Radiant Design Revisited

Since the excitement of the new floor is out of the way, time to go back and talk about the actual layout of the oxygen barrier Pex used in the radiant floor.

Radiant Layout with Zones

Radiant Layout with Zones

The references and calculations used to design the pex layout were explained in previous posts. (Intro to Radiant, Manual J, and Uponor Design Manual)

Most of the materials for the radiant floor and heating system (and plumbing) were ordered from Pex Supply. The floor pipe is Uponor/Wirsbo Oxygen Barrier Pex A hePex plus in 1/2″ size. I decided to order 2 1000 foot coils in order to have plenty and to ensure long enough runs without any breaks underground. Turns out that made sense for this install.

There was one change in the pipe configuration from the original plan, There are four types of pipe layout, based on heat loss expected in the room due to outside walls. If you look closely at the zone plan above, all of the types are used depending on the exposure to the on-grade outside walls. This plan is more sophisticated and hopefully will provide better coverage than the original plan that was almost all single wall layout.

Radiant Pipe Layout Types

Radiant Pipe Layout Types from the Design Manual

Although difficult to see in the drawings, the final layout has two rows of pipe against the outside walls that are only 6″ apart and the first run of pipe in all zones is routed as directly as possible to the outside walls.

Sweet Home 3D Pex Layout

Sweet Home 3D Pex Layout

The drawing and layout for the pipes was superimposed on the architect’s floor plan using Sweet Home 3D software, a very useful and FREE home design tool in Mac, as well as Windows and Linux formats. The software allows for mounting an image in the background to draw changes into. I imported the architect’s floor plan jgp and then aligned the scale to the program by entering the measurement of one wall. That means that the scale was altered at least twice from the original drawing, once to make the jpg and the next time in the import and superimposed scale. The resulting measurements could only be approximate, no matter how hard I tried to be accurate with them.

Using this program’s measuring tool, each of the total runs was supposed to be shorter than 300′. In practice two of them were a little longer. That is why it was good that the pex I was working with was long enough that the longer lengths could be cut and still avoid under slab connections. Unfortunately the long rolls also gave us fits during the initial installation!


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