Radiant Floor Heating Systems
Radiant heating systems provide heat directly to the floor or to panels in the walls or ceiling of a house. Radiant heating systems depend primarily on the delivery of heat directly from the hot surface to the occupants and things in the room through infrared radiation.
Radiant heating is what you feel when you feel the warmth of a hot stovetop element. When radiant heating is located in the floor, it is often called a radiant floor heating system or simply floor heating.
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Radiant floor heating systems depend heavily on the natural circulation of heat within a room, or a convection effect, caused by heat rising from the floor. Radiant floor heating systems are notably different than the radiant panels used in walls and ceilings.
There are three types of radiant floor heating systems: radiant air floor systems where air is the heat-carrying medium, electric radiant floors, and hot water radiant floors. The three types of radiant floor heating systems are further differentiated by the type of installation: wet and dry.
First are radiant floor heating systems that make use of the large thermal mass of a concrete slab floor or lightweight concrete over a wooden subfloor and the second type of radiant floor heating systems involve dry installation in which the installer "sandwiches" the radiant floor tubing between two layers of plywood or attaches the tubing under the finished floor or subfloor.
How Does it Work?
"Wet" installations are the oldest form of modern radiant floor heating systems. They work by the cables or tubing being embedded within a solid floor. The tubing or cable can be embedded in a thick concrete foundation slab or in a thin layer of concrete, gypsum, or other material installed on top of a subfloor.
If concrete is used and the new floor isn't on solid earth, additional floor support may be necessary due to the added weight. You should consult a professional HVAC engineer to determine the floor's holding capacity for this type of radiant floor heating system.
Due to recent innovations in floor technology, "dry" floors, in which the cables or tubing run in an air space beneath the floor, have been gaining in popularity for radiant floor heating systems. This is because a dry floor is faster and less expensive to build. Because dry floors involve heating an air space; however, the radiant floor heating system of this kind needs to operate at a higher temperature than wet installations.
Some dry installations of radiant floor heating systems call for suspending the tubing or cables underneath the subfloor between the joists. This method requires drilling through the floor joists in order to install the tubing. Reflective insulation must also be installed under the tubes to aim the heat in the air.
Tubing or cables can also be installed from above the floor, between two layers of subfloor. In these instances, liquid tubing is often fitted into aluminum diffusers that spread the heat of the water across the floor in order to heat the floor more evenly. The tubing and heat dispersers are secured between furring strips, which carry the weight of the new subfloor and finished floor surface.
What are its benefits (and/or drawbacks)?
A radiant floor heating system has a number of advantages: it is more efficient than baseboard heating and usually more efficient than forced-air heating because no heat is lost through ducts. It can also be advantageous because of the absence of moving air to people with severe allergies.
Liquid-based, or hydronic, systems use little electricity. The liquid-based radiant floor heating systems can also be heated with a wide assortment of heat sources, including standard gas- or oil-fired boilers, wood-fired boilers, solar water heaters, or some combination of these energy sources
A hydronic system of heating or cooling involves the transfer of heat by a circulating fluid (as water or vapor) in a closed system of pipes. A hydronic system is the most popular and cost-effective radiant floor heating system for climates that are heating-dominated.
A hydronic radiant floor system pumps heated water from a boiler through tubing laid in a pattern underneath the floor. With this type of system the temperature in each room is controlled by regulating the flow of hot water through each tubing loop. This is accomplished by a system of zoning valves or pumps and thermostats.
The cost of installing a hydronic radiant floor heating system varies by location, the size of the home, the type of installation, the floor covering, remoteness of the site, and the cost of labor.
Electric radiant floor heating systems are typically only cost-effective when there is a relatively low cost of electricity. In this case they should include a significant thermal mass, such as a thick concrete floor. Additionally, the cost of an electric radiant floor heating system is reasonable only if your electric utility company offers time-of-use rates.
Time-of-use rates allow you to heat up the concrete floor during off-peak hours. If the floor's thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to ten hours, without any further electrical input. This is true particularly when daytime temperatures are significantly warmer than nighttime temperatures.
Time-of-use applications save a considerable amount of energy dollars compared to heating at peak electric rates during the day. Electric radiant floor heating systems might also make sense if you've put an addition onto your home for which it would be impractical to extend the heating system into the addition.
Because air cannot hold large amounts of heat, air-based radiant floor heating systems are not as cost-effective in residential applications, and are seldom installed. Although they can be combined with solar air radiant floor heating systems, those systems suffer from the obvious drawback of only being available during the daytime, when heating loads are generally lower.
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