What do you call the method of using water under cement floors in home construction to help with heating?

Question

I went to a home that had this and I want to do more research on it, anyone know what it is called/ where i can get more info

Answer 1

This is called hydronic radiant floor heating.  

The Romans used a variant called "hypocaust" which used hot air under the floor.   Some systems also use electric radiant floor heating.

Answer 2

radiant heat.