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Hydronic (liquid) floor heating are by far the most popular and
competitive radiant heating system.
Radiant Liquid heating offers top comfort, extremely quiet operation, improved air quality (no dust, no eventual toxic or chemical infiltrations…), significant energy savings and is particularly suitable to work with solar water heater systems or geothermal heat pumps.
Most of all, radiant liquid floor heating means enhanced comfort. The large radiant surface (the whole floor), the nature of the heating (radiation) and the fact that floor surface is itself warm (allowing people to walk around barefoot) explain that enhanced comfort.
The delivery of heat at floor level and the absence of significant airflow allow comfort at relatively low thermostat temperatures (70°F / 20°C). Relatively to forced-air heat, radiant-floor systems do not increase the rate of air infiltration, which is also a source of energy savings.
The relatively high cost and the long lag-time between the activation of the radiant floor system and the heating of the rooms of the house are the main disadvantages of the system.
Concrete slab systems have an excellent heat capacity and
combine greatly with solar energy systems. Radiant floor “dry" installations are relatively new approaches in which the tubing runs in an air space under the floor.
Some installations involve suspending the tubing
under the sub-floor between the joists and require reflective
insulation under the tubes (in order to direct the heat upward).
PS: Dry radiant floor heating needs to operate at
a higher temperature and demands more energy than “wet” systems,
but some manufacturers are presenting cheaper “dry” packages
with faster response times and less tubing (or cabling)… Cross-linked polyethylene (PEX) tubing is a very common solution today for tubing. Rubber tubing is also used, though in a much smaller scale. Copper piping is a solution of the past.
Radiant floor design can be rather complex. The length of tubing per square foot of floor depends on many variables: climate, tubing diameter, radiant-floor system, type of boiler and controls… Some manufacturers present packages integrating the various components, which simplifies the design of radiant-floor systems.
Insulation beneath the tubing or the heated slab is crucial for radiant-floor heating systems performance. Minimums of 1”/25 mm of extruded polystyrene are often applied, but these levels should be higher in the coldest climates.
The temperature in each room of the house can be controlled by regulating the temperature of the flow of water through each tubing loop – which can be accomplished by valves, pumps and thermostats. Zoning the system is important, since maintaining different temperatures in different parts of the house allows energy savings and can respond to different needs (spaces with and without solar gains, for instance).
To provide maximum comfort and to regulate where the heated water should be driven, radiant-floor systems may use temperature sensors: outdoors, in the rooms, in the floor slab... Traditional standard thermostats do not provide the necessary flexibility in that regulation. These specific controls can also be used to overcome the long lag-time of radiant-floor heating systems, since the radiant floor system can be programmatically activated in advance.
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