Radiant floor heating systems that are used in concrete slabs are most often installed during the construction phase of a new building. The process of pouring a concrete basement floor is actually little changed from a traditional method.
The first step is the placing of an aggregate bed, just like in a traditional basement floor. On top of this is placed a 6 mil polyethylene vapor barrier. This is to prevent water vapor from entering through the concrete slab.
On top of the vapor barrier and along the foundation wall edges is placed a layer of insulation. This insulation ranges in thickness from 1" to 2". This is the most critical step in installing a radiant floor heating system. Any cool surface touching the concrete slab will try to steal the heat from it and the flexible tubing, thus lowering the heating capacity, efficiency and raising fuel costs.
Just like in a traditional concrete slab, a wire mesh is laid on top of the insulation. The difference is that now flexible tubing is looped on top of it. The flexible tubing is wire tied to the mesh. Spacing of the tubing is 6"- 18" depending on the climate and heat load. Tubing that runs in front of high heat loss areas such as doorways will need to be placed closer together. Interior areas can be spaced at wider distances.
The flexible tubing should be left in the bottom third of the concrete slab. This is to protect it from damage and to heat the entire concrete slab thoroughly. However, the tubing should not penetrate through the bottom of the basement floor slab.
Most flexible tubing should be run in lengths less than 400'. This is because the heat loss can be too great over that distance. Also greater lengths can cause too much resistance for a circulating pump and can shorten its life. If runs of tubing over 400' are needed, then additional loops should be added. Each loop is called a circuit. Circuits are controlled by a circuit manifold.
Before the concrete is poured for the basement floor, the flexible tubing must be pressure tested for any leaks. The tubing is pumped to 50 psi and left over night. If a gauge reads 5 psi or more lower, then a leak has occurred and must be repaired before pouring the slab. Air should be left in the tubing during the pour to help protect it and to determine if a leak has occurred during the pour.