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Hydronic Liquid Under Floor Heating

 
   

Hydronic (liquid) floor heating are by far the most popular and competitive radiant heating system.

Hydronic floor heating is based on hot water pumped from a boiler through tubing underneath the floor; the hot water heats the slab, and the thermal mass of the slab holds the heat and drives it slowly into the house rooms.


Advantages of Radiant Liquid heating

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.


Comfort

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.


Energy savings

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.


Disadvantages of the radiant hot water floor heating

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.


Radiant wet heating floor installation
Wet installations
Image source:
Radiant Panel Association


The so-called "wet" radiant floor installations are based on tubing embedded in a thick concrete slab or in a layer of concrete, gypsum or other material installed on top of a sub-floor.

Concrete slab systems have an excellent heat capacity and combine greatly with solar energy systems.


Radiant dry heating floor installation

Dry
installations
Image source: Radiant Panel Association

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).

Tubing may also be installed from above the floor between layers of sub-floor, with tubing fitted into aluminum diffusers (to spread the water's heat across the floor).

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)…


PEX Tubing

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.


Design

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

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.


Zoning the radiant floor heating system & controls

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).


Temperatures, thermostats and controls

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.

For more information, see:
Basics on Radiant Heating Systems
Radiant Panels Heating
Radiant electric floor heating
Radiant heating floor coverings: ceramic, wood...
Radiant Systems Prices and Costs
Radiant Heating Systems and Environment


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