Radiant heating systems provide heat through the floor, walls, or ceiling of a building. As their name suggests, these systems are primarily based on radiant heat transfer – direct delivery of heat from a hot surface to occupants and objects through radiation.
Underfloor heating systems are characterized by their silent operation and energy efficiency. Because the heat source is located below, the temperature rise is uniform as the warm air rises and displaces the cooler air. This also allows heating to occur without a forced air system: the installation does not disturb dust and allergens, while improving occupant comfort by eliminating drafts. Radiant floor heating also offers a lower operating cost than furnace-based heating systems—you can expect savings of 25% to 50%, according to the U.S. Department of Energy. Space heating is the largest energy expenditure in New York buildings, so projects that improve efficiency tend to have an excellent return on investment.
Underfloor heating is a great option for homes with children and schools. Conventional air duct systems deliver heat from above, and the lower part of the room is not always heated effectively because the hot air tends to rise. Due to their shorter stature, children are more susceptible to uneven heating from forced air systems, and this can potentially lead to health problems. Radiant floor heating, on the other hand, provides heat from the bottom up and improves children's comfort.
Radiant heat systems are highly recommended in homes with large rooms and high ceilings. Conventional forced air systems are impractical in these cases, as they tend to only heat the upper part of the room, wasting energy.
Types of radiant floor heating systems
Radiant floor heating systems can be classified based on the medium used to provide heat: air-heated, electric, and hydronic.
1) Air-heated underfloor heating system: In this system configuration, hot air is blown through ducts beneath the floor, which causes a heating effect. The main limitation is that the air cannot retain much heat, so these systems are not suitable for residential buildings.
2) Electrical underfloor heating system: This configuration uses heating cables or conductive plastic mats embedded in the floor. The main limitation of electrical underfloor heating systems is their dependence on resistance heating, which can result in very high operating costs if the kilowatt-hour price is high.
Electric radiant floor heating works best for homeowners who have access to point-of-use electricity rates and floors with high thermal mass (e.g. concrete). The system can be set to operate when electricity prices are low, which is typically off-peak hours , storing as much heat as possible in the floor itself. The system is also set to shut down during peak demand times with expensive electricity, and the floor can provide 8 to 10 hours of energy-free heating if its thermal mass is high enough. If the floor has a reduced thermal mass, the RFH electrical system must operate more frequently and operating costs can increase dramatically during peak demand times.
3) Hydronic (hot water) underfloor heating system: This is the most popular and economical among the three types of underfloor heating systems and is suitable for applications where occupants can use a thermostat to control heat production room by room. Hot water from a boiler is pumped through hydronic pipes that are evenly distributed under the floor, and distribution between the different pipes is controlled using a collector. Hydronic RFH systems have minimal maintenance requirements and can be installed between joists under existing floors, making them ideal for renovations.
Types of underfloor heating installation
Underfloor heating systems can be classified into wet and dry installations. Note that this classification is independent of the heat transfer medium: the words wet and dry do not refer to hydronic piping or electrical resistance.
1) Wet installation: This is the oldest type of underfloor heating installation. Electrical cables, mats, or hydronic tubes are embedded in a thick concrete slab or thin concrete subfloor, which means this type of installation is more expensive than dry. The RFH system takes longer to heat the floor and room air, but the large thermal mass of concrete preserves the heating effect for several hours after the system is turned off.
2) Dry Installation: A dry installation is easier to set up, cheaper, and generally the most convenient type. Heating cables, mats or pipes are installed in an air pocket under the floor, not embedded in the concrete, resulting in faster heating than a wet installation. However, this system configuration needs to operate at high temperature since it is not embedded in the flooring material.
How Floor Materials Influence Performance
The performance of underfloor heating is strongly influenced by the floor material: thermally conductive materials improve performance, while insulating materials are detrimental. However, this doesn't mean you should avoid insulation – just make sure it's not installed in a location where it could block heat transfer between the underfloor heating system and interior spaces.
Due to its high thermal conductivity and storage capacity, ceramic tile is considered the most effective covering material for radiant floor heating. Other materials, such as vinyl and linoleum, provide excessive insulation, thereby reducing the system's efficiency. Wood floors conduct heat very well, but laminate wood floors are preferable to solid wood, which can dry out and contract easily.
Read more about thermal mass flow meter and its working principle
How do radiant panels work?
Unlike underfloor heating systems, these panels are generally installed on walls and ceilings, using electricity or hot water to heat aluminum sheets. Electrically heated systems offer the convenience of avoiding water leak issues, but they also have a much higher operating cost due to their dependence on electricity. Radiant panel systems can have a surface construction or can be embedded in the wall, but keep in mind that future changes are unfeasible in the second case.
What are the main components of underfloor heating systems?
1) PEX piping/heating cables/heating mats: This part of the system is responsible for providing heat. PEX piping distributes hot water from a boiler, while the other two options produce heat directly through electrical resistance.
2) Collector: Distributes hot water between several hydronic piping circuits.
3) Actuator Valves and Fittings: Valves allow control of water flow, while fittings provide connection between piping and other system components.
4) Control package: Operates the system based on user settings.
5) Heating control (thermostat): Allows the user to set the required temperature.
Benefits of Radiant Floor Heating
1) RFH is suitable for new construction with large spaces and high ceilings, improving both performance and comfort.
2) Easily adjustable comfort levels and heating controls.
3) Energy savings and reduced bills.
4) More headroom is available by eliminating forced air systems and their associated ductwork.
5) Air moves by natural convection, minimizing the spread of dust and allergens.
6) Quiet operation
7) Universal control
