Floor system: flat panel or ashlar panel?

If you try to search on web you will find many pictures related to the underfloor heating system. In most cases these are systems made with the use of an insulating panel with knuckles, also called ashlar:

But in some cases, however, the application of a flat type insulating panel can be observed:

The questions arise spontaneously:

• Why are these two types of insulating panels on the market?
• When is it better to use the first solution and when the second?
• Which is the panel that allows you to have a better performance than your floor system?

Having worked for many years in the plant engineering sector, the answer that is almost always given to me is the following:

"It depends on the habits of the installer of the system; some installers are better off with ashlar because the knuckles help and speed up the laying of the pipes (which fit easily between the knuckles); others prefer flat panel insulation, such as the clips for fixing the pipes are easy to apply and you have more freedom in laying the pipe. "

These reasons are also true and no one could dispute them. But the most logical explanation for the existence of the two types of panels is the following:

The images refer to a floor system schematized for the same house: on the left with the ashlar panel and on the right with the flat panel. The ashlar one constrains the laying directions of the pipes: that is, according to the orthogonal directions or at the limit according to the only possible inclined direction ... the 45° one! In the case of rooms with an irregular perimeter, as in the example above (left image), the presence of knuckles in some areas requires the installation of so-called "zig-zag" pipes. Conversely, the use of a flat panel (right image) allows you to lay pipes much more regular and rational.

Instead, let's look at the following image:

In the case of rooms characterized by the orthogonality of the walls, the use of an ashlar panel or a flat panel is indifferent.

Therefore my advice is the following: with rooms characterized by non-orthogonal walls it is preferable to use the flat insulating panel; with rooms characterized by orthogonality both solutions are valid. The existence of the two types on the market is motivated by the different layout configurations that a house can have.

But we still have to answer the last question: which is the panel that allows us to have better performance than our floor system?

The hot water circulating in the pipes heats the screed and the latter transfers the thermal energy to the room to be heated. The knuckles are made of insulating material and therefore, even if in a very small part, hinder the transfer of energy between the pipes and the screed that covers them. For this reason, with the same temperature of the water circulating in the pipes and with the same thickness of the overlying screed, the thermal output will be greater with a flat panel than with a knuckle panel. ATTENTION: we are talking about a really minimal difference in thermal output, I would say almost negligible!

Therefore my advice is the following: motivate the choice of the insulating panel based exclusively on the layout of the house and forget the difference in thermal output because it is really insignificant.

 Please note. Source of some images: web