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What is Radiant Heating?
Remember those old radiators in your elementary school? The movie Elf depicts the sounds as otherworldly in Buddy’s new NYC apartment, emitting from the large metal structure. That is radiant heating, simply. These systems supply heat directly to the floor, side panels, or ceiling of a house. Radiant heat transfer is the method of delivery from the hot surface to the people and objects in the room. This heat transfer is completed via infrared radiation. If you feel heat coming from a pan or stovetop element from across the room, that’s radiant heat. Radiant heating located within the floor is termed simply as floor heating or radiant floor heating.
Radiant heating is more efficient that baseboard heating and typically more efficient than forced air heating because duct loss is eliminated. Radiant heating is better for people with allergies because it doesn’t distribute stale air like forced-air systems can. Efficient radiant heating systems use hydronic systems (liquid-based). This uses less electricity due to the properties of water (high specific heat capacity). In areas of high electricity prices or if a home is off the grid, hydronic systems can be a great choice. Hydronic systems have a wide variety of potential energy sources to heat the liquid, including standard gas or oil-fired boilers, wood-fired boilers, solar water heaters, or some of these in combination. Check out the infographic to learn more about different energy sources and heat distribution systems for home heating. For more on the different types of energy sources and heat distribution systems for home heating, explore energy.gov’s Energy Saver 101 infographic on home heating.
Heat rises, which allows the radiant floor heating to circulate via convection. As the floor heats, the heat distributes throughout the room. Radiant floor heating systems are significantly different from the radiant panels used in walls and ceilings. Thus, the details for each are separated into different sections for your ease of reading below.
RADIANT FLOOR HEAT
Radiant floor heating comes in three types — radiant air floors (air is the heat-carrying medium), electric radiant floors, and hot water (hydronic) radiant floors. You can further categorize these types by installation. There are wet and dry installations. “Wet installations” take a large thermal mass made of a concrete slab floor or lightweight concrete over a wooden subfloor. “Dry installations” take the radiant floor tubing, sandwiching it between two layers of plywood, or attaching the tubing under the finished floor or subfloor.
Types of Radiant Heating – Floors
AIR-HEATED RADIANT FLOORS
Air does not have ideal heat retention properties. Thus, air-heated radiant floor systems are inefficient for residential property, and are rarely installed. They can combined with solar air heating systems, but suffer from the obvious drawback of only producing heat in the daytime, when heating loads are generally lower anyway. Nighttime conventional furnace inefficiency outweighs the benefits of using solar heat during the day. Although some early solar air heating systems used rocks as a heat-storage medium, this approach is not recommended (see solar air heating systems).
ELECTRIC RADIANT FLOORS
To build an electric radiant floor system, electric cables are built into the floor. Electrically conductive plastic can also be mounted on the subfloor below a floor covering such as tile.
Electricity is expensive. Thus, electric radiant floors are usually only cost-effective if they include a significant thermal mass such as a thick concrete floor and your electric utility company offers time-of-use rates. Time-of-use rates are dynamic rates, with electricity being more affordable during off-peak hours when people are sleeping (often 9pm to 6am). This allows you to charge up your radiant floor with electricity at cheaper prices. With a large enough thermal mass, the stored heat will allow eight to ten hours of comfortable house temperatures without electricity use. This is made more efficient because daytime temperatures are normally significantly warmer than nighttime temperatures. Compared to peak electric rates during the day, time-of-use rates create a significant discount.
Electric radiant floors may also make sense for home additions if it would be impractical to extend the current heating system. However, homeowners should examine other options, such as mini-split heat pumps, which operate more efficiently and also provide cooling.
HYDRONIC RADIANT FLOORS
Hydronic systems (liquid) are the most popular and cost-effective radiant heating systems for cold climates, like Minnesota or Midwest in general. Hydronic radiant floor systems pump heated water from a boiler through tubing laid in a pattern under the floor. Either zoning valves or pumps and thermostats can control the flow of hot water through each tubing loop, which regulates room temperatures. The cost of installing a hydronic radiant floor varies by location and depends on the size of the home, the type of installation, the floor covering, remoteness of the site, and the cost of labor. Please contact your local Rochester Plumbing and Heating service to receive a quote, 773-354-0342.
TYPES OF FLOOR INSTALLATIONS
Electric and hydronic floor system installations are similar.
The “wet installations” are the oldest form of installing modern radiant floor systems. These installations involve embedding the cables or tubing in a solid floor using a thick concrete foundation slab or a thin layer of material installed on top of a subfloor. Ranch style houses do not have basements, and thick concrete foundation slabs can be found commonly. If concrete is used and the new floor is not on solid earth, the added weight may require additional floor support. An engineer is critical in this process to determine the floor’s force support capacity.
Solar energy systems, due to their fluctuating heat output, generally use thick concrete slabs to retain heat. But thick slabs have a slow thermal response time. This makes strategies such as night or daytime setbacks difficult. Maintaining constant temperature is recommended in homes with these heating systems.
“Dry floors” are a recent innovation in heating technology. The cables or tubing are built into an air space beneath the floor. Dry floors can be built more quickly at a more affordable price. The drawback is higher operating temperatures, due to dry floors heating an air space.
Some dry installations involve suspending the tubing or cables under the subfloor between the joists. This method usually requires drilling through the floor joists to install the tubing. Reflective insulation must also be installed under the tubes to direct the heat upward. Tubing or cables may 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 water’s heat across the floor in order to heat the floor more evenly. The tubing and heat diffusers are secured between furring strips (sleepers), which carry the weight of the new subfloor and finished floor surface.
At least one company has improved on this idea by making a plywood subfloor material manufactured with tubing grooves and aluminum heat diffuser plates built into them. The manufacturer claims that this product makes a radiant floor system (for new construction) considerably less expensive to install and faster to react to room temperature changes. Such products also allow for the use of half as much tubing or cabling, because the heat transfer of the floor is greatly improved compared with more traditional dry or wet floors.
So which materials will heat your space most efficiently? Ceramic tile is the most effective floor covering for radiant floor heating. it both conducts heat well and adds thermal storage, making it an ideal material. Common floor coverings like vinyl and linoleum sheets, carpeting, or wood can also be used. These coverings insulate the floor from the room and decrease the efficiency of the system.
If you desire carpeting, use thin carpet with dense padding, installing as little as possible. If some rooms, but not all, will have a less efficient floor covering, then those rooms should have a separate tubing loop to make the hydronic system heat these spaces more efficiently. The added loop is necessary to increase the temperature to permeate the added floor covering. Wood flooring should be laminated wood, rather than solid wood. The drying effects of heat can cause solid wood to shrink, warp, and crack, leading to increased costs of repair.
RADIANT HEATING – PANELS
Radiant panels can be mounted on the wall or ceiling. They are usually aluminum and can be heated with either electricity or hot water tubing. The downside of hot water tubing is the concern of leakage. Most commercially available radiant panels are electrically heated.
With an electric source, radiant panels can be expensive to operate. They can be an asset by providing supplemental heating in some rooms or a home addition when extending the conventional heating system is deemed impractical.
Radiant panels have the quickest response time of any heating technology. Due to individually controlled panels, energy savings is often a result compared with other systems when rooms are infrequently occupied. The quick response feature allows a room occupant to migrate into a room, increase the temperature setting, and then be comfortable within minutes. As with any heating system, always set the thermostat to a minimum temperature that will prevent pipes from freezing in cold temperatures.
Radiant heating panels will heat most intensely close to the panel, operating on a line-of-sight basis. Some people find ceiling-mounted systems uncomfortable because the panels heat the top of their heads and shoulders more effectively than the rest of their bodies. Not only this, but ceiling-mounted heating panels are less efficient due to physical properties of heat rising. More heat required, with the result of cold feet often leaves the user dissatisfied or in need of adjunctive heating.