Yesterday, Chris and Justin from CRS Mechanical started stapling down the 1/2″ diameter PEX tubing that is a key element of the hydronic heating system. The tubing will be embedded in 3″ of concrete, which in my case will form the finished floor. The tubing is stapled down first; then #2 rebar is laid over it; then the concrete is poured. The staple-down phase goes pretty quickly with the right tools (a spindle for uncoiling the tubing so it doesn’t twist, and a pneumatic stapler that has a special nose that centers the staple over the tube.

This kind of heating system is often called “radiant heat.” My college heat transfer professor would roll over in his grave to hear that description. This would better be called “convective heat.” The warm water/glycol solution heats the concrete via forced convection (pumping warm fluid from the boiler) and then the concrete heats the air via natural convection. Very little of the heat transfer is via radiation. Radiation is the transfer of heat via infrared waves, as in what you feel if you put your hand under a heat lamp, or for that matter, the way you are warmed by the sun. The transfer of heat via radiation is minimal at the temperature of the floor in a typical hydronic heating system.