If you have a large home and high hot water demands, system boilers can be the ideal solution. If you are not familiar with this type of boiler you will want to know more before looking at system boiler packages and system boiler prices. Here we explain how they work, how they differ from condensing combi boilers and conventional boilers, size considerations and cost.

How does a system boiler work?

The majority of the components required for generating heating and hot water are built into a system boiler. The only external part is the system boiler cylinder that stores the hot water.

Receiving water directly from the mains, system boilers eliminate the need for a water tank in the loft (which conventional boilers require). They then heat the water for the central heating and for the system boiler cylinder.

What is the difference between system boilers and combi boilers?

The main difference is that system boilers deliver a greater volume of hot water as it keeps a store of hot water on standby in a storage cylinder. Compact combi boilers do not have a hot water cylinder because they delivers hot water on demand, rather than storing it up. This means that combi boilers are unable to meet higher demands for hot water and, therefore, properties with multiple bathrooms are better served by a system boiler.

What is the difference between system boilers and conventional boilers?

Although both conventional and system boilers are ideal for multi-bathroom properties with high hot water demands, there are fundamental differences between them. Firstly, system boilers take up less space. Unlike conventional boilers which require a feed and expansion system in the loft, system boilers incorporate an expansion vessel along with a circulation pump and valves instead. This not only eliminates the need for bulky tanks in the roof space but, by having more components built into the boiler, they are easier to install.

Secondly, system boilers deliver higher water pressure as they have the advantage of receiving water directly from the mains which is fed into a sealed system. Conventional boilers rely on a storage tank and so – without additional pumps – water pressure tends to be very low. There are situations where this is desirable such as in areas with low water pressure or homes with older radiator systems that would be unsuitable for the higher pressure of a system boiler.

In addition, due to the complexity of the pipework needed to install a conventional boiler, they are usually only recommended as part of a like-for-like boiler replacement. So, if you’re looking for a more straightforward heating system capable of meeting high demand, a system boiler will be ideal.

However, it is also worth considering that using a system boiler with an unvented cylinder can provide good hot water delivery but comes with its own special installation requirements so you should always seek advice from a Gas Safe registered engineer before choosing this option. However, if you have sufficient space and can meet the installation requirements, it could be the perfect solution.

What size system boiler is right for me?

Measured in kilowatts or ‘kW’, boiler sizes or ‘outputs’ are ratings which will tell you how much power a boiler can provide to your heating and hot water system.

It is important to avoid getting an over-sized boiler as it may be too powerful and lead to performance issues and wasted energy. Similarly, one that is too small may not heat your home properly.

Alpha also have a solution for very large domestic projects with multiple bathrooms thanks to its range of high efficiency condensing ProTec Plus system boilers. Offering 50kW system boilers right up to 115kW models, ProTec Plus boilers are ideal for central heating systems that require large outputs and they can be wall hung or fixed to a free-standing frame.


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