Radiant Floor Heating

How it Works

Radiant floor heating consists of two primary components: tubing, which is placed beneath the floor, and a heating source, a water heater or boiler. The technology that makes these systems work can be used with pretty much any hot water heat source or fuel, such as standard gas or oil-fired boilers, wood-fired boilers, solar water heaters, or a combination, but systems fueled by natural gas are the most efficient and most often used.

Most systems rely on air circulation to distribute heat; however, radiant heating exploits the physical properties of warm air, which rises, to provide comfortable warmth where installed. What is neat about these systems is they warm people and objects directly, which is the same principle as solar heating. The heat produced radiates upward and outward, which in turn spreads warmth and comfort with greater efficiency throughout the space.

Radiant floor heating can be used as either a primary or secondary system. As a secondary system, they can be beneficial in specific rooms or locations within the structure, and are used as a supplement to a primary heating system. When used as a secondary system, they are typically, but not always, added after construction. These systems can also be used as a primary system; this is more common in new construction, and is typically added throughout the home or structure during construction. There are three basic radiant floor system configurations: single purpose system, dual purpose system, and contained system.

In a single purpose system, the radiative floor is a secondary source, used to supplement a primary system. A separate water heater or boiler provides heated water for the radiant floor system as a conventional furnace or boiler and water heater simultaneously handle regular demands. In the single purpose arrangement, individual appliances perform only one function.

In a dual purpose system, a single unit performs two functions, supplying energy for both the radiant floor system and household hot water. In some instances, a boiler or conventional furnace may be installed to handle primary home heating with the radiant floor heating used as a secondary source, or for a specific location or space. Hybrid configurations are common, combining these two systems.

In a contained system, there are separate coils within a single tank that separate the supplies for the radiant floor heating system and the household drinking water. A benefit to this is when systems could potentially be exposed to cold weather in a seasonal or outdoor installation. Since the systems are completely separated, the drinking water supply can be drained or flushed, and the tubes for the heating system can be filled with glycol rather than water so they doesn’t freeze. This arrangement is not necessarily primary or secondary, but rather refers to the arrangement of the system.

Typical Uses

Radiant floor heating is typically used in homes. It works best in smaller spaces, and is typically not used in larger scale projects, such as high rises, as a primary system. Radiant floor heating can be added to existing homes as a supplemental source of heating, or can be added with new construction as a more primary heating source.

Within homes, radiant floor heating systems can be added to a number of different floor types and added to floors in different ways. They can be added as part of a concrete floor, to a suspended floor, in a poured floor underlay, and between joists. They can also be added via the track method, which is adding tubing in fixed channels between wooden slats with metal backing; this is a quick way to install this system, and is great for adding to a pre-existing structure.

Although it is most commonly used in homes, it can also be used in other small spaces that are part of a larger building as a supplement to a larger HVAC system. It would make the most sense to use a system like this in a small public space that people pass through rather than spend a large amount of time in because it is unlikely that the temperature would remain constant with circulation. In this case, the radiant floor heat would be used to warm a space that does not need to remain a specific temperature, but rather just as an in-between heating source; for example, an entryway. As people enter the building, the radiative floor would serve the purpose of warming the space, providing comfort to those entering the building. Using this example, as a part of a large building, the temperatures will fluctuate dramatically when the temperature differential outside is extreme and is then exposed to the interior conditions, so keeping the temperature constant would be difficult. However, warmth is always welcoming, especially when radiating from the floor. Another location radiant heating can be used is outdoors, beneath walkways and driveways to melt snow and ice, and in cabins or other seasonal facilities. These systems will need to be filled with non-freezing liquids, but do not need to be drained when the weather turns cold.

Numeric Parameters

There are a few parameters that must be considered when using radiant floor heating, especially when adding to an already-constructed home or structure. When adding radiant heat, one of the most common type of systems is called a thin slab system. This system either consists of a specially formulated concrete or poured gypsum underlayment, and these each have special requirements that must be accommodated for. When adding a thin-slab, it typically adds 1.25 to 1.5 inches to the floor height, which can affect door and window openings, as well as stairs. Another accommodation that much be addressed is the added weight of the thin-slab; poured gypsum thin-slabs typically add 13 to 15 PSF (at 1.5” thickness).

Because of how radiant floors work, when used as a supplemental system, the thermostat can be set several degrees lower. Heat radiates from the entire surface of the floor about the same amount of heat the human body does, heating occupants directly rather than through an indirect method (such as a forced air system). A room with radiant floor heating with 65 oF (18 oC) is typically considered a comfortable temperature. Radiant floor heating systems also do not require air from the outdoors, meaning they can operate at a lower temperature, around 85-140 oF (29-60oC), compared to other systems that operate at a range of 130-160 oF (54-71oC).

Limiataions

Radiative floor heating is limited in many parameters. It is typically only used as a heating source, and is not always used as the primary source. Depending on the expanse of the room in which the radiant heating is installed, there can be hot spots where the heat is concentrated due to cooling with flow. Lag time can also be a concern when using radiant floor heating, because when the system is initially turned on it can take a while for the heat to pump through the room, transfer through the material, and radiate upward throughout the space.

Benefits

Radiant floor systems can be significantly more sustainable than standard space and water heating systems; the combination of radiant technology and natural gas energy can also lower operating costs. The heating can be directed to specific zones or rooms using thermostat controls, also increasing efficiency. It is typically more efficient than baseboard heating and usually more efficient than forced-air systems because it eliminates duct losses. The comfort level of the spaces where radiant heating is used increases drastically when compared to most other systems. The heat is spread more evenly around the room, and cold spots or cold blasts of air from registers are no longer a concern; there is also no need to worry about cold floors! There are a variety of floor types that can easily be used with radiant floor heating.

These systems have no blower fans, so they are on the quiet side of heating systems. Dual purpose units that provide space as well as water heating can offer equipment cost savings. A radiant floor system also reduces allergies because it does not distribute the allergens that are distributed with forced-air systems. Hydronic systems used less electricity, and can use a wide variety of energy sources to heat the liquid, such as standard gas or oil-fired boilers, wood-fired boilers, solar water heaters, or any combination. Another benefit of using a radiant floor heating system is the relative humidity of the room easily increases; due to the method of heat transfer, the air in the room can be cooler, therefore increasing the relative humidity.