In-slab heating, whether hydronic or electric, is usually more efficient to operate than a forced-air furnace due to reduced heat loss. Since the entire floor of a home becomes a heating radiator, it requires less energy to make the rooms comfortable. However, in-slab heating can be very expensive to install.
In-slab or radiant heating uses a series of pipes embedded in floors and sometimes walls to transfer heat into a room. In a hydronic system, these pipes contain water that flows through a closed loop containing a central boiler. The boiler heats the water, and the hot water radiates heat as it flows through the pipes and tubing inside the walls. An electric in-slab system uses resistance heating, similar to the elements on an electric stove.
The most cost-effective in-slab heating option is hydronic heating, because the water maintains its heat much more effectively than heated air and it does not require the electric load that an entire electric radiant system would require. Installation costs can be steep, especially when retrofitting an older house, since flooring must be taken up in every room where the hydronic pipes are installed. This does offer an opportunity to re-insulate the floors, however, and may offer some additional efficiency savings on top of the hydronic system's benefits.