Shower heads are attached via the shower arm to a brass fitting. The shower arm screws into the brass fitting, which is screwed to a horizontal wall stud. A copper pipe runs from the inlet on the bottom of the brass fitting down to the outlet on the top of the shower mixer valve. This mixer valve has hot and cold water supply pipes entering into its bottom, and is manipulated with either a dial or hot/cold knobs to control water warmth. The copper pipe between the mixer valve and shower head brass fitting must be soldered into place.
Screw the shower head brass fitting to the horizontal wall stud. The height of the brass fitting is usually 6 inches above the top of the shower wall. It should also be equidistant between the hot/cold knobs on the shower mixer valve. The brass fitting should be installed with 1 5/8-inch galvanised screws and a drill gun.
Measure the distance between the top of the mixer valve and the bottom of the shower head brass fitting, using a tape measure. Add to this measurement the amount that the pipe will enter into the inlet on the bottom of the brass fitting, and the outlet on the top of the mixer valve--usually 1/2 inch each. Cut a new piece of copper pipe to this length with a pipe cutter.
Sand the ends of the new pipe, using emery cloth. Sand also the outlet on the top of the mixer valve and the inlet on the bottom of the brass fitting.
Smear a thin layer of flux (soldering paste) to all sanded areas, using a small brush.
Push the pipe between the outlet on the mixer valve and the inlet on the brass fitting. Uncoil 8 inches of solder from its roll. Turn on the propane torch.
Heat the brass fixture inlet by moving the flame from side to side. When the flux sizzles, remove the flame. Touch the seam between the copper pipe and inlet with the tip of the solder. if it melts, apply 3/4 inch of solder to the seam. Carefully wipe away any excess solder with an old rag. Solder the mixer valve outlet to the copper pipe, following the same steps.
Be aware of flammable objects close by when soldering. Keep a water spray bottle close at hand, in case of fires.