Founder | BPI® Energy Auditor Certified Professional
Radiant floor heating is an effective and energy-efficient way to warm a specific area, whether a house, a room, or any other zone.
Radiant floor heating is an ideal option for new homes. However, the advent of viable retrofitting installation has made a radiant floor heating system a practical and beneficial alternative for those remodeling their homes.
Radiant floor heating doesn’t work the same as furnaces, heat pumps, or electric space heaters.
So how does radiant floor heating work? Read on to learn more.
How Does Radiant Floor Heating Work?
Radiant floor heating works through an underfloor installation of a hydronic or electric system that heats the floor within a room, zone, or home. The type of radiant floor heating system and installation determines the tech behind it.
The Tech Behind Radiant Floor Heating
The tech behind how radiant floor heating works follows the fundamental principles of heat transfer and thermodynamics:
- There’s a network of heated conduits underfloor (usually located in the floor screed or subfloor).
- When these conduits are hot, they radiate and conduct heat through the subfloor, underlayment, and floor.
- As a result, the floor warms up and transfers heat to a specific area.
Note that this heat transfer also happens through convection. In other words, radiant floor heating systems don’t only make use of infrared radiation.
That said, all radiant floor heating systems rely on the same laws of thermodynamics and mediums of heat transfer.
Does It Use a Furnace?
Radiant floor heating does not use a furnace because the most popular systems are either hydronic or electric. Air-heated radiant floors are neither widespread nor viable. Therefore, a furnace has no utility or purpose in electric or hydronic radiant floor heating.
Air-heated radiant floors exist, but they aren’t energy-efficient. Also, using forced-air systems defeats the purpose and benefits of radiant floor heating.
The type of radiant floor heating system determines the heat source.
The most common radiant floor heating systems are:
- Hydronic (using boilers or water heaters)
- Electric (using electricity or solar power)
Hydronic Radiant Floor Heating
The most popular radiant floor heating system is hydronic. A hydronic system is perfect for an entire house, especially considering the operating cost of radiant floor heating.
Also, there are different types of hydronic radiant floor heating systems.
All hydronic radiant floor systems use water as the conduit or medium to transfer heat. But the specific type or system determines the installation and how the tech works.
Broadly, you can classify hydronic radiant floor heating into two types:
- Wet installation
- Dry installation
The wet installation method has two variants, whereas the dry system has more options. Regardless of these differences, the tech behind hydronic radiant floor heating is the same:
- A network of tubes (usually PEX A) is installed underfloor. Again, this is generally in the floor screed or on top of the subfloor. These tubes circulate hot water to heat the subfloor, underlayment, and floor in a specific area.
- The underfloor tubes are connected to a manifold, hooked to a boiler or water heater in your home.
- Pumps and actuators circulate the hot water from the boiler or heater throughout these pipes under the floors.
- Using an appropriately sized boiler or water heater, you can install a hydronic radiant heating system for an entire property.
If you’re familiar with radiators, you may wonder how radiant floor heating differs. Most radiators use either hot water or steam. Radiant floor heating uses hot water. But the difference lies in the way the two systems heat a room.
Radiators are installed above the floor and heat the air around the fins. This warm air heats the room through convection. However, since air isn’t the most effective heat transfer medium, conventional radiators aren’t as efficient or effective as radiant floor heating.
Radiant floor heating warms the subfloor first and then the objects in contact with it, like your feet and furniture. The underfloor system doesn’t warm the air in a room until there’s a substantial heat difference between the radiating source and ambient indoor temperature.
Even when radiant floor heating warms the indoor air, it starts at the bottom and not at a height, which radiators do. Therefore, warm air rises from the floor, effectively heating the space around you. This convection heat transfer enhances the efficiency of such systems.
All hydronic radiant floor systems have the same effects and benefits. The main difference lies in the installation.
Wet Installation of Hydronic Radiant Flooring
Arguably, the most sustainable hydronic radiant floor heating system is a wet installation. This method uses poured concrete in the floor screed or atop the subfloor to house the PEX A pipes or tubes. But this method isn’t always feasible for some floors or if you’re remodeling.
Here’s how a wet installation of hydronic radiant floor heating works:
- The PEX A pipes are laid out with guide rails as a part of the floor screed.
- Poured concrete forms a slab under, around, and above the tubes or pipes. This concrete slab becomes the subfloor for any floor or an entire property.
- A concrete sheet is used if there’s a subfloor that won’t support a slab. The concrete sheet envelopes the pipes and becomes the thermal mass.
Subsequently, you can choose compatible flooring material for the floor.
Here’s a short YouTube video about how wet installations of hydronic radiant floors work:
All wet installations connect to a manifold and water heating appliance. You can use a boiler to supply the hot water, whether it runs on gas or oil. You can also use a wood-fired boiler if that’s more practical. A water heater can work well if the radiant floor heating zone isn’t too large.
Small setups can use solar water heaters. But larger installations require condensing boilers. These considerations factor into the different types of dry installations of hydronic radiant floor systems.
Dry Installation of Hydronic Radiant Flooring
There are different types of dry installation of hydronic radiant floor heating systems.
They include:
- Under the subfloor, such as between joists
- Over the subfloor, i.e., boards, tracks, etc.
Dry installations also use tubes or pipes like PEX A but don’t involve concrete slabs or sheets. Instead, the lines are installed under or above the subfloor. This approach facilitates remodeling or retrofitting, whereas wet installations are more conducive to new construction.
If you choose a dry installation under the subfloor, the radiant floor system or its pipes should have reflective insulation, so the heat is directed upwards. Otherwise, the hot water in the pipes will warm the space below.
This brief YouTube video shows the kind of insulation you need for a dry installation of a radiant floor heating system under the subfloor:
Likewise, if you go for a dry installation above the subfloor, you must use boards or tracks with underlying insulation. Otherwise, you must have reflective insulation, vapor barrier, and anything else that the manufacturer or installer may recommend.
Furthermore, radiant heating isn’t necessarily compatible with all types of flooring, whether wet or dry. For example, while hardwood and tiled floors are usually not a concern, carpets with thick padding may not work because they prevent efficient heat transfer from the subfloor.
Electric Radiant Floor Heating
Electric radiant floors use wires, mats, or meshes instead of hot water pipes on the subfloor. Resistance heating wires, such as nichrome, generate heat when current runs through them. This heat is transferred to the floor and onto a room or zone.
All electric radiant floor systems use resistance wires like nichrome, an alloy of nickel and chromium. Nichrome is used in traditional electrical appliances like toasters. But companies manufacture different kinds of resistance wires, such as Kanthal A-1.
The mats or meshes are polymer mats that don’t have electrical conductivity. The most popular insulating material for such mats or meshes is a fluoropolymer.
These differences aside, electric radiant flooring is easier to install, as there’s no need to redo the subfloor.
Homeowners can place the mats or meshes on a subfloor, and you can install tiles with thinset mortar. The tiles or their adhesives won’t affect an electric radiant floor heating system.
The only concern with electric radiant floors is financial feasibility due to electricity costs, especially at peak rates. Boilers running on gas or oil are more affordable to run. Therefore, electric radiant floor heating is most appropriate for small spaces (i.e., kitchens, bathrooms, etc).
Air-Heated Radiant Floors
Air-heated radiant floors aren’t as viable or worthwhile as hydronic or electric systems. An air-heated radiant floor has the same drawbacks as ducted heating systems. You’ll bear the cost of heating the air that will inevitably lose the heat in transit instead of warming you or the rooms.
Final Thoughts
Radiant floor heating needs little maintenance over time. Hydronic setups are superior to electric systems, but both offer some flexibility.
For instance, hydronic systems may use a boiler or water heater with power sources such as gas, oil, heat pump, and solar.
Likewise, electric radiant heating may use grid power or solar energy. But if you plan to use off-peak rates, electric setups have no advantage because there’s no thermal mass to store the heat energy.
In contrast, concrete slabs or sheets in hydronic systems can stay hot for hours.