Hello, I'm new here and quite virgin to radiant floor heating. Just bought a new house.(1982 model that needs a lot of work) I'd love to finish the basement and install radiant floor heating. My last house we put down drycore and gave up on any floor based heating system. Air ducts worked ok. Are there ways to do this? At a fairly low cost that is... I don't really want to jack hammer the floor out and replace it. Unless it can be done cheaply. Thanks for all replies.

This is a guess - others will have much better ideas. Glue or nail down 1/2" hardibacker but leave gaps where you can mortar in 3/8" PEX. Cover with plastic and then a flooring suitable for basements. Or put down foam first and use wood plus the typical aluminum plates. Or just bury PEX in a 3/4" concrete overlay (which will crack, but cover it).

Radiant built into in an uninsulated slab is hugely inefficient due to losses to the earth.

Going with a radiant ceiling instead, and putting at least R3 (half-inch XPS) under a finish-floor for comfort & mold-control can be nearly as cushy for much less work.

There are several radiant floor systems made for installation over an existing slab. Since the loads are quite, "hugely" may be a bit of an exaggeration. Back-in-the-day, we installed many radiant floor systems without the obvious benefit of rigid foam insulation.

Back in the day fuel was a lot cheaper too, eh? The losses depend a bit on the moisture content of the soil, the deep subsoil temps, etc, but yeah "huge" losses aren't likely in absolute terms, but it'll still most likely be a double-digit fraction of the heating energy for those rooms to do it as uninsulated radiant slab rather than radiant ceiling.

Soil is insulation. So with the edges well insulated and no ground water flowing nearby, there is ultimately no where for significant heat to exit "the system". Yes, this is an exaggeration in the other direction and it does take some initial energy to heat the soil in the expanded idea of "the system".

The cost of doing the soil & water table analysis to demonstrate that the soil at any particular site could be used as insulation is usually more than adding R10 of foam and being done with it, eh? ;-)

You're both right!