Underfloor Heating
Definition:
Underfloor heating is a form of central heating which utilizes heat conduction and radiant heat for indoor climate control, rather than forced air heating which relies on convection. Heat can be provided by circulating heated water or by electric cable, mesh, or film heaters.
Underfloor heating can be used with concrete and wooden floors, with all types of floor covering (e.g., stone, tile, wood, vinyl, and carpet), and at ground level or upstairs. Choice of floor finishing requires careful consideration, because changes of floor finish may affect performance.
Advantages:
Thermal comfort
Radiant heating is arguably superior to convection methods because warm, buoyant air rises wastefully to the ceiling in convection-heated rooms, warming the upper body (often with some discomfort, particularly to the head) but leaving the lower body cooler.
In contrast, in-floor radiant heating warms the lower part of both the room and the body because when warm air convects from the radiant floor surface, it loses approximately two degrees Celsius at two meters above the floor. This imparts a feeling of natural warmth, since the limbs should ideally be warmer than the head. (The most acceptable indoor climate is one in which the floor temperature ranges between 19 and 29 °C and the air temperature at head level ranges between 20 and 24 °C.)
Humidification may still be needed for thermal comfort with a radiant system, but, for a given relative humidity, likely less humidification is needed than for forced-air heating. This is because forced-air systems, when improperly balanced (e.g., because of leaky ducts), can draw in outside air which typically has low moisture content in the winter. Asthma sufferers may benefit from underfloor heating because it reduces the airborne circulation of both dust and dust mites.
Aesthetically good
Underfloor heating is invisible from above and does not use valuable wall space with unsightly heating equipment. In a sense, the entire floor is a radiator, although, because of its area, it need not reach the high temperatures of a steam radiator. It has a particular advantage in public areas where exposed hot or sharp surfaces can be dangerous and unsightly.
Energy efficient
Air-infiltration heat loss is reduced significantly compared to forced-air systems in which imbalance due to duct leakage can drive infiltration of outside air into the building. Heating cold air from the outside requires extra energy and decreases humidity, as discussed above.
If the boiler water temperature in a hydronic system is set to the relatively low temperature required by underfloor heat, rather than the higher temperature typically used in other types of radiators, the boiler may have higher efficiency and lower standby losses. However, this is typically only possible in a boiler designed for condensing operation; in many boilers, the water temperature in the boiler must be set higher, and reduced by a mixing valve. Depending on the piping layout and insulation, there may also be lower heat losses in the water distribution system because of the lower temperature.
Although electric underfloor heating can deliver almost 100% of the electric energy coming into the building to the heated space, overall system efficiency of electric heating is low because generating electricity from heat in a power plant is less efficient than using the heat directly. In addition, whereas hydronic underfloor systems (and even forced-air systems) can be incorporated as part of an ultra-efficient geo-exchange system, electric underfloor heating does not provide for this option.
Technologies:
Modern underfloor heating systems are generally either warm water systems or electric systems. Systems can be poured into a masonry mix (called a poured floor system or a wet system) or fastened directly to the sub floor (called a sub floor system or dry system). The Roman hypocausts utilized heated air.
1.Electric Underfloor Heating , 2. Warm Water Underfloor Heating & 3. Radiant floor heating
Click to learn about hydronic heating systems
Sources:http://en.wikipedia.org/wiki/Underfloor_heating