Hot Water Radiant Floor Heating Installation Options using PEX Tubing For concrete floors (slab on grade), the radiant PEX tubing is attached to the reinforcing mesh with cable ties before the slab is poured. This type of radiant floor has a large mass. With this type of radiant floor the space it is heating can only changed by the radiant floor about 1/2 a degree per hour. Typically the water temperature used in this type of radiant floor is between 90° and 115° Fahrenheit. It is imperative that the surface temperature of any Radiant floor stays below 85° or it becomes uncomfortable. Radiant Concrete Floors (Slab on Grade) Photo courtesy of REHAU Simpler in new construction but you can install this type of radiant floor as a retrofit, the radiant PEX pipe is installed over framed floors and covered with concrete or lightweight concrete. We like this type of radiant floor heating the best. Very easy to install and it provides a very even heat. Thin slab radiant floors have a much quicker response time. With this type of radiant floor the space it is heating can be changed by the radiant floor as fast as 2 a degree per hour. Thin slab radiant floors have many floor covering options. (tile, stained concrete, wood using sleepers, carpet, etc.). Typically the water temperature used in this type of radiant floor is between 90° and 125° Fahrenheit. A quick note: When installing this type of radiant floor you need to have a tension break between the concrete and the wood substrate to allow the concrete and the wood floor to expand and shrink at there own rates. We recommend using 6 mil. sheet plastic. Thin Slab over wood framing. Photo courtesy of REHAU In a typical remodeling project, the PEX radiant tubing is snapped into radiant heat transfer plates which radiate heat to the floor above. The radiant heat plates tend to make the floor above them have warm and warmer spots. Still very comfortable. The installation of PEX under floors has its draw backs. PEX when heated expands 1.1 inch per. 10 feet with a 100° temperature rise. Typically the temperature for this type of installation is between 120° and 145° Fahrenheit. If not properly installed this radiant floor can be quite noisy. Under floor installation using Radiant Heat Transfer Plates Photo courtesy of REHAU In a not so typical remodeling project, the PEX radiant tubing is hung in plastic hangers below the floor about 1 inch. This allows the PEX radiant tubing to slide a little and sag a little as it expands making for a quiet floor. The hot water running through the PEX radiant tubing heats the air which intern heats the floor above. A insulation with a reflective surface mounted facing up leaving a 3 to 4 inch air space to the bottom of the floor is required. The radiant heat from this floor system is very even. The air in this space must be stagnant, meaning all penetrations must be calked and the floor joists where they meet the band joist also. The installation of PEX radiant tubing under floor in this manner is NOT described in REHAU PEX installation manuals. There for it would NOT be Warranted. Typically the temperature for this type of installation is between 120 deg. and 165 deg. Fahrenheit. We know of two houses using this method. Both new construction. One in Vermont where tubing was hung 16 inches on center and the water temperature is run at 180 deg. straight out of the boiler. It has kept the house at 68 deg for fifteen years now, no hot spots, no noise. One in Oregon and one in Vermont with the PEX 8 inches on center and the water temperature is set at 140 deg. Both installed for 3 years and to this date no noise, no problems. PEX radiant tubing hung under floor using air space and reflective insulation. Photo courtesy of REHAU Radiant Heat Main Page