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How to Retrofit Radiant Heat From Above

This Old House plumbing and heating expert Richard Trethewey shares tips for installing new radiant-heat tubing on top of an old subfloor when there's no access from below

1. Fasten the plywood-backed radiant-heat panels to the subfloor with 1⅝-in. screws.
2. Stretch a continuous length of PEX tubing back and forth across the floor.
3. Use a rubber mallet to tap the tubing into the grooves of the radiant-heat panels.
4. Run the tubing ends down through the floor to the boiler.
5. Mount the manifold to a wall near the boiler, then connect the tubing ends to the manifold.
6. Run piping from the boiler to the manifold.
7. Install finish flooring over the tubing.


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