If you choose the wrong shower arm for your new rain shower head, you might not get the showering experience you desire. A large rain shower head typically won't work with your existing shower arm. The shower head will be too low when installed to the existing arm. Replace the old shower arm with an arm that elevates the rain shower head to give you more showering clearance. Shower arms screw in and out of the plumbing in your wall.
Measure from the hole in your shower wall, where the shower arm is installed, to the ceiling of the shower with a tape measure. Use this measurement to know how much clearance you have to work with. Go to your local home improvement store and find a shower arm that will fit into this clearance area. You may have to measure several of them before finding one that works.
Wrap a dish towel around the existing shower arm and then grip it with a pipe wrench. Turn the handle of the wrench counterclockwise to loosen the shower arm. Untwist it the rest of the way with your fingertips. The old shower arm and shower head will come off as one piece.
Wrap the threads of both ends of the new shower arm with plumbing tape. Twist the wall end of the shower arm into the plumbing inside the wall. Turn the shower arm clockwise to accomplish this. Use your fingers until it gets difficult and then tighten it the rest of the way with the pipe wrench. Cover the shower arm with the dish towel to protect it from scratches. Tighten the shower arm until the shower side of the arm is pointing into the centre of the shower.
Screw the nut of the new rain shower head onto the new shower arm with your fingers. Place the dish towel over the nut and tighten it down with the pipe wrench. Hold the shower arm with your free hand to ensure you don't move the arm when tightening the nut.
Turn the house's water main off before executing this task.
Over tightening the shower arm or shower head can strip the threads and cut the gasket seal inside the shower head. This will cause leakage.