There are two types of radiant systems: electric and hydronic. Electric systems consist of cables run under the floor and between joists or on slabs of concrete. Electric systems are not considered very cost-effective for entire homes because the cost of electricity is relatively expensive compared to other energy sources. Electric is used to retrofit single rooms, like bathrooms.
According to the U.S. Department of Energy, hydronic systems are "the most popular and cost-effective radiant heating systems for heating-dominated climates." Hydronic systems circulate heated water through heavy-grade plastic tubing, often from the home's hot water heater, to provide radiant heat.