There are many variables (insulation, does the room have windows, does it have a outside wall).  that will determine how effective a towel warmer will be at heating a room.  Runtal is known for it's ability to help heat a room.  Amba also has several models (Quadro, Sirio, Antus, Vega) that can act as a space heater as well.   There are many BTU calculators that you can find online that will give you the suggested amount of BTU/Watts required to warm a room, but many of these assume that you are heating the room from 0 degrees. This is 99% of the time, not true. Although, it may be the main source of heat for the bathroom, it will still get some residual heat from the rest of the house, so you must determine how many degrees you want to heat the room. Please do not hesitate to contact us with any questions.