The edge strip is to reduce thermal bridging and also allow a modest amount of expansion for the screed. If you are paying £1500 for 35m2 you are being well ripped off! You need to bring the UFH slowly upto temperature or you will thermally shock the new screed resulting is a cracked / damaged...
The above posts are right the red panels are for a screed floor not a suspended floor. The maximum thickness of timber above any UFH system is 22mm. I have attached a typical cross section. The overlay is ok but should only be used on top of a floor as the overlay panels are not structural...
If you were using a wet UFH system you could use a system called RETRO18 which is a grooved fermacell board. The board is 18mm and if you insulate with SuperfoilUF (equivalent to a 40mm Celotex) the total additional height is 24mm. Output well over 75wm2
It does depend on the area you are trying to heat. You could fit a Danfoss FVH-R which is in effect a TRV on an UFH circuit. Size of area at most 15m2. This would run as if it was a radiator (on with the rest of the heating & using the boiler pump) and would connect to the rad system.
To rule out incorrect wiring undo the actuators so all circuits are open-loop. At this stage set the flow rates through each circuit between 1.5 & 2 lpm. Put one actuator back on and turn the stat off for that room - after a few minutes check the flow again to confirm the correct loop has...
UFH throughout - it is suitable floor all floor types / coverings. Much reduced running cost, no rads on walls (other than bathroom towel rails) - no issue with it in bedrooms. Far more comfortable & far easier to control.
If there is a chance of the units moving in the future then go under but make sure the customer is not storing food in the cupboard - or worse make sure the litter bin is not in the cupboard - chance of going smelly!!
Strictly speaking is the units are never likely to move - don't go under them.
The system I supply consists mainly of kit from Reliance in Worcester (RWC) - stainless steel manifolds, digital control. Pipe is PERT-AL-PERT - once bent it stays put. Then the method if installation is dependent on the floor structure; clip rails & staples for a solid floor and staples for the...