I have added a new radiator and pipework but unfortunately I have a joist that is directly below where I need a 15mm elbow to connect up to the radiator. I have used plastic speedfit piping and fittings throughout which means if I notch out the joist the notch would be too big as the plastic fittings are bulkly. I am thinking using a smaller Cuprofit pushfit copper elbow would be suitable as they are much smaller therefore I will be able to notch the joint out without risking weakening it. My question is this.....Has anyone had experience or knows that if I am able to connect 15mm speedfit piping onto a copper pushfit connections. This will then be connected to a copper pipe tp the radiator. Thanks. ps. there is no way I can drill through the joist as there is no room on the other side to fit an elbow.