I take it you mean the smaller the better - as there's lack of space to fit a radiator ?
The smaller the better - is no good if it's not going to heat the space where you install it. If it's in a kitchen where finding space to fit a radiator is normally an isuue - I would personally go for a plinth/kickboard heater.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!