Can I use DC to drive underfloor heating wire?
Some older installations around my way use steel cable (often stuff used for lifting, but now worn out) set directly into poured concrete slabs. The concrete is insulated below, and has a large heat capacity. The heating runs overnight when electricity is cheap, and the concrete stays warm through the day.

These systems are designed to be AC. Applying DC for long periods may cause galvanic corrosion at the steel-concrete join. How bad depends on the condition of the concrete when you start.  Fortunately, it's only a problem if the steel cable is positive with respect to ground, if it's negative, then it is protected instead.