The determining factor should always be the heat load when looking at distribution methods.
I'd say it is always best to heat the space, or meet the load, with the lowest possible supply temperatures. For that a 4" concrete slab, well insulated below and along the edges wins hands down. It is quite possible to produce 20 btu/ square foot in a 68F space with average fluid temperatures in the mid 90 F or a supply in the 100- 105F. Higher room loads would require higher supply temperatures. Tighter tube spacing 6 or 9" on center changes the required supply temperatures also.
Gyp, thin slabs will require a bit warmer supply, and they do not move heat laterally as well as a 4" concrete slab.
Adding aluminum transfer plates to bare pex tube does make a big difference. You need to get the energy from the tube to the load (floor). Aluminum being a great conductor does this, but also the conductive transfer of a wide plate opposed to a thin contact patch with bare tube stapled to the underside of the floor. look for a 15- 205 decrease in temperature with good heavy gauge transfer plates. Thin plates can be noisy "oil canning" is the sound you will hear as the plates expand and contract. use outdoor reset controls to minimize the wide temperature swings that lead to noisy plates, or bare pex for that matter.
UltraFin can and does work at lower supply temperatures. I have one system operating at 150F supply, powered by a mod con boiler.
A couple tricks... use PAP tube to minimize expansion movement of the tube. Run the tube parallel to the joist, two tubes per space UF staggered every 3' on the tube. UF does make clips to fasten tube without drilling across all the joists. There is a method to "thread" PAP through the holes at the joist ends if you go that route. If you have a high load area you can add some aluminum transfer plates with the UF. I did that on the great room which was all glass on one end. UF up until the last 4 feet then snapped into Radiant Engineering ThermoFins. A nice mix to cover higher loads.
The UF is a great way to add some radiant floor to an exisiting HW baseboard system. The higher temperature connects nicely to the UF without needing a mixing device.
UF is a joist bay heating system, driven mainly by convection. No question conduction transfer with a good conductor, like aluminum, or graphite
![Smile :) :)](/talk/styles/default/xenforo/smileys/grin.gif)
is a better way to move the energy.
The load, as I mentioned above, will help you determine the system and operating temperature required. For a residential application 27- 30 btu/ ft is a good guide for radiant. Above that look to supplement the radiant floor with baseboard or panel rads. Or better yet lower the load! The goal is to cover the load and keep the floor surface temperature in the 80- 83F temperature range. Above that it becomes uncomfortable to bare feet, especially on hard surface flooring, tile, concrete, etc.
I stay away from radiant under carpet and pad, regardless of the load, I feel it is a bad match.
I did infrared video tape the UF job I installed a few years back. I will say UF does provide a nice even heat spread across the floor. No stripping whatsoever, just a nice consistent even temperature spread.
hr