In Floor Hydronics

Hi all, I have built my home with in floor heating, using 1/2" pex, track mounted in a 1.5" Gypsum pour ... works great! ... But, a friend, has been told, as a top surface retrofit, to put down 3/8" pex between sleepers ~4" wide and to fill the pipe channels with thinset. This system was apparently designed and a book released, 1st ED, in the 90's by a P Eng name of "Yorkie". I question the heat transfer coefficient here and wonder if my friend is being dupped! Has anyone ever heard of this man, book or system and how well it performs? I haven't found a thing relating to any of it!
Thanks,
D of E

3/8" pex can't flow very much, so that will limit how much heat you could extract from it. That would be my first question. Intimate contact supplied by the thinset may help, but the metal distribution channels spread what is there much better. So, other than those thoughts, I can't help more, but I think there are probably better ways, and this one may not be able to provide the amount of heat you may require in Canada; depends on the house. There are distinct limits on how hot you can make the water for both comfort and the long-term health of the flooring material above it. Without the distribution plates, you'll need to probably run the water hotter, which generally also means lower efficiency.

Loop lengths with 3/8 need to be shorter than 1/2" and the system needs to be properly designed and installed but 3/8 will work just fine.

Jim, Pro or not, the logic of the "Yorkie" method Just didn't ring right with me either. What you are saying is how I feel about it. I understand an agree with Toms 3/8" statement as well, but the resultant heat distribution in my opinion will end up resembling a room full of hot railway tracks. Great for baby ckicks ... but humans? The retrofit is in a rejuvinated log home with 12" plank floors and no basement. I talked him into "Infloor" for his "New construction" shop and he loves it ... hence the desire to have the same in his house, but he trusts the installer, since it's the same guy that did the shop. He doesn't seem to understand that there is a big difference between a hydronically heated concrete pour and some surface tubes separated by essentially, what works out to be "wood insulation", when you look at the heat transfer rate. As I said, I have a Gypsum pour and I can often tell you where the start of the loops are, due to the temp (90 F). I figure he will have to run hotter than that! I just hope someone has heard of this "Yorkie" and can give me some "life experience" stories. Thanks for replying guys and I welcome any other comments.
D of E