Radiant systems do not heat by forcing warm air through vents like normal forced air systems. Instead radiant heat works naturally by warming the closest objects from the heat source, which is why they are usually placed under floors. With a properly installed radiant system your feet will no longer freeze in the winter and the warmth will be consistent from the adults down to the young children and pets.
A boiler is the heat source for radiant systems. Top of the line boilers are state of the art using cast aluminum heat exchangers as opposed to cast iron resulting in higher AFUE ratings which means better efficiency and lower utility bills.
*Note: though radiant heat systems can offer extreme comfort and efficiency, there are many things like proper installation, components and insulation that if not done correctly can cause a radiant install to suffer.