Lead-based paint is usually not a hazard if it is in good consition, and it is not an impact or friction surface, like a window. It is defined by the federal government as paint with lead levels greater that or equal to 1.0 milligram per square centimeter, or more than .5% by weight.
The most common radiant floor warming systems are either hydronic (circulating hot water in tubes in the floor) or electric (heating cables in the floor). Hydronic systems are more complicated, requiring pumps and valves and modulators and so on, and, as a result, are a lot more expensive to install than electric. Still, for whole house heating solutions, hydronics are a good choice. By contrast, electric systems are inexpensive enough for single room applications and simple enough for do-it-yourselfers. Suitable for new construction or remodeling applications, electric floor warming systems include a network of cables installed in the mortar just below the tiles. These cables gently warm the tiles, operating on ordinary house current. While using a professional electrician is advised for those not comfortable working on electrical installations, these systems are generally easy to install and will not compromise the integrity of the tile installation.