You should do bit of detailed study into how radiators work to heat rooms. If you know the details, you can better communicate your need to the contractor. On the other hand you also understand their modes operand. Radiant heating works on very simple scientific principle that warm air rises. These are installed under the floor and radiate heat upward and outward, spreading warmth and comfort throughout the room. Hot water is circulated through the radiant floor system.
Get in touch with a good contractor. Ask your friends or relatives to recommend one if they know. Otherwise look into the advertisement. But before hiring know about their experience, certification and gather client feedback. An expert will have detailed idea about which components work well together, capacities of various systems, special considerations for installations in your area, and product warranties and reliability. He would do a room by room heat gain and loss calculation to decide the size of the system. There should be a team of contractors working in coordination -a concrete contractor, a general contractor, an architect, and a radiant system installer.