Calling all radiant heat experts

Solid_Fuel_Man

I was speaking with a homeowner and he wants to put radiant over an existing slab for a finished basement. He wants to put down 1" XPS, and router in grooves for 1/2" pex and put aluminum foil.....tin foil....theb a thin cement board over that with flooring over the top. 

I was telling him the aluminum foil was pointless as it's so thin that I didn't believe the conduction wouldn't spread the heat out enough to make a difference. 

Hestloss is very low as the space stays at 60 as it is now without and finish work. I have not run any numbers, space is roughly 20x30. All concrete 6' below grade. 

I know @hot_rod did some experiments like this and gather some real world data on what a system like this would emit at given water temperatures. 

hot_rod

if it is a low load as we expect the foil may be adequate. Some of the wood dry systems have that thin foil adhered to the wood panels. Not so much fun to work over.

Or you could use the aluminum transfer plates over the foam for better transfer and more $$. The Thermofin U plates work well for that.

Or the Viega climate panels over the foam.

Grooving that foam will be messy

What type of flooring?

A floating engineered wood flooring would work, and be the thinnest option, over the Viega Climatepanels or Uponor brand.

I like the Roth System also, a heavier gauge aluminum, continuous aluminum. Glue them down and snap in the tube. Not a lot of R value, but for a basement?? Maybe Roth over 3/4 foamboard for more R.

https://radiantdesignandsupply.com/productsthermofin

Solid_Fuel_Man

I'm not doing any of this, we were just having a conversation. I actually suggested the Roth or Warmboard but he was turned off by the price. 

I told him I would at least put plates in between sleepers over his 1" of XPS.  I'd consider yhe 1" to be a little on the thin side as well. But I haven't seen this and all he told me is that he has a newer oil boiler with 3 zones and baseboard. So a high temp system now. 

Tinman

I can’t see any pro putting their reputation on the line for that. 

hot_rod

Solid_Fuel_Man said:

I'm not doing any of this, we were just having a conversation. I actually suggested the Roth or Warmboard but he was turned off by the price. 

I told him I would at least put plates in between sleepers over his 1" of XPS.  I'd consider yhe 1" to be a little on the thin side as well. But I haven't seen this and all he told me is that he has a newer oil boiler with 3 zones and baseboard. So a high temp system now. 

I've know people to buy rolls of aluminum flashing from the lumber store and hammer out their own plates, if he is a DIYer looking to save $$

I knew a guy that home made aluminum plates like that to go over a rubber tube system to increase output. The rubber tube doesn't move and squeak like pex can in thin plates with crappy grip.

Solid_Fuel_Man

@Steve Minnich I completly agree. I told him I didn't think it would work...but it may due to the low heat requirement in the space. However it was actually just a conversation I had with him at a supply house. I told him he can do what he wants. But it's not something I'd put my name of for sure.

GroundUp

I sure wouldn't want to spend any time on something like that, he'll have a heck of a mess and probably a lot of broken foam by the time that's complete and for minimal output with only 1/4" of foam below the tube. Is the idea just for supplemental heat or does he want a warm floor? Is a radiant wall or ceiling maybe an option?