.
Standard boilers are not as energy efficient as combi boilers, especially if it's an older model. The standard boiler's usefulness in larger homes means they are still produced, and many newer models are very efficient - over 90% in some cases.
It's worth noting that with a standard boiler, there will be higher installation and maintenance costs due to the additional tanks/cylinders and controls. This is a difference between standard and combi boilers, where everything is contained within one unit.
Like a standard boiler, a system boiler is usually used in larger homes that have a greater demand for hot water and heating. A system boiler is slightly different in that they are normally filled directly from the cold water main and are connected to a sealed system, so there is no need for feed or expansion tanks in the loft.
They are often connected to unvented hot water cylinders, which provide better hot water performance at multiple taps and showers simultaneously. They also have a central heating pump and additional controls fitted inside the boiler.
The actual boiler unit is of a similar size to both standard and combi boilers; however, you would still need room for a hot water storage cylinder of some description.
As explained above, there would be no need for the additional feed and expansion water tanks in the loft as they are fed from the cold water main and are fitted to a sealed system.
New system boilers are just as efficient as combi's in the 90% range; however, you wouldn't be heating the water instantaneously, so you would be heating a store of hot water, which could cost slightly more money.
In comparison with a combi boiler, a system boiler is more expensive to have installed, but they are much more powerful. A system boiler could be more cost-effective to run than a standard boiler, depending on usage, and there is no need for feed and expansion water tanks to be fitted in your loft.
Fitted behind electric or gas fireplaces, back boilers provide both central heating and hot water to a property. Even though this type of boiler was popular back in the 1960s, newer technologies have since come to market and pushed back boilers into taking a back seat.
Beyond falling out of favour due to the introduction of more efficient models, it's actually illegal to install a new back boiler in a UK property. This has been the case since 2005, when revised building regulations began stating that only high-efficiency condensing boilers could be installed.
If your home's central heating and hot water still run using a back boiler, we strongly recommend that you explore upgrading to a newer model.
The boiler itself is a large unit that is located within your chimney breast with a fire attached to the front of it. With this boiler, you would also need feed and expansion water tanks in the loft and a hot water cylinder somewhere within your property.
Compared to other boilers, back boilers are not efficient. In fact, the installation of non-condensing back boilers was banned in 2005 due to the high carbon emissions and Government safety regulations. Back boilers are only around 80% efficient, so for every pound you spend on heating your home, you lose 20p up your chimney!
Back boilers are incredibly expensive to run. Because they're outdated, many parts are difficult to find - meaning repairs to back boilers can be costly. They are also more expensive to service annually than the boilers previously discussed.
It is recommended that back boilers be replaced with a more economical condensing appliance.
Pros and cons of boiler types: Combi, standard and system
|Very efficient (+90% on A-rated models)||Rely on good mains water pressure in your area|
|Simple, compact design||Don't have an immersion heater|
|Easy to install||Don't work with power showers|
|No need for an additional cold or hot water tank||Not ideal for homes with multiple bathrooms|
|Compatible with solar panel systems||Can't provide hot water to multiple outlets at once|
|Work well with lower mains water pressure||Require space to install an additional storage tank|
|Provide hot water to multiple outlets simultaneously||Less efficient than combi boilers (energy is wasted during the hot water storage process)|
|Has an immersion heater as a backup source||Hot water isn't supplied on-demand (you have to heat it up in advance)|
|Good for larger homes with greater hot water demands||Can experience lower hot water pressure from taps|
|Compatible with solar panel systems|
|Able to handle high hot water demands||Water heating can be slow|
|Provide hot water to multiple outlets simultaneously||Take up more space than combi boilers (need an additional cylinder)|
|Good water pressure (connected to mains supply)||Installation can cost more than combi boilers (there are more parts involved)|
|Don't take up additional attic space (as standard boilers do)||The amount of usable hot water you get depends on the cylinder size|
|Compatible with solar panel systems|
It’s cool, we get it; choosing a new boiler for your home isn’t going to be the most exciting purchase you make this year. That being said, it might just be the most important one, so it’s worthwhile spending some time evaluating your options before selecting the model that’s right for you.
All boilers differ in price. This is why when it comes to selecting your boiler, doing a little bit of research is a good idea, as it will help you to find the brand and type of boiler that best suits your home’s needs and your financial situation.
The combi boiler has become the most popular in the UK due to its superior efficiency and compact size, but it really depends on the size of your home and budget. If you live in a larger home that demands more water, system boilers are a much more appropriate option.
At BOXT, we offer premium quality boilers from industry-leading brands like Worcester Bosch, Baxi, Ideal and Navien. Use our online Find a Boiler tool to get free, fixed-price quotes for A-rated boilers in less time than it takes to make a cuppa (go on, test us, we dare you)!