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If copper tubing is to be installed in a slab, certain precautions must be taken. If it is slab on grade, soil compaction is crucial. Flexing or cracks in the concrete can result in split tubing and leaks. The copper can be fixed in place with wire or tie straps to the re-enforcing wire or rods, but the steel and the copper must be grounded. The system must be a closed loop. Fresh water (hot water from a domestic hot water heater) will cause an electrolytic reaction between the chemicals in the concrete and the copper, eventually corroding and pitting the copper; creating plenty of leaks. If the slab is on top of wood joists, a double layer of 3/4" plywood is needed to keep the deck as rigid as possible.

Slab on Grade

After soil compaction, two inches of rigid insulation is recommended. The concrete re-enforcing mesh becomes a grid to fasten the tubing to with plastic tie straps or wire. At least 3/4' of concrete should cover the tubing to prevent weak spots that could collapse under heavy objects placed on the finished floor. If extremely heavy objects are to roll or sit on the floor, the deeper and more even the cover the better.

Slab on Slab

When pouring a new slab over an old one, rigid insulation is recommended even if the old slab has insulation under it. Efficiency and recovery time will be improved. Tubing can be attached to the mesh or to tracks designed to clip the tubing into. At least 3/4' of concrete should cover the tubing for floor strength.

Slab over wood

There are two ways to insulate the wood deck before pouring the slab over the tubing. Foil faced fiberglass insulation can be fitted into the floor joists directly under the deck, allowing a 2'' air space. The tubing is then stapled to the deck or fitted in the tracks manufactured specifically for the tubing. An alternate method is to lay rigid insulation on top of the deck. The fastening devices must reach through the insulation and into the wood to prevent the tubing from floating up as the concrete is poured.

Wood over Slab

If a wood floor is to be placed over a slab, sleepers are used to create a space between the wood and the slab deep enough to fit the tubing on top of rigid insulation. At least one inch of rigid is needed, and two is better. Wood has nearly the same R-value as insulation, and if the tubing is sandwiched between two materials of equal insulation values, it will lose heat equally in all directions, including the slab and into the soil below it.

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