Fitting a New Radiator

Summary: Instruction and advice on fitting a new radiator. How to decide on a new radiator's size and position.

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If you want to add in a radiator to your central heating system, it’s easy enough to do. You can add a radiator at any point in the flow and return circuit, but you must make sure you don’t take heat away from the current radiators.

Position and Size

You need to work out the best position for your new radiator, and the size of radiator you’ll need. You can use an online BTU calculator to work out the size of radiator you need according to the type and size of room where you are installing it. Check the output of your boiler to ensure it can handle the extra strain of another radiator being added on.

Radiators are often installed underneath windows, because the warm air from the radiator meets the cool air from the window, and is carried around the room. However you may have one part of the room which feels colder, or the position may be dictated by furniture arrangements.

3-Column radiator

3-Column radiator

Once you have decided where the radiator is going, you need to work out the easiest way to connect it into the system. Find a nearby radiator and work out from that where the pipe run goes. Hopefully, the nearest pipes will be under floorboards, in a boxed pipe run or along the wall. If the pipes are embedded in a screed floor or under a tiled floor, you need to decide if you want to try and dig up an area of the floor (without damaging the pipes!), or can you access the flow and return from upstairs and bring the pipes down the wall?

You can identify the flow and return pipes by feeling the pipes when the heating first comes on – the pipe to heat up first is the flow pipe, and the one that stays cool for a while is the return. It is a good idea to mark the pipes so that you know which is which, as it may affect the way the valve works. If you are using a thermostatic valve, follow the instructions to make sure it is set correctly and connect it to the feed pipe.

Fitting a Radiator

Before you start, you need to drain the system – see our project draining a central heating system for help with this.

Fit the valves onto the radiator before you start so that you can see where the pipes need to come to – wrap about five turns of PTFE tape around the thread before screwing them in. Use a radiator valve key or spanner to fit the valves in nice and tightly. You may need to fit the valve adapters into the bottom of the radiator before you can attach the valves themselves. For the valves, you should have a lockshield valve at one side, and a wheelhead or thermostatic valve at the other side.

Once you have the valves in place, you can select the best exact place to position your radiator – avoiding joists etc if possible. It will make life easier for you if you don’t need to bend the pipes. Mark out where the brackets need fixing to the wall – some radiators come with a template that you can hold against the wall, but if not you can lay the radiator on its front, slot the brackets into the holders, and measure where they need to go. Make sure you allow for about 125mm (5”) clearance between the bottom of the radiator and the floor.

Fit your radiator to the wall, then get started on the pipe run. Set up your pipes to go from the radiator to where it joins the main flow and return. You can use either modern push-fit pipe or traditional copper pipe with Yorkshire fittings that are pre-soldered. If you are soldering, make sure you use a heat-proof mat to protect other pipes and woodwork around the area where you are soldering. See our project on soldered pipe joints if you need help with this.

Once you have your new pipe runs together, you need to connect them into the main feed and returns by adding in a T. Use a pipe cutter to cut a small section out of the main pipes, and fit a T connection in. If you have plastic pipes, make sure you put inserts into the ends before connecting the T, so that the pipe stays firm and keeps the joint secure.

Join your new pipe run to the radiator valves, and make sure the top blank and bleed valves are in place. You can now refill the central heating system and bleed the radiator. You may wish to add in a central heating protector at this point to help prevent limescale and corrosion in the system. Make sure all of your joints are secure and not leaking, then replace any flooring etc and enjoy your cosy room!

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