there are heaps of ladder-shaped ones but these result in towels flopping over each other. IMO a very wide one fits more towels; or even an ordinary rail fixed to the wall above a long low radiator.
There are two problems with the rails - most of them are chromed steel tube, and tend to go rusty. A metallurgist would know why. You may be able to get a traditional chromed brass one, the cost will surprise you.
- unless very big, they output far less heat than radiators; even less when engulfed in a thick insulating layer of towels. You may need a radiator as well as the rail.
The other thing that you need to check is how much heat they generate relative to your existing radiator. Normally they generate significantly less. If you aren't careful you may end up with a cold bathroom...
Our plumber said of towel radiators: buy the biggest you can fit in the space. Ours is six feet high, I tend to fold towels into quarters lengthways (so they are narrow) then hang at different levels. Assuming you aren't actually dunking them in the bath so they're dripping wet, they soon dry off.
Regarding the heat: I read on another thread about how they all have 'BTU' ratings and there are online calculators you can use to work out the minimum BTU you need for the room (takes into account things like the room size, windows, type of floor, etc).
Thanks everyone, I've been looking at radiators all day <exciting> and have decided I'm still going to go with one of these vintage style ones but one with a high BTU. I'll then get a nice chrome rail to attach to the wall to put the bath towels over, they dry on the bannister now so I guess they should dry on a rail.