Radiant under concrete floor?

you wouldn't want to do that because the heat would end up below the floor instead of in the living space.

if you came up with a way to fasten the aluminum heat transfer plates. That would work. Probably want 8 or more inches of insulation

8” concrete is about R 1.6 so about the same as 3/4 plywood with 5/8 hardwood.

But it will be a monster to control, a massive flywheel. Constant circulation and temperature modulation would be needed to help over shot and long ramp up

What type of structure with 8” concrete floors?

ChrisJ, could you be more definitive about what you are trying to do. I don't understand, I'm kinda on the dumb side.

This wasn't clean at all but I did a project adding snowmelt to an outside dining patio that was a suspended slab setup. we used joist trak plates screwed to the underside of the slab and insulated as best we could under the slab, and on the sides. It was completely out of normal install recommendations but it works even on our coldest, snowiest days. I forget what temp we ended up running the supply at, it was a bit of trial and error on that end. I think our slab was only about 4" thick though

Looking back one of the challenges was the joist trak being for 1/2" tubing, with so much load we had to keep the lengths to 150' approx. that portion had a 300,000 BTU/hr load, and I calculated a 162 supply temp, I think we settled on a little lower than that when all was said and done. that was for snowmelt so you should need a lower temperature. it will be very unresponsive though with that much slab between the tubing and the surface.

Floor warming is what I think he is after, the building has heat already.

Standing on cold concrete really saps energy from a person, besides being uncomfortable.

I just bough my first pair ever of heated socks for outdoor winter activity. They work great for old people with diminishing circulation :) Three temperature adjustments up to 8 hr on low setting before recharging.

I'd wear these in a shop with unheated concrete slabs.

maybe you would just constantly circulate 80-100f water through the tubing and let the slab get up to whatever temp felt comfortable over a couple days. might need all sorts of things if you're not heating it with a mod con.

What I didn't get was what the heat source that you were thinking about. How is the room heated, forced air, boiler, etc. What activity is on top of the slab. Perhaps, an insulated floor covering on top would make it more comfortable like engineered wood flooring with foam underlayment. I don't see how heating an 8" slab with possible edge loss can be done economically.

If it were a shop, for example you may be able to just put tube under areas where workers stand. No need to heat under machinery, toolboxes or benches for example.

Similar concept to just doing tire tracks in a driveway snowmelt instead of the entire driveway.

How about a suspended ceiling below the floor, with rolled out attic insulation on the ceiling tiles. Then Ultra-fin between the insulation and the concrete.

The answer is yes. But getting the heat to travel upward will require a significant amount of insulation below, and it's not a whole lot of fun to drill and pound in all the anchors over your head. I have done this 4 times now and the most memorable was a precast 8" garage floor over a theater room. I ran 1/2" tubing at 8" spacing with Joist-Trak extruded plates only 1" apart throughout (aside from the bends, obviously) and then 2" of closed cell followed by 2" of open cell foam sprayed directly to the underside. With 120* SWT we were able to squeeze about 24 BTU/SF through the slab and completely heat the garage with it. Another commercial space adding a storage room above a laundry room, we did the same 8" spacing and Joist-Trak but built a 4" soffit below and filled it with rockwool. That did surprisingly well also but was even less fun due to the Rockwool.

The only concern with overhead radiant tube is they are line of site, So you would not feel much heat sitting at a bench or desk, etc. Whereas the floor system would warm wherever you chose to place the tube.

A Hilti gun could shoot pins into the steel or concrete and just condiut clip the tube to the bottom of the steel that the concrete is poured on.

No need to add $$ transfer plates of you have the transfer plates already built in. You can also get a stud welder tool to attach threaded studs, to the metal decking.

I'd use a Pex Al Pex for more rigidity between clips.

The R-value of 8" concrete is about the same as 3/4 plywood with 5/8" hardwood flooring. The thermal mass "flywheel" effect could be mitigated with ODR.