So what Gas Boiler is right for you?

Combi boiler, heat only boiler or system boiler?

We know it can be difficult to choose the right boiler.

Gas Boilers come in all sizes, both physically and in terms of output. From a combi boiler to normal types, We will guide you safely through the process of picking the right Gas boiler.

There are three types of domestic Gas boilers and they all range in outputs between 7kw – 40kw. However it’s important to note that combi boilers only start from 24 kw output. 

Most 3/4 bed homes only require a 15 kw gas boiler. It’s important not to oversize a condensing boiler for your home.

This is because it’s harder for the boiler to condense if it’s too large for the number of rads it’s supplying resulting in a less efficient system. As a result your boiler burns more gas then is required.

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Example of a HEAT ONLY type boiler in a restricted space underneath a kitchen counter. Notice the pump located at the top and the vessel at the bottom. As a result, both are fitted outside the boiler.

Are physically the smallest types of Gas boiler. They’re perfect for tight units and are also the best option for heating systems with old pipe work and radiators.

Although some system boilers can also operate low pressures.

HOWEVER, unlike modern Gas system boilers they don’t incorporate the safety valve, pump and expansion vessel resulting in longer installation times.


SYSTEM BOILER in kitchen cupboard
Example of a system boiler. With these boilers the expansion vessel and pump are built into the boiler. As a result these parts are covered under the boilers warranty.

Are slightly larger in physical size than heat only Gas boilers but incorporate the pump,vessel and safety valve resulting in a neater more uniform finish and quicker install.

This is the most common Gas boiler to be used in most Irish homes.


Cylinders in apartments take up valuable storage space
We removed the cylinder  after the installation of one of our COMBI BOILERS.
A combi boilers mains needs a delivery of at least 16 liters per minute to operate, anything below this will not suffice and a pump will need to be installed.

Look identical to system Gas boilers but incorporate a separate plate heat exchanger for hot water demands,eliminating the need for a hot water cylinder in your hot press.

HOWEVER, you will lose the backup of an immersion and with most combi Gas boilers needing a steady non fluctuating high pressure mains water supply,you will most likely need to add an expensive booster pump (depending on your hot water demands).

Also, when installing combi boilers careful consideration has to be given to the gas supply. If it’s undersized ( and more than likely will be) a new gas line will have to be ran to it to satisfy the load that combi boilers demand.

This is because when hot water is drawn the boiler goes to “high fire”. Basically the boiler gives it everything it’s got and if it’s not getting enough gas it simply won’t operate.

In some circumstances retrofitting a combi boiler can be in practical and extremely expensive. However when planned and installed properly, a combi boiler is the most practical and efficient hot water solution.


The combi layout has no Hotpress or attic Tank. This layout is entirely dependent on a strong incoming water mains. If the mains cannot provide this a booster pump must be installed. In this case the attic tank must be left to supply water to the new pump.