Engineers confidently are specifying radiant floor heating systems to resolve difficult heating challenges.

Radiant floor heating is getting a lot of attention these days, and growth of this market is profound. But those who specify systems for commercial and industrial buildings seem slow to recommend anything remotely new. Maybe they fear customers won't accept it or that it will cost more. Or maybe they just don't know of the benefits that radiant heating offers. Engineers who have specified the technology have been very successful. Radiant floor heating purists consider every concrete pour without radiant floor heating as another lost opportunity.

A number of commercial and industrial heating engineers are confidently specifying radiant floor heating systems to resolve their most difficult heating challenges. Difficult areas to heat often contain high ceilings, weather-exposed floors, floors with high back losses and large amounts of air infiltration. These conditions are commonly associated with atriums, buildings with parking garages and buildings with large entranceways. Floor heating systems can also help to dry floors that need frequent mopping, thus minimizing "slip and fall" cases. Floor heating systems are also virtually maintenance-free.

Candidates for radiant floor heating include:

  • Office buildings

  • Convenience stores

  • Schools

  • Hospitals

  • Restaurants

  • Hotels

  • Manufacturing plants

  • Malls

  • Retirement homes

  • Nursing homes

  • Bus garages

  • Fire stations

Then and now

Although radiant floor heating is not a new technology, North American engineers rarely specify radiant floor heating as their primary heating system. Like hot-water radiator heating systems, radiant floor heating was widely used to heat many projects during the late '40s and '50s. Engineers stopped working with radiant floor heating during the late '60s and '70s because of several reasons:

1) Leaks started showing up from the corrosion of the steel or copper piping systems.

2) The thermal mass properties of the slab made the systems difficult to control.

3) There were higher installation costs associated with steel or copper piping systems.

4) Electrical companies instigated promotional programs to introduce the heat pump.

Beginning in the late 1980s, radiant floor heating made a comeback in the residential market because of some key industry changes:

1) Introduction of plastic pipe made from cross-linked polyethylene (PEX)

2) Introduction of electronic controls, boilers and circulators designed for radiant floor heating

3) Installation components, manifolds and flexible plastic pipe were designed to be installed as a system, thus reducing installation time, cost and skills required of the installer.

4) Building owners discovered that they missed the comfort associated with hot-water heating systems, both hydronic radiation and hydro-coils.

The challenge now for the radiant floor heating industry is to reintroduce these heating concepts with the new technology to a skeptical clientele in the commercial/industrial realm.

PEX pipe

While the United States had its sights on the moon during the late '60s and early '70s, Europe was busy developing PEX. Both the peroxide (PEXa) and electron (PEXc) methods had a strong performance rating and have continued to satisfy European specifying engineers for more than 25 years.

With the removal of Polybutylene (PB) resins from the U.S. market for pipe production in 1996, another type of PEX was introduced to the U.S. market manufactured by the silane (PEXb) method. The silane compounds used to make PEX worked in the same extrusion machinery used to make PB. Companies that were making PB were getting into the PEX business within months after their PB resin shipments stopped. (Modern Plastics, May 1996, "Extruders eye options after Shell halts PB pipe-resin sales in U.S.")

This changed the market for PEX considerably because PEX did not have a competitor in PB competing for the plastic pipe market share. With the former PB extruders making PEXb, marketing efforts for the use of PEX greatly increased. PEXa and PEXc have been in wide use in the U.S. market for the past 10 years. And PEXb is now going into its second year. Engineers who want to learn more about PEX can contact the High Temperature Division of the Plastics Pipe Institute (PPI) at 202-974-5318 or visit

Modern controls, circulators and boiler systems

As with the entire HVAC industry, the growth of radiant floor heating has greatly benefited from the advent of electric control systems. The ability to measure the outside air temperature, sun loads and occupancy levels and then to adjust the output of the system accordingly provides the control necessary in preventing thermal lag associated with floor heating systems of the past. Pump companies and boiler manufacturers are now designing circulators with radiant floor heating systems as part of their pump design criteria. Radiant floor heating is attributed to increasing both residential pump and boiler sales over the past five years, bringing renewed sales for the new-home market.

Radiant floor heating system suppliers

As the U.S. market for radiant floor heating has grown by 25 percent every year for the past 10 years, the number of companies that specialize in selling these systems has also increased. Radiant floor heating companies vary in their capabilities and products, and a recent trend finds some offering complete systems, technical training, software, technical literature and a technical support department. But some companies selling radiant floor heating still lack the technical expertise to assist with projects in the commercial/industrial market. Besides technical expertise, the radiant floor heating companies that are supporting these types of projects typically need to offer larger sizes of PEX, qualified fittings and other specific components.

A knowledgeable technical staff within the radiant floor heating company is critical when assisting the specifying engineer. Some system suppliers offer CAD assistance, which allows for the use of CAD software and e-mail, enabling companies to easily work together from a distance. Floor heating companies can serve the engineering office by adding drawings and specification details directly to the engineer's drawings, freeing up valuable time of the drafting staff at the engineering firm. And the manufacturer's engineering staff at the floor heating company can assist the engineer with design. These methods are no different than what an engineer would expect with the specification of any other equipment, and the amount of engineering work required to design a radiant floor heating system is basically the same as what is required to design a heat exchanger or a cooling tower.

Contact the Radiant Panel Association (RPA) at 800-660-7187 or visit for a listing of companies that offer such services.

Cost considerations

Initial cost decisions often outweigh long-term benefits of lower operating cost and optimized comfort in the minds of the builders. Heating and cooling should be viewed as part of the life support system for the building. Imagine if the structure or the skeleton of the building was neglected to save cost. Engineers that investigate, learn and embrace new heating and cooling technologies and learn how to design them interdependently hold the keys to the future. Presently most commercial/industrial structures incorporate a concrete slab (thermal mass for floor heating), with probably less than 1 percent of these slabs containing a radiant floor heating system.

Understanding the benefits of each type of heating and cooling technology has led designers to specify complete systems that save money and provide the ultimate in comfort for their clients. These types of system designs are known as hybrid systems. A hybrid system is an interdependent design of various heating and cooling technologies. Typical hybrid systems being designed and installed today will include radiant heating, air heating and cooling, and modern computerized control systems. As engineers become more familiar with the integration of these technologies, the future will include radiant cooling, desiccant air conditioning and the mean radiant temperature measuring devices as standard components. These new technologies will help correct many of the indoor air quality (IAQ) problems that are now discovered in pre-existing heating and cooling systems.

Dispelling myths of radiant floor heating

Myth 1: The cost of ductwork has to be included for the cooling system, and therefore heating should be provided through the same ducts.

Following the concept that cool air falls and hot air rises, air ducts for cooling work best when they are placed nearer the ceiling than the floor. Buildings with high ceilings are definite candidates for a floor heating system. But many buildings are designed with air convection cooling and heating ducts placed in the ceiling.

With air convection systems, air heating will heat the ceiling of the building to temperatures that are 20° F to 30° F higher than what is required for human comfort. Hot air cools and falls to where the heat is required, cooling to 68° F. Simply introducing heating through the duct works because they are already there seems to be a "cheapening" of the building. The greatest "cost" is really in the loss of comfort.

Myth 2: The cost of adding PEX to concrete floor is prohibitive.

Most commercial and industrial building projects use concrete as part of the flooring system, unlike residential buildings where a majority of the floors are made from plywood. Because concrete is already being used, why not install PEX and make the floor a giant radiator? The cost per foot of pipe is generally minimal when compared to the cost of other building components.

Myth 3: Installation of the radiant floor heating systems will disrupt the construction sequence and cause unnecessary problems on the job site.

Mechanical contractors who have installed a radiant floor heating system in a commercial/industrial building have found that with proper training and coordination with the general contractor and other trades, the installation goes smoothly and does not interfere with the planned construction schedule. PEX pipe is durable and tough enough for normal job site conditions.

For most projects there is little if any impact on the concrete floor installation or any other construction event associated with the floor heating system if normal planning practices occur. Design/build engineering firms have found that radiant floor heating expertise is a great way to grow their business, creating a niche that attracts customers and separating them from their competitors.

Myth 4: Engineers, contractors and control companies are not experienced with the design, integration and installation of radiant floor heating systems with other HVAC systems.

Integrating a floor heating system with other heating and cooling systems is not difficult for the experienced engineer. A floor heating system is basically the same as other heating or cooling equipment for the project. Manufacturers who offer design assistance can provide heat output for the floor system being designed and aid with the requirements of both the heating plant and the distribution piping. Control companies can either integrate controls they are familiar with or use any of the new controls that are available.

Interdependent, hybrid designs are the future of heating HVAC technology. Engineers who learn how to bring different heating and cooling technologies together to meet the parameters of a design will be the ones who can protect or gain their share of the HVAC market. For building owners, the choice of an experienced engineer is as critical as the choice of experienced contractors,

Myth 5: Placing equipment anchors in the floor will ruin the floor heating system.

Avoiding equipment anchors when installing floor-heating pipe is no different than what the installing contractor must avoid for electrical conduit or drainage pipe systems. Proper planning is always the key. Installing landings for stairwells or any other structural component should be planned in advance, and pipe can be laid away from these anchor target areas. Architectural drawings that specify anchor bolt locations greatly aid the engineer with the layout parameters of the floor heating pipe, The same is true for expansion joints, saw cuts and reinforcement bar depths for the structural slab or floor.

Myth 6: Floor heating will not provide enough heat for the structure.

Performing and determining a heat loss based on the total air volume for the space could lead to a heating requirement that is far greater than what is required to size a floor heating system. Take the total volume for a 40-foot-high space-most likely, normal heat loss engineering calculations will lead to a heating requirement of approximately 45 Btuh per square foot. If the engineer specifies a floor heating system to provide the amount of heat needed to heat the space, 25 Btuh per square foot may be all that is required for the comfort of the building's occupants.

Measuring a room's air temperature is not completely representative of how warm the occupant feels in the room. Mean radiant temperature-or the effect of heating being transmitted by the surrounding objects and building components of the room-has a big impact on the warmth a person feels. Because warmth goes to cold, and humans are emitters of heat, if we are losing a higher percentage of heat than we are receiving, we feel cooler. Warm air does not heat objects as efficiently as irradiated heat from a floor heating system. Floor heating is a constant source of energy that keeps walls, furniture and other parts of a building at a constant warm temperature.

Most of us have been to a football or baseball game on a cold day with the sun hiding behind a cloud. When the sun came from behind the cloud, we felt much warmer. But the conditions around us-wind and surroundings-did not change. If a radiant floor heating design is based on the allowable floor surface temperature for the floor heating system, then the floor capacity for the heating system is determined with a simple calculation-the floor surface temperature less the desired temperature for the room multiplied by a factor of two. This calculation will provide the total Btuh per square foot for the floor heating system.

Many technical papers have been written on the subject of radiant floor heating, sizing and output. Responsible manufacturers involved in radiant floor heating have incorporated this information into their technical manuals. The American Society of Heating and Refrigerating and Air-Conditioning Engineers (ASHRAE) provides an excellent source for technical information associated with radiant floor heating. And ASHRAE's 1992 HVAC Systems and Equipment Handbook, Chapter 6 "Panel Heating and Cooling," is a great starting place for understanding the finer points of radiant floor heating. ASHRAE can be reached at 800-527-4723 or visit

Opportunities for radiant floor heating projects in the commercial/industrial sector of the heating industry are all around us. Radiant floor heating is just another "piece" of equipment for commercial/industrial projects. The same benefits of comfort and energy savings that are growing the residential market exist for this market. The education of building owners by the engineering community will in turn benefit both the owner and the engineer. The owner will save on energy costs and will increase comfort levels. The engineer will benefit from a satisfied customer, which should lead to many new job referrals. The future is bright for those who invest time in learning and designing with all the available heating technologies, and who can put this interdependent design philosophy to work.