Article No: 49

2006-05-01 09:57:45
Walking on Warm Floors
By: Carole McMichael

Beth Sifford of Sifford Creative Services and her husband wanted a home that would use the look of concrete to help create a peaceful and balanced atmosphere, which was the perfect setting for their art-oriented lifestyle.

Photo courtesy of Dan Frisch Photography

Dennis Spencer of Spencer Architects in Springfield, Mo., achieved these effects within the house by designing a long, freestanding natural-finished concrete gallery that is like a spine connecting the interior rooms. Outside, the Siffords have an " infinity pool" that has a waterfall at one corner, dropping 18 feet into another pool.

This single-story, slab-on-grade home design also adds to the balanced atmosphere by providing 2,800 square feet of concrete floors warmed by radiant floor heat. For that, Spencer turned to Robert Rohr, a designer, contractor and installer of radiant systems. He is also the owner of MaxRohr Radiant Heat, located in Rogersville, Mo.

"The radiant floor system is probably going to be the heating system for the entire house," Rohr said. "Concrete is one of the best applications for radiant heat because it makes the floor your heating system. All you have to do is put the tubing in there and circulate some warm water and you get a heating system by default. There is, however, a separate system for air conditioning that will come out of vents in the ceiling; and there is the potential for an air handling system through a furnace."

Radiant floor systems are most commonly heated electrically or hydronically. "I chose the hydronic system," Rohr said, "because I think it is better, based on the cost of the energy to run it. There is a place for electric systems in small areas and retrofitting, but when we talk whole-house applications, it is cheaper to use natural gas or LP to heat water in a boiler.

"Of course, wood fired boilers and geothermal systems also can heat the water that you circulate through tubes in the concrete. Even solar panels could be used. In fact, they create the ideal temperature needed for radiant floor heating. You can use radiant heat with other surfaces, such as wood flooring, but concrete works better because the thermal mass spreads heat out evenly."

Whole House Design

"When designing a radiant floor system for a whole house," Rohr continued, "I try to do more zoning, make it more user-friendly. For example, I can do various rooms separately, making this system more responsive to the owners' living patterns. The Sifford house has six zones with individual thermostat control. Each bedroom and the master bath has its own control.

"Even in the summer time, the bath can have radiant heat in the floors, the shower and tub walls. If your thermostat is set at 72 or 74 degrees, all the surfaces in your home are going to get to that temperature. But with radiant heat, we try to bring surface temperature up to your skin temperature, which is more like 82 to 85 degrees. When you step onto a radiant heated floor, it doesn't feel cold or warm, but neutral or right. When you get out of a hot shower, the floor feels cold even if it is 72 degrees.

"I put radiant heat in my concrete countertops in my own bathroom. We set towels on and underneath it, so they are nice and warm. Actually, it warms up the room and anything it touches. Radiant heat can be put in the ceiling as well."

Rohr noted that the cost of putting radiant floor heating in a stick-built homes as opposed to a concrete-built home is hard to compare because cost is all driven by house construction itself. The building dictates how much heat is needed. The tighter the construction, the less heat is needed. A concrete home made with insulated concrete forms is tighter than a stick-built one.

"Normally tubing is set 12 to 15 inches apart," Rohr said. "If you put it too far apart, you get 'striping,' which creates cooler areas between the tubes. Tighter spacing gives you consistent heating."

Step by Step

First, Rohr prepares a heat-loss calculation report. Using a software program, he enters the square footage, number and placement of windows and the type of insulation to determine the amount of heat needed. He then enters a design temperature-- usually zero degrees outdoors and 70 degrees indoors. In the North, he might use -10 or -20 degrees outdoors; in the South, it might go up to 10 degrees outdoors. The final result is a heat-loss calculation that indicates what size equipment he needs, the tube spacing and temperatures.

Next, Rohr submits a bid to the client. This bid presents the good, better and best options for heat sources and controls. For example, at the "best level," there is high-tech equipment for zoning and high-tech boilers that run 95 percent efficient. There is no denying that radiant floor heating systems are an upscale item, but according to Rohr, once people are aware of how comfortable the system makes a house, they would gladly give up other upscale options for radiant floors.

Finally, Rohr makes sure he and the builder, architect and contractors are on the same page, coordinating the installation and the pouring of the concrete. Rohr believes in doing good documentation: using videos, digital photos, measurements and little maps, so that if down the road, the owner wants to change the use of the home or move some walls, there is a record of where the tubing is.

Actual Installation

"First I lay down insulation," Rohr said, "usually a Styrofoam board from Dow or Owens Corning. Sometimes, if there are any moisture issues, I lay down a six mil vapor barrier underneath it. Next, I put down wire mesh to anchor the tubing at the proper spacing, so it doesn't float when the concrete is poured. The insulation is important because it can keep some of your heat from going into the earth and quicken the response time."

To make sure that there are no problems with the installation, Rohr uses air pressure that will stay on during the entire construction of the home. Tubing problems can be fixed with repair kits that are on site and the splices would be marked on his layout drawings. So far, he has never had a problem.

"It's not a big deal as long as you are told when someone has drilled through a tube," Rohr said. "You'd hate to have to go back two months later and see water bubbling up through the slab. The day before we pour, I'll put the air pressure on. Then, we have city inspectors come to check the pressure. If they are more savvy with radiant systems, they also will check the tubing spacing.

"The tubing connects to manifolds in areas where it comes up out of the slab to create different zone configurations. Depending on the layout of the house, all the loops can go back to the boiler. The manifolds are often housed in closet areas. A separate line then goes back over to boilers. In the Sifford house, which follows a long narrow layout, we have two different manifolds in bedroom closets. Sometimes, it will be poured in the slab, and sometimes it will go up through the framing through the studs and overhead, depending on the path of least resistance.

"Typically, the slab is 4 inches. Now the beauty of the concrete slab comes out. You can start staining it and/or stamping it with designs. The Sifford house uses a saw-cut design in the shape of a huge grid, so it looks like tiles. The same could be done with countertops. Some of the jobs I've seen look like they are acid etched or made of leather."

Keeping It Working

"Very little maintenance is required for hydronic systems," Rohr said. "You want to be careful about the quality of water you use; put in some corrosion inhibitors to protect your boiler and different components. There is no duct work to be cleaned out or filters to be changed. It is a good idea to have a yearly inspection of the boiler, as you would service anything mechanical. Savvy contractors are selling systems with maintenance contracts. I like to do that as a free service because I want to hear how my customers like the system and if there are any adjustments to the zoning, which is done through the electric thermostats. That is the beauty of radiant heat, it is infinitely adjustable. You could have each room set at a different temperature if you wanted. There are all kinds of controls, including weather-responsive controls that automatically change the temperature setting as the outdoor temperature changes."

Rohr noted that the efficiency of adjustments depended on how rooms were going to be used. If the kids are in college and only there on holidays or you have a guest or hobby room that is used only occasionally, you can set the temperature down to 60 degrees. It isn't efficient to set it back every night and ramp it up every morning because radiant heat systems don't respond as quickly as forced air systems. However, unlike forced air heating, radiant systems don't lose their heat level with the opening and closing of doors in cold weather because the slab is still warm. It is better to leave the setting at the temperature that works most of the time.

The use of rugs or carpets is something you have to be concerned about when planning on radiant floor heating. "Using carpeting is like putting insulation over the heating system," Rohr said. "Clients have to be careful with the choice of carpet and padding. There are some pad products, which are thinner and denser, that are made especially for use with radiant heat. A thick carpet is obviously a bad match with a radiant heat systems, but throw rugs are not a problem. Use of floor covering is something the installer needs to be aware of so he can design the system around it. If there is going to be carpet in a room, we would set the tubing eight inches on center, rather than 12 or 15 inches, to get more heat output."

The Right Choice

When a client chooses a contractor, they should check with the Radiant Panel Association (RPA) through its Web site: RPA has a certification for designers and installers, and information on products specific to the radiant heat industry. They also have testing and rating information. Anyone associated with that group has access to good training and the latest equipment and product development.

There is also another site at This provides a directory for contractors for the various kinds of heating systems. Naturally, clients should find someone who has experience with radiant heat installation.

Word of mouth and connections with major manufacturers have been Rohr's most effective marketing, but he pointed out that the best sales pitch is to get people to walk on a heated floor.