Hi there, I just stumbled across you site, and man do I wish I had seen this a few years ago. Very informative, and very well laid out. Short story first - I designed my first radiant system, and in slab on grade system for a 32 x 40' pole barn (would become my cabinet shop) 5 years ago. It works beautifully. I should mention that I am a mechanical engineer, specializing in air flow and temperature control systems - helps to understand the physics of heat transfer and fluid mechanics.
Fast forward two years, we built a 2300 sf log home, and decided to go radiant with it. My only experiences prior to this were my parents house (1700 sf ranch) and my previously mentioned pole barn. I purchased a system from Radiant Floor Company, and to make a really long story really short, it didn't work well at all. So bad that the following year, I ripped every last component out that they sold me (7/8 tubing, thin transfer plates, foil radiant barrier, Takagi instantaneous heater, more) and installed a system of my own design (1/2 tubing, Zurn xfer plates, foil backed bubble insulation, triangle tube prestige boiler with a DHW holding tank, etc). Bottom line, it works very well (for a poorly insulated house).
Now to my question. I am interested in finishing the basement this winter. At the recommendation of Radiant Floor Company, I didn't add heat to the basement when we built (stupid me) and now have a very cold basement. When redoing the heating system, I did build in an additional zone to use in the basement. Looking at my options, I can either do baseboard, or radiant tubing above the slab. I have the ceiling height (9' superior wall foundation) and as such, am thinking I want to go ahead with the radiant above slab. My question - I did not insulate the floor before pouring, and as such, it is quite cold (46°F). Should I insulate under the subfloor, or should the tubing lay directly on the concrete for more thermal mass? I plan on using 5/8 or ¾ sleepers, along with a subfloor. I have the room to lay 1 or 1 ½" EPS foam down under the sleepers if necessary. One other question if I may, do you recommend the sleepers to be closely spaced to the tubing (ex, 8" sleepers on 9" centers) or should I allow air space around them (ex, 2 - 4" sleepers on 9" centers)? The advantage (as I see it) of tightly spaced is the ability to use a thinner subfloor, the advantage of further spaced is less material for the sleepers).
Other info that may be of use, we live in western NY. The foundation is insulated with R12.5 EPS and an additional R13 fiberglass. I am planning on insulating at least a portion of the floor joists for the upstairs for sound dampening. The basement is very dry, with the exception of a condensation issue in the summer (which hopefully will be alleviated by insulating the floor).
I apologize if you don't answer these types of questions, just looking for recommendations. I have spoken with several local installers and sales people, who only want to recommend the system they sell. Thank you for any insight you could provide.