What Is a Combi Boiler and How Do They Work?
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A combi boiler combines your hot water and heating into one, giving you instantaneous hot water. Combination boilers cost from €2,000, and due to their high efficiency, can help you reduce your home heating bills. Combination boilers that run on fossil fuels such as gas or oil will be phased out by 2025 and are no longer permitted to be installed as part of new builds in Ireland.
What Is a Combi Boiler?
A combi boiler (also known as a combination boiler or condensing boilers) provides both hot water and heating from one single unit. A combi boiler is linked to your mains water supply and the water is heated as it passes through the boiler. This allows you to have hot water as soon as you turn on the tap (or in about 20 seconds).
Combi boilers are popular for small to medium-sized homes as they can meet the heating demands and don’t require large hot water cylinders and tanks. Models are available for gas and oil fired systems, as well as for electricity and LPG but not biomass boilers:
- Natural Gas Combi Boiler
These are the most popular combi boilers in Ireland. Since natural gas is cheaper than electricity, oil and LPG, the running costs are lower. To have a natural gas combi boiler installed, and serviced, you should consult an RGI Registered Installer. - Oil Combi Boiler
While they do exist, oil combi boilers are not very common in Ireland. They cost around 40% more than gas combi boilers to install. The running costs are also more expensive. For an oil boiler installation for your home heating, you should always consult an OFTEC Registered Installer. - Electric Combi Boiler
Electric combi boilers use an electrical element to heat water. While these are popular for homes that don’t have access to natural gas, oil or LPG, the running costs are significantly more expensive. These boilers are only suitable for homes with limited hot water needs and would require switching to a cheaper provider to be economical. - LPG Combi Boiler
For homes not connected to the gas mains, LPG may be the best choice. LPG is more expensive than natural gas, but it’s still cheaper than electricity. LPG is available to purchase in both bottled supply and bulk storage. For installations, you should consult an RGI Registered Installer.
How Much Does a Combi Boiler Cost?
The average combi boiler in Ireland costs between €2,000 and €3,000. The price you will pay for a combi boiler depends on the following various factors:
- The brand and model of combi boiler
- The type of boiler you’re replacing
- Your location
- What floor the boiler will be on
- If you want to move your boiler to a new location
- Any extras you would like to have (such as smart features)
In the following table, we have compiled some quotes for popular models of combi boilers.
| Combi Boiler Model | Price |
|---|---|
| Worcester Bosch 4000 15kW* | From €2,640 |
| Ideal Logic 18kW* | From €2,640 |
| Potterton Profile 18kW | From €2,390 |
| BAXI 600 System 18kW | From €2,490 |
Sources: Gasworks.ie*
Last Updated: September 2024
You should contact a plumber or engineer to advise you on the best option for your specific circumstances. You can also enquire to some energy providers who also offer boiler related services. For example, have a look at the Bord Gais boiler services, or contact Energia Ireland for further details.
Are There Boiler Grants in Ireland? Unfortunately, there are no longer boiler grants available in Ireland. The government is also planning on phasing out gas and oil boilers by 2025. However, there are grants available from the SEAI for heat pumps and solar water heaters.
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How Does a Combi Boiler Installation Work?
Let’s have a look at some frequently asked questions people have regarding combi boiler installations.
Can I Install My Own Combi Boiler?
The person required to carry out the combi boiler installation depends on the type of boiler.
- Gas combi boiler
A Registered Gas Installer (RGI) will need to carry out the gas combi boiler installation. - LPG combi boiler
As with a gas combi boiler, a Registered Gas Installer (RGI) will need to install the LPG combi boiler. - Oil combi boiler
An Oil Firing Technical Association (OFTEC) engineer will need to install the oil combi boiler. - Electric combi boiler
You can install the electric boiler yourself. However, it’s best to hire someone who has plumbing experience to carry out the work for you. With an electric combi boiler, an electrician will need to complete the final wiring.
Where Should a Combi Boiler Be Installed?
Even though many companies are releasing more aesthetically pleasing boilers, most individuals still prefer to have them hidden away in their homes. The top locations to have a boiler installed include the following:
- Utility room
- Kitchen
- Loft
- Bathroom
- Bedroom
- Garage
- Cupboard
Can A Combi Boiler Produce Carbon Monoxide?
As combi boilers burn fossil fuels such as gas and oil to produce heat, there is a risk of carbon monoxide poisoning if they are not taken care of with regular servicing.
What Is the Most Efficient Way To Run a Combi Boiler?
Even if you have the most efficient combi boiler, you will still need to use it in a certain way in order for it to run at maximum efficiency. You should not keep the central heating on all the time. It’s more efficient to set the heating to come on only when you need it.
The domestic hot water, however, can be left on all the time as the combi boiler only provides hot water on demand. It can take up to 20 seconds for the water to actually get hot once you turn it on.
It’s recommended to set the temperature to 75°C for central heating and to 60°C for domestic hot water.
What Temperature Should the Hot Water Be on a Combi Boiler?
Combi boilers have controls that allow you to set the temperature of the water. The recommended temperature for domestic hot water is 60°C. This is the temperature that kills legionella bacteria.
Since combi boilers don’t require a water tank, it’s unlikely that legionella bacteria will develop. Therefore, it is possible to set the water temperature a bit cooler if you like. For general safety, however, the recommended minimum temperature to kill bacteria is 60°C.
Can a Combi Boiler Run Two Showers?
Generally speaking, a combi boiler can provide water for two showers, but the flow rate will be poor. Since combi boilers heat hot water on demand, ensuring that you have enough hot water for two showers is also a big request.
To have enough hot water for two simultaneous showers, you will need to have a larger combi boiler installed. Here are some general measurements to help you determine which size combi boiler would be the best option for your home:
| Number of Bedrooms | Number of Radiators | Number of Bathrooms | Boiler Size |
|---|---|---|---|
| Small flats and apartments | Up to 10 | 1 | 15-18 kW |
| Three to four bedrooms | Up to 15 | 1 | 18-24 kW |
| Larger homes | Over 20 | 2 or more | 30 kW+ |
| Varies | 1-10 | 1 | 21-28 kW |
| Varies | 11-15 | 2 | 29-35 kW |
| Varies | 16-21 | 3 or more | 36 kW+ |
Sources: Combi-Boilers.net, BoilerCentral.com, and DuffyHeating.ie
Last Updated: September 2024
Selectra's Combi Boiler Tip
"Make sure to regulary bleed your boiler to ensure that it continues to operate at full efficiency. Trapped air inside the radiators will affect your heating system"
What Are the Pros and Cons of Combi Boilers?
Combination boilers are a good option for those looking to reduce the cost of their household heating bills, but are often a more involved and complex system to install and maintain.
Below you will find some of the pros and cons of combi boilers:
Advantages
- They use much less energy than gas-fired boilers as they don’t have to constantly heat a hot water tank.
- They are cheaper to run as you only heat the water you actually use.
- More compact and easier to install in smaller homes.
- You don't need to turn on the entire heating system just to have a bath or a shower.
Disadvantages
- Not suitable for larger homes as opening multiple taps lowers water pressure.
- Any breakdown or malfunction will leave you without heating and hot water.
- More complex setup, servicing and repairs needed.
- Risk of carbon monoxide poisoning.
Combi Boiler FAQs
Can a Combi Boiler Run Hot Water and Heating at the Same Time?
A combi boiler does not run both hot water and heating at the same time. The system will either transport the hot water to your radiators to heat your home, or it will transport it directly to your tap. The system will prioritise hot water requirements over room heating requirements.
How Long Do Combi Boilers Last?
Are Combi Boilers Being Phased Out?
Yes. From 2025, the installation of gas combi boilers and oil combi boilers will no longer be permitted in new builds in Ireland.
Learn More About Energy Saving Our energy guide articles contain lots of useful information on saving energy, lowering costs and having a more positive impact on the environment.
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