Radiant floor heating involves providing heat through the existing floor surface rather than using air ducts or baseboard heaters. The initial cost of underfloor heating is generally higher than other systems, as hot water piping or electrical wiring must be installed beneath the floor. However, this is offset by greater comfort and energy efficiency.
According to the US Department of Energy, space heating is the highest energy expense in American homes and accounts for, on average, about 45% of energy bills. Therefore, any improvements in heating performance and efficiency can generate an attractive return on investment.
Classification of underfloor heating systems
Most radiant floor heating systems are hydronic, which rely on hot water piping; or electrical, which use wiring or conductive mats under the floor. There are also air-heated installations, but they have very low efficiency, without offering significant advantages. Underfloor heating systems can also be classified based on their construction:
- In wet installations, hydronic piping or electrical wiring is embedded directly into a concrete floor or any other solid mass that can retain and emit large amounts of heat. It is important to emphasize that “wet installation” is not a literal term: the hot water remains inside the hydronic piping, releasing only its heat.
- In dry installations, on the other hand, piping and cables are installed in a void between floor layers or below the floor, but are not embedded.
Deciding which heat source and system construction to use is a matter of cost and benefit. The following are general guidelines for selecting system characteristics:
| Heating medium | Benefits | Disadvantages |
| Hydronic |
-Multiple heat sources available |
-Higher initial cost |
| Electric |
-Ease of installation |
-Higher initial cost |
Table 01-Hydronic VS Electric Radiant Heating
| System Construction | Benefits | Disadvantages |
| “Wet” or embedded |
-Better heat transfer and efficiency |
-Higher initial cost |
| “Dry” or not incorporated |
-Ease of installation |
-Air gaps around wiring or piping limit heat transfer and reduce efficiency |
Table 02- Construction of the “Wet” VS “Dry” System
For example, a dry construction radiant electric heating system will generally be the cheapest but least efficient option. On the other hand, a built-in hydronic system will likely have the highest initial cost but also the lowest operating cost.
Energy sources for radiant floor heating
The available heat sources depend on the type of heating system. Hydronic radiant heating is the most versatile option because any energy source capable of heating water is viable; the system can run on electricity, natural gas, oil, propane, biomass or solar radiation. Electric radiant heating systems are much more limited, as their design only allows for resistance-based heating.
Hydronic radiant floor heating
As previously stated, the main advantages of this configuration are versatility and energy efficiency. Homeowners with hydronic radiant heating can choose from a wide variety of energy sources:
- Boilers: They can be powered by natural gas, propane, oil or biomass, allowing owners to choose the cheapest option in their location. Electric resistance boilers can also be used, but their high operating cost negates the efficiency benefit of radiant heating.
- Heat Pumps: They are an economical alternative to electric resistance boilers. Although they also run on electricity, which is expensive in New York, but can equal the output of an equivalent resistance heater with just a fraction of the energy input. In many cases, heat pumps can compete with gas boilers due to their superior efficiency.
- Solar Collectors: Water heated by a solar collector can be used directly in a hydronic radiant heating system. If the available solar radiation is not sufficient to fully satisfy the heating load, the system can be supplemented with a boiler or heat pump. Solar collectors can achieve excellent results when hydronic piping is embedded in a concrete slab, as it essentially allows the sun's energy to be thermally stored for nighttime heating.
An engineering consultant or design firm can help you determine the best option for your home depending on your needs and site conditions. For example, solar collectors are not viable if your roof has shading issues, and gas boilers can be very expensive to install if your property does not have a chimney or service entrance of sufficient capacity.
Another advantage of hydronic heating systems is that a central heating unit can be used for both water and space heating, consolidating two building systems and reducing their total cost.
Electric underfloor heating
This system configuration is characterized by simple and inexpensive installation, but also by a very high operating cost. No central boiler or heating unit is required: electrical current is carried by the wiring and heat is generated locally. This type of system can be cost-effective when electricity rates are low and heating is only used for a few months a year, but this is not the case in New York.
Some electric radiant heating systems use conductive mats instead of wiring. The basic operating principle is the same, but the heat distribution is improved.
Comfort and Health Advantages of Radiant Floor Heating
Radiant floor heating systems offer comfort and health benefits that apply regardless of the energy source and system construction.
Improved comfort
Radiant heating systems work without fans and ducts, creating an even distribution of heat throughout interior spaces. Heat is radiated from the floor and then distributed by natural air convection. This eliminates some common problems in forced air systems that cause discomfort:
- Uneven heat distribution
- Noisy ducts
- Air currents
Health and air quality benefits
Another advantage of underfloor heating systems is that they cannot distribute allergens, volatile organic compounds (VOCs), or airborne germs because there is no forced air circulation. Furthermore, the ventilation system becomes independent of heating and can be designed specifically for indoor air quality.
Disadvantages of underfloor heating
As with all engineering decisions, radiant floor heating is not without limitations: it is generally higher priced and responds more slowly than other types of heating systems.
The cost of underfloor heating can be very high in existing buildings, as it is necessary to incorporate a new system into the existing floor. Installation becomes even more expensive if an embedded system is used, as it is necessary to pour a new concrete slab. Radiant floor heating is much more affordable in new construction, where floor installation costs are already part of the project's baseline and you only need to add one extra element.
Another disadvantage of radiant floor heating systems is that they take longer to heat an indoor space compared to forced air systems. However, this can easily be compensated for with automation: the smart thermostat can be set to pre-heat rooms when lower hourly electricity rates are being applied, saving energy in the process!
General recommendations for underfloor heating systems
The choice of construction materials is very important when it comes to underfloor heating. The Department of Energy recommends using ceramic tiles instead of wood, as ceramic can retain and emit heat more effectively. On the other hand, wood is essentially a form of insulation and reduces the efficiency of the system. Another disadvantage of wood floors is that they can crack in response to temperature changes.
Another recommendation, which applies not only to radiant floor heating but also to any HVAC upgrade, is to improve the building envelope before sizing new equipment. In this way, heating and cooling loads are reduced and new equipment can be sized smaller, increasing the potential for energy savings.
