Un-earthed heating systems often use a low-voltage supply which means they do not require the extra safety of an earth as they do not have a sufficiently high voltage to cause harm to people or ark, which can be a major fire risk.
A small number of mains voltage underfloor heating systems are still manufactured without an integrated earth and these include carbon films and some heating ribbons. These systems are not safe to install in wet areas, such as bathrooms, without the additional installation of an earthing grid above them as specified in section 753 of the 17th Edition wiring regulations.
Heat Mat’s view is that all electrical underfloor heating systems should be fully earthed as including an earth with a system can only make it more safe.
Heat Mat do not supply any un-earthed underfloor heating products.