Radiant heating systems supply heat directly to the floor or Â to panels in the wall or ceiling of a house. The systems depend largely on Â radiant heat transfer -- the delivery of heat directly from the hot surface to Â the people and objects in the room via infrared radiation. Radiant heating is Â the effect you feel when you can feel the warmth of a hot stovetop element from Â across the room. When radiant heating is located in the floor, it is often Â called radiant floor heating or simply floor heating.
Radiant heating has a number of advantages. It is more Â efficient than baseboard heating and usually more efficient than forced-air Â heating because it eliminates duct losses. People with allergies often prefer Â radiant heat because it doesn’t distribute allergens like forced air systems Â can. Hydronic (liquid-based) systems use little electricity, a benefit for Â homes off the power grid or in areas with high electricity prices. Hydronic Â systems can use a wide variety of energy sources to heat the liquid, including Â standard gas- or oil-fired boilers, wood-fired boilers, solar water heaters, or Â a combination of these sources.
Despite its name, radiant floor heating depends heavily on Â convection, the natural circulation of heat within a room as air warmed by the Â floor rises. Radiant floor heating systems are significantly different from the Â radiant panels used in walls and ceilings. For this reason, the following Â sections discuss radiant floor heat and radiant panels separately.
RADIANT FLOOR HEAT
There are three types of radiant floor heat -- radiant air Â floors (air is the heat-carrying medium), electric radiant floors, and hot Â water (hydronic) radiant floors. You can further categorize these types by Â installation. Those that make use of the large thermal mass of a concrete slab Â floor or lightweight concrete over a wooden subfloor are called "wet Â installations,” and those in which the installer "sandwiches" the Â radiant floor tubing between two layers of plywood or attaches the tubing under Â the finished floor or subfloor are called "dry installations."
TYPES OF RADIANT FLOOR HEAT
ELECTRIC RADIANT FLOORS
Electric radiant floors typically consist of electric cables Â built into the floor. Systems that feature mats of electrically conductive Â plastic mounted on the subfloor below a floor covering such as tile are also Â available.
Because of the relatively high cost of electricity, electric Â radiant floors are usually only cost-effective if they include a significant Â thermal mass such as a thick concrete floor and your electric utility company Â offers time-of-use rates. Time-of-use rates allow you to "charge" the Â concrete floor with heat during off-peak hours (approximately 9 p.m. to 6 Â a.m.). If the floor's thermal mass is large enough, the heat stored in it will Â keep the house comfortable for eight to ten hours without any further Â electrical input, particularly when daytime temperatures are significantly Â warmer than nighttime temperatures. This saves a considerable number of energy Â dollars compared to heating at peak electric rates during the day.
Electric radiant floors may also make sense for home Â additions if it would be impractical to extend the heating system into the new Â space. However, homeowners should examine other options, such as mini-split Â heat pumps, which operate more efficiently and have the added advantage of Â providing cooling.
HYDRONIC RADIANT FLOORS
Hydronic (liquid) systems are the most popular and Â cost-effective radiant heating systems for heating-dominated climates. Hydronic Â radiant floor systems pump heated water from a boiler through tubing laid in a Â pattern under the floor. In some systems, controlling the flow of hot water Â through each tubing loop by using zoning valves or pumps and thermostats Â regulates room temperatures. The cost of installing a hydronic radiant floor Â varies by location and depends on the size of the home, the type of Â installation, the floor covering, remoteness of the site, and the cost of Â labor.
TYPES OF FLOOR INSTALLATIONS
Whether you use cables or tubing, the methods of installing Â electric and hydronic radiant systems in floors are similar.
So-called "wet" installations embed the cables or Â tubing in a solid floor and are the oldest form of modern radiant floor Â systems. The tubing or cable can be embedded in a thick concrete foundation slab Â (commonly used in "slab" ranch houses that don't have basements) or Â in a thin layer of concrete, gypsum, or other material installed on top of a Â subfloor. If concrete is used and the new floor is not on solid earth, Â additional floor support may be necessary because of the added weight. You Â should consult a professional engineer to determine the floor's carrying Â capacity.
Thick concrete slabs are ideal for storing heat from solar Â energy systems, which have a fluctuating heat output. The downside of thick Â slabs is their slow thermal response time, which makes strategies such as night Â or daytime setbacks difficult if not impossible. Most experts recommend Â maintaining a constant temperature in homes with these heating systems.
Due to recent innovations in floor technology, so-called Â "dry" floors, in which the cables or tubing run in an air space Â beneath the floor, have been gaining in popularity, mainly because a dry floor Â is faster and less expensive to build. But because dry floors involve heating Â an air space, the radiant heating system needs to operate at a higher Â temperature.
Some dry installations involve suspending the tubing or Â cables under the subfloor between the joists. This method usually requires Â drilling through the floor joists to install the tubing. Reflective insulation Â must also be installed under the tubes to direct the heat upward. Tubing or Â cables may also be installed from above the floor, between two layers of Â subfloor. In these instances, liquid tubing is often fitted into aluminum diffusers Â that spread the water's heat across the floor in order to heat the floor more Â evenly. The tubing and heat diffusers are secured between furring strips Â (sleepers), which carry the weight of the new subfloor and finished floor Â surface.
At least one company has improved on this idea by making a Â plywood subfloor material manufactured with tubing grooves and aluminum heat Â diffuser plates built into them. The manufacturer claims that this product Â makes a radiant floor system (for new construction) considerably less expensive Â to install and faster to react to room temperature changes. Such products also Â allow for the use of half as much tubing or cabling, because the heat transfer Â of the floor is greatly improved compared with more traditional dry or wet floors.
Ceramic tile is the most common and effective floor covering Â for radiant floor heating, because it conducts heat well and adds thermal Â storage. Common floor coverings like vinyl and linoleum sheet goods, carpeting, Â or wood can also be used, but any covering that insulates the floor from the Â room will decrease the efficiency of the system.
If you want carpeting, use a thin carpet with dense padding Â and install as little carpeting as possible. If some rooms, but not all, will Â have a floor covering, then those rooms should have a separate tubing loop to Â make the system heat these spaces more efficiently. This is because the water Â flowing under the covered floor will need to be hotter to compensate for the Â floor covering. Wood flooring should be laminated wood flooring instead of Â solid wood to reduce the possibility of the wood shrinking and cracking from Â the drying effects of the heat.