My son has asked me to help install a new radiator as I have the skills required to fit and solder the copper pipe. Radiator fitted on the wall. Boards taken up on landing, then to find the pipes running to bathroom towel rail in 15mm plastic Speedfit pipe ( this is what I intend teeing off from ) The stubs running up to the towel rail are in 15mm copper so I guess it’s changed under the floor ( can’t see that bit as it’s on the other side of joist in bathroom) I will admit I am not very well advised on Speedfit pipe , however the guy from the plumbing centre has sold us two 15mm compression tees and the Speedfit pipe inserts . I can see how these go together. Once the tees are fitted, I will then work in copper to the radiator valves. This will only require a short length of copper pipe and one elbow. What is there is there, so i can only work from that. I guess I could run it all in plastic to the TRV but I don’t think plastic pipe will look very tidy. Any advice on what I should be aware of whilst connecting compression to Speedfit would be appreciated .