In a hydronic slab on grade installation - radiant tubing is attached to re-bar or 6x6 wire re-mesh with plastic ties and embedded in cement.  In residential installations, a 4 inch slab is typical.  Tubing can be installed in the lower half of the slab - spacing and height will vary by design.  Slab insulation is recommended, but not always necessary.   The large thermal mass stabilizes temperature fluctuations, but can slow the response time.  This is a very cost effective radiant installation method and is highly recommended whenever a cement slab is being poured.

In a hydronic topping slab installation - radiant tubing is installed on top of an existing slab or sub floor with wire mesh, plastic clips or a track system.  A thin cement slab is poured over the piping.  The typical thickness is 1 1/2" although other thicknesses are certainly possible.   This method is useful in retrofits over existing slabs, sub floors, and also post-tensioned slabs.

A hydronic overlay normally uses a 1 x 4 sleeper, although a 5/8 x 4 sleeper would work for 1/2" PEX. The sleepers are attached to a slab or sub floor and radiant tubing is installed between the sleepers with or without metal plates.   Heat transfer plates enhance the evenness of the heat and accelerate the output.  They may also add significantly to the overall costs.

Hydronic systems can be installed with grooved subfloor boards and pre-manufactured panels.  These are normally installed on an existing sub floor or slab - the pre-manufactured panels can also be used as the structural sub floor.    Aluminum heat transfer plates help these systems heat rapidly and spread the heat evenly.  Typical spacing is 12" on center, but may vary with design.

In a hydronic staple-up system the radiant piping is attached to the underside of the sub floor by way of staples, j-hooks or metal plates.  Insulation is recommended, but not always necessary.   A good rule of thumb would be 3-4 times the r-value below the tubing as above.  R-values are cumulative, so if you have a sub floor with floor coverings that have a cumulative r-value of 3 - you should have at least r-9 to r-12 below your radiant tubing.   Staple-up systems may need to run at a higher temperature, it will depend on your radiant designer.   This method is often used in retrofits where joists are accessible as well as many new construction project.  The benefits are a low materials cost - it is however a more labor intensive installation.

A hydronic suspended system is similar to a staple-up system, however the tubing is not attached directly to the sub floor.  It may be stapled to the sides of the joists or suspended from the sub floor.   This installation method is often used in retrofits - including projects where access from below is limited.  Hanging systems generally run at a higher operating temperature and because they heat the joist cavity - the heat above is very even. The materials costs are normally low - but this can be a labor intensive installation method.