Radiant floor heating consists on delivering heat through the existing floor surface, as opposed to using air ducts or baseboard heaters. The upfront cost of radiant floor heating is generally higher than that of other systems, since it is necessary to install hot water piping or electrical wiring under the floor. However, but this is compensated by improved comfort and energy efficiency.
According to the US Department of Energy, space heating is the highest energy expense in American households, and represents around 45% of energy bills on average. Therefore, any improvements to heating performance and efficiency can yield an attractive return on investment.
Classification of Radiant Floor Heating Systems
Most radiant floor heating systems are either hydronic, which rely on hot water piping; or electric, which use wiring or conductive mats under the floor. Air-heated installations also exist, but they suffer from a very low efficiency without offering any significant advantages. Radiant floor heating systems can also be classified based on their construction:
- In wet installations, hydronic piping or electrical wiring is embedded directly in a concrete floor, or any other solid mass than can hold and emit large amounts of heat. It is important to note that “wet installation” is not a literal term: the hot water stays inside hydronic piping, releasing only its heat.
- In dry installations, on the other hand, piping and cables are installed in an empty space 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:
-Various heat sources available
-Higher upfront cost
-Ease of installation
-Higher upfront cost
Table 01-Hydronic VS Electric Radiant Heating
|"Wet" or embedded
-Improved heat transfer and efficiency
-Higher upfront cost
-Ease of installation
-Air gaps around wiring or piping limit heat transfer and reduce efficiency
Table 02-"Wet" VS "Dry" System Construction
For example, an electric radiant heating system of dry construction will generally be the cheapest but least efficient option. On the other hand, an embedded hydronic system is likely to have the highest upfront cost but also the lowest operating cost.
Energy Sources for Radiant Floor Heating
The heat sources available 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 with electricity, natural gas, oil, propane, biomass or solar radiation. Electric radiant heating systems are much more limited, since their design only allows 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: These can be fired by natural gas, propane, oil or biomass, allowing their owners to choose the cheapest option at 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 a cost-effective alternative to electric resistance boilers. Although they also run with electricity, which is expensive in New York, but can match 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 enough to meet the heating load completely, the system can be complemented with a boiler or heat pump. Solar collectors can achieve excellent results when hydronic piping is embedded in a concrete slab, since it essentially allows energy from the sun to be stored thermally 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 instance, solar collectors are not viable if your rooftop has shading issues, and gas boilers can be very expensive to install if your property lacks a chimney or service entrance of enough 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 Radiant Floor Heating
This system configuration is characterized by a simple and cheap installation, but also a very high operating cost. No central boiler or heating unit is required: electric current is carried by wiring, and heat is generated locally. This type of system can be cost-effective when electricity rates are low and heating is used for only a few months each year, but this is not the case for New York.
Some electric radiant heating systems use conductive mats instead of wiring. The basic operating principle is the same, but 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.
Radiant heating systems operate without blowers and ducts, creating a uniform heat distribution throughout indoor spaces. Heat is radiated from the floor, and then distributed by natural air convection. This eliminates some issues that are common in forced-air systems and cause discomfort:
- Uneven heat distribution
- Noisy ducts
Health and Air Quality Benefits
Another advantage of radiant floor heating systems is that they can’t distribute allergens, volatile organic compounds (VOCs) or airborne germs because there is no forced air circulation. In addition, the ventilation system becomes independent from heating and can be designed specifically for indoor air quality.
Disadvantages of Radiant Floor Heating
As in all engineering decisions, radiant floor heating is not free from limitations: it generally comes with a higher price tag, and responds more slowly than other types of heating systems.
The cost of radiant floor heating can be very high in existing buildings, since it is necessary to embed a new system within the existing floor. The installation is even more expensive if an embedded system will be used, since it is necessary to pour a new concrete slab. Radiant floor heating is much more affordable in new constructions, where floor installation costs are already part of the project baseline and it is only necessary to add one extra element.
Another disadvantage of radiant floor heating systems is that they take longer to heat an indoor space, compared with forced-air systems. However, this can be easily compensated with automation: smart thermostat can be configured to preheat rooms when the lowest hourly electricity rates are being applied, saving energy in the process!
General Recommendations for Radiant Floor Heating Systems
The choice of construction materials is very important when dealing with radiant floor heating. The Department of Energy recommends the use of ceramic tiles instead of wood, since ceramic can hold and emit heat more effectively. On the other hand, wood is essentially a form of insulation and it reduces system efficiency. Another disadvantage of wood floors is that they can crack in response to temperature changes.
Another recommendation, which applies not only for radiant floor heating but for any HVAC upgrade, is to improve the building envelope before sizing the new equipment. This way, heating and cooling loads are reduced and the new equipment can be sized smaller, increasing the energy-saving potential.