Space-Age (Radiant) Heat

It's the middle of summer, so I won't appreciate the benefit right away, but radiant heat was the next major project on the agenda, as it must be done before any flooring can be installed.  New floors meant moving everything out of the house and into the garage.  Here's my makeshift bedroom out there.

First up is a layer of R-5 foam board insulation, so that the heat travels upwards into the room instead of out through the foundation.  Note the holes one foot on-center.  Those holes become support columns for the radiant layer once it is poured.  The insulation had to be glued down with foamboard adhesive to prevent it from floating back up during the pour.

Next, I used a router to cut grooves in the insulation.  The grooves help hold the tubing in-place and reduce the total height of the final assembly, keeping my floors from growing too tall.

The radiant tubing is PEX, a slightly-flexible but very-durable plastic tubing.  Unlike copper, it has a bit of give to it and is less likely to be damaged by expansion or contraction in the concrete.  It also costs considerably less than copper, making it a good choice for a modern hydronic radiant system.  The tubing is held down with special foam-board staples.  Each room gets its own heating loop.  The winding path of the tubing gives the water more distance to transmit heat to the floor, and the close spacing makes good use of the entire floor as a heating surface.

All of the radiant loops come together in the utility closet, just under the high-efficiency hybrid water heater.  The green unit includes an integrated heat exchanger, circulator pumps, and control unit.  The hydronic heating loop is kept separate from domestic hot water so that there is no risk of contamination to the potable water supply, but gets the heat indirectly through the heat exchanger.  The gray object is an expansion tank that keeps the pressure steady across temperature variations.  Attached to the control unit is a radiant manifold.  Each heating loop connects to both ends of the radiant manifold, which provides flow meters and balancing valves.  Air gaps, pressure and temperature gauges, a pressure relief valve, and a fill/drain valve round out the setup.  As you can see, it's quite a lot of stuff to have crammed into such a small space.

Once the tubing was all laid out, it was time for another inspection, followed by ordering the pour.  The material used here is GypCrete 2000, a gypsum-based cement-like product.  Some guys show up with a truck and do the whole house in a day, for a reasonable fee.  The GypCrete is hard enough to walk on within a day, but it needs about a month to dry completely.  The GypCrete also serves to level the floors, providing a good surface for final flooring installation.

After the drying time had elapsed, I sealed the GypCrete with the supplied sealer, which rolls on much like a paint.  Firing up the radiant heat loop, all I hear is the faint hum of pump motors and the water heater firing.  The radiant heat is configured to operate as the primary heating source, with the forced-air system serving as a backup on really cold days, or if a quicker temperature change is needed.  I look forward to trying it out more-extensively this winter!