Designer vertical radiators typically have an equal BTU heat output to their horizontal counterparts. That means they should heat up in around the same time as other radiators.
Fortunately, most vertical radiators are renowned for their energy efficiency. Thanks to their increased surface area and height, they heat a room evenly and can therefore reduce your energy consumption over time.
Generally, vertical radiators with a more compact design will minimise heat loss more effectively. We recommend choosing a model that's proportional to the room size.