What flooring works best for radiant heat?

Concrete, perhaps with stain, paint or epoxy. Or ceramic tile.

Any floor will work, I like Tile/stone best, slab work, our RHT floor panel system delivers water at a very low temperature effectively on a platform type radiant system.The broader question is what type of building are you doing? slab on grade with perimeter foundation, platform with topping pour? Platform with floor panel system?
This is a start point.
Dan

I appreciate your information. We have designed it to be slab and now that we have had the Geo-test for soil and water we have just found out that the slab will work well.

if it's a slab floor with geo heat, follow JonR's advice if you can and you'll really milk the geo for every bit of COP you can. good stuff.

What is JonR's advise and what is COP? I am sorry for all the questions but I am a novice trying to learn.

I found JonR's advise but still not familiar with COP thanks

COP is "coefficient of production" and it's a measure of how effective heat pumps (like geo units) are at delivering heat.

COP of 3 would mean for every watt the heat pump uses, you got 3 watts of heat. higher is better.

Thanks!

I think Rob means "coefficient of performance" = COP

basically the lower the water temp the more efficient the geo will operate. The most efficient would be bare concrete then thin set tile. A design I'm working on right now in northern IL has supply temp to main floor of 96* return of 87* which will then be used to supply garage and garden basement which will return to heat pump at around 82. all floors are concrete some stained and stamped some just stained...Eric