How to Install Hot Water Radiant Heat

Hot water radiant heat is an efficient, quiet and comfortable way to heat your home or commercial building. Hot water is piped through tubing installed in the floor, which is most often a concrete slab. As the floor warms, it radiates heat upward into the room. A boiler, solar water heater or even a hot water heater heats the water. A small pump pushes the heated water through each closed loop. Valves and thermostats control each heating zone.

Tubing Installation

Install Hot Water Radiant Heat
  1. Plan the order of your work according to zoning diagrams. Draw a piping schematic for each zone. Water is hottest when it first leaves the heating supply and coolest on its return. Begin each zone along an exterior wall, which loses the most heat.

  2. Leave enough extra length at the beginning end of the tubing to connect to the manifold. Lay the tubing with 6-inch spacing between runs. Keep spacing even to ensure you do not have cold spots in the floor. Follow the piping schematic, unrolling the piping carefully. Tie the tubing to reinforcing steel in the slab using zip ties, or clip to under-slab insulation. Do not kink the tubing or bend it at sharp angles.

  3. Leave enough extra tubing at the end of each line to connect to the return manifold. Cover the ends of the pipe with tape or other covering to protect them from the concrete. Pour the concrete slab.

Connect to Hot Water Supply

  1. Connect the supply and return lines from each zone to the supply and return manifolds. Install zone control valves on the return lines. Connect the supply line to the supply side of the boiler. Connect the return line to an expansion tank and recirculation pump. Connect the recirculation pump to the return side of the boiler.

  2. Install an automatic vent valve at the highest point of the piping system. Install a 30 psi automatic pressure relief valve in the system for safety.

  3. Install two boiler taps with a ball control valve between them at a convenient point in the piping system. This is used to charge the system with propylene glycol and distilled water mix.

  4. Hook up the electronic controls for the system, following the manufacturer's wiring diagrams.

Charging the System

  1. Attach one rubber hose to each boiler tap. Close the ball valve between the taps. Attach the end of one hose to the output side of the charging pump. Put the end of the other hose into a 5-gallon pail. Attach one end of the third hose to the inlet of the charge pump and place the other end into the 5-gallon pail. Fill the pail with propylene glycol mixed with distilled water.

  2. Open both taps and run the pump. Continue adding fluid to the pail, keeping both hoses covered. Allow the pump to run until you no longer see bubbles in the bucket.

  3. Close the boiler tap that goes to the 5-gallon pail. Allow the charging system to bring the pressure up to 15 to 20 psi. Close the second boiler tap. Turn off the charging pump. Open the ball valve between the boiler taps.


  • While charging the system, zone control valves must be manually set to the open position.
  • Check local building codes to see whether state or local government requires electrical or plumbing work to be done by a licensed electrician or plumber.

About the Author

Lisa Jensen grows organic food and lives in an adobe house that she built. She teaches aikido, is an experienced back-country skier and backpacker and is active in her community. A graduate of the University of Calgary, Jensen writes about gardening, home projects, social sciences and sports and recreation.