PEX Radiant Heat System FAQ's
1. Ways to install Radiant PEX with an existing floor
PEX Tubing Under Floor - Typically under hardwood or tile flooring
PEX In Floor - Typlically in poured cement
PEX Over Floor - Typlically using ThermalBoard, VersaTherm or Creatherm Radiant Heat Mass
2. Radiant Slab on Grade
For residential slabs we recommend 1/2 Inch PEX tubing to be 12 Inch on center. Along walls with lots of glass or high heat loss the PEX should be 6 Inch to 9 Inch on center on the outside walls for the first 2 feet, and 12 Inch on center everywhere else.
When figuring the over all length of tubing you will need you divide any 6 Inch spacing area by .5, divide any 9 Inch spacing area by .75 and any 12" spacing area by 1. This will give you the over all length of the PEX needed in the slab. You will need to add the length of tubing needed to get up to the pex manifold.
Typically pex manifolds are mounted 18 Inch to 24 Inch off the slab.
3. Installing PEX Tubing
Following good piping practices the maximum length of each 1/2 Inch PEX tubing runs should be no longer than 300 feet (300-foot maximum is code in many places). When the pipe loops exceed 300 feet you need to use larger circulators (pumps) to maintain this temperature drop. With larger circulators initial cost is higher and they usually require twice as much electricity to run. Most good radiant installers try to limit piping loops to below 300 feet.
There are many correct ways of installing in floor heat PEX within a slab. The best way is tying the PEX to the reinforcing mesh or rebar. When attaching the PEX PIPING to wire reinforcing mesh or rebar it is recommend that a zip tie be used every 2 feet of PEX Tubing.
Another way to install PEX in a slab is attaching the PEX piping to ridged insulation. The use of insulation screw clips or large plastic staples is common.
We recommend an insulation screw clip or staple every 2 feet if installing the tubing over insulation only (no wire mesh). If you use 2 Inch polystyrene insulation it is recommended that you use a 6 mil. polyethylene moisture barrier.
Installing the manifolds and keeping the lines under pressure (air or water pressure) for the concrete pour is highly recommended and required by code in many locations