12V heated towel rails can be placed anywhere in the bathroom, including in the shower area (i.e. the opposite wall of an open-ended shower), providing the transformer and any timers/switches are placed in the correct location according to the IP rating.
A 240Volt heated towel rail can only go in certain zones of the bathroom, which is determined by the IP rating of the towel rail.
*Please note we always recommend checking the product and product specs with your electrition/plumber/builder to ensure the product will work in your space.