A radiant system is based on the concept of radiant heat transfer in order to warm and cool a space. Typically we see the floor as the main medium for this system but it can also be incorporated into baseboards, walls and ceilings.
There are three varieties of radiant floor heat: air-heated, electric and hydronic systems. Hydronic is the most efficient of the three and is the focus of the discussion today.
A radiant floor heating system has a number of advantages over other types of heating:
- More efficient than forced air since there is no heat loss to duct work etc;
- No cold rooms at the end of a run;
- No moving air means no pollen and other allergy aggravating particulates such as dust are being pushed through the house;
- Hydronic systems use very little electricity;
- Heat source can be gas, oil or wood burning boilers as well as solar hot water systems;
- More consistent temperature throughout the building;
- Warms up the floor and furniture so you don’t experience a cold tile floor in the bathroom or a cold leather sofa that draws heat from your body;
- The warmest air tends to be where the people are.
A hydronic radiant floor system consists of a long length of flexible tubing that is placed in or under a floor in a series of loops. The tubing for each zone should be continuous so that there are no connections inside the floor that can fail. Water or glycol is then heated with a boiler or solar hot water and pumped through the tubes in order to warm the floor.
A hydronic radiant floor system can be used whether the floor is structural wood or a concrete slab. When the floor is concrete, the tubes are placed so that they will be encased inside the concrete. Concrete slabs are best for solar hot water based systems. When a concrete slab isn’t feasible then the tubing can be placed in a thin layer of lightweight concrete on top of a structural floor. A third way is to attach the tubing to the underside of the floor, though this is generally the least efficient. Lastly, some companies produce a panel system that has grooves for the tubing already in place.
The controls for the system can be a simple thermostat at the floor. Other systems keep track of the indoor and outdoor temperatures and try to maintain a constant indoor temperature. Due to thermal inertia the latter is often the most efficient since the system warms and cools itself as needed. There is no waiting for the occupant to become to hot before turning down the system.
The type of floor covering used is also a factor in radiant floor heat. Ceramic tile is a popular choice because it allows for excellent heat transfer. When using carpet the covering needs to be relatively thin otherwise the system will have to run at a higher temperature in order to compensate for the added insulation. Wood floors are also possible though laminated woods are recommended over solid wood. This is because there is likely to be less shrinking and cracking in a laminated floor versus a solid floor. Wood floors need to be glued, floating or else installed with care so as to not puncture the tubing.
Radiant floor cooling is in its infancy and generally only practical in dryer regions. This is because there is potential for moisture to accumulate on floors or underneath the floor. Just think of a cool can of soda on a humid day.
Commonly when cooling is needed a swamp cooler or separate air-conditioning system is installed. This is one of the reasons the radiant heat is more expensive. It is more efficient to make double use of the ductwork.
An alternative option is to use passive solar cooling such as a solar chimney or even a cooling tower that utilizes passive evaporative cooling. These systems not only use less, or no, energy but can also be an architectural statement. But that is an article for another day.