How to install central heating

Installing central heating

The below guide is specifically for a central heating system that uses a combi boiler to produce hot water. A system that requires a cold water tank in the loft and a hot water storage tank is more complicated and may take longer to install.

Before anything can be installed, your installer will need to decide on where your radiators will be located, how many you will need and what type of boiler you want, such as a combi boiler. These decisions are crucial.

You can discuss your requirements with an installer who will assess the heat loss and may make a basic drawing of your home and mark where things will be going. This includes pipework, taps and radiators. Don’t worry about it being spot on, as a heating engineer will be able to identify any issues. Remember when choosing a position for your radiators the installer may decide that these are best located under windows.

When the system is being fitted, the engineer will likely install the cold feed first, unless your home already has one. This is the pipework that brings water into your home via the mains. Generally, it will run underneath your flooring. If you have a floating floor, the pipework can be installed by cutting into the foam insulation. For a suspended floor, the pipework will need to run through the joists, meaning some may need to be cut slightly to make room for the pipes. If your floor is made of concrete, it may need to be chiseled to form a channel.

The main cold water feed will come into your home and to the stopcock, which is where you can turn the mains off should an emergency occur, such as a burst pipe. Copper piping then leads from the stopcock to the rest of the house where cold water is needed, like a tap, toilet or shower. This is why it’s so important to work out where the pipes are needed and which appliances will be going where.

Cold water taps should always be installed on the right and hot water on the left as you’re looking at where the appliance will be fitted. For instance, if you pretend you’re standing where the kitchen sink will go, the cold feed should be on the right. A cold water feed will also need to lead to the combi boiler.

As previously mentioned, in order for pipes to be installed, the flooring may need to come up so that they can be placed between the joists. The walls may also need to be drilled into so that the pipes can be channelled. The walls will then be replastered or skimmed to hide the pipework.

Once the cold water feed is in, it’s time to think about how the water that’s heated by the boiler will travel around your home. Where the boiler will eventually be installed, there should be a cold feed going from the mains into the boiler and a hot water pipe that can take the heated water around your home. Appliances such as showers and taps need both hot and cold water, however toilets only need cold.

The central heating will need a flow and a return. The flow takes hot water from the boiler and dispenses it to all the radiators in your house. Like the cold feed, the hot water pipes will be laid in the floor and the flow connections should, wherever possible enter the radiator on the left hand side. Once the hot water has been around all the radiators, going in on the left side and out through the right the water will then go back to the boiler. By this point, the water may have dropped in temperature and might need to be reheated by the boiler, ready to loop around the whole system again.

When installing central heating, a heating engineer should use the manufacturer’s instructions for appliances like the boiler. These can generally be found on the website as a PDF document but they should come with the boiler when it’s delivered.

The pipe that leads from the mains to the stopcock needs to be large enough so that your taps get a good amount of pressure - around 25 mm will do. The pipe that leads from the stopcock into the boiler can be around 22mm or 15mm depending on the distance. Elbow joints can be used when you reach a corner to direct the pipe in a different direction. These can be soldered together to ensure no water can escape through the join, some installers use plastic fittings and these will generally be pushfit.

The radiators are hung on the walls high enough to fit valves, most installers bring the pipework to the radiator. When the system is turned on for the first time, it will need to be balanced.

Can I use plastic pipe for central heating?

Plastic piping is becoming more and more common in UK homes because of its affordability. Plastic is significantly cheaper than copper, but does this mean you should use it?

Plastic piping can be used for some applications, such as the feed to a tap or even underfloor heating. It can withstand hot temperatures, making it ideal for hot water feeds, and it is easier to install thanks to the push-fit joints that replace the need for soldering copper pipes. However, plastic pipes should never be directly connected to a boiler.

Do you have to put an inhibitor into a central heating system?

Viessmann do not recommend the use of inhibitors in a sealed central heating system. Traditionally it has been thought that inhibitors would help prevent corrosion. This is not necessarily the case on sealed systems as there is no air ingress which could promote corrosion. 

Where air ingress is unavoidable, for example open vent systems then a correctly dosed inhibitor may be necessary. Always follow manufacturer instructions for guidance.

How disruptive is installing central heating?

Installing a whole new central heating system can be quite disruptive, however your installer will aim to make the task as mess free as possible by planning everything carefully. The more this is planned, the less disruption there will be. In some cases, walls and floors may need to be chased to make way for new pipework, so be prepared to do some decorating once the work is finished.