Advantages and Disadvantages of Hydronic Distribution Systems
One major advantage of hydronic heating systems is that they can be easily built into new energy-efficient homes. Efficiency can be increased by increasing the thermal mass of floor systems. Hydronic radiative systems may also be quieter than ducted heating, since there is no fan or blowing air. There may also be benefits to air quality, since heating ducts can develop mold and dust issues. Because water is an excellent conductor and relatively dense, hydronic systems require much less working fluid. This means that hydronic heating systems take up less room than ducted heating systems.
Some systems even allow differential room heating, in which residents can change the heat in any given room. This feature, of course, comes at a cost premium.
In well-designed systems, hydronic heating may be substantially more efficient than ducted heating. However, there is little data on this issue. It does seem likely that hydronic heating would be less power-intensive than other systems, as it doesn't rely extensively on fans. However, some systems may have a large pumping requirement, which reduces efficiency.
There are some disadvantages of hydronic systems. In the event of a retrofit, it may be probitively expensive to install a hydronic system. In addition, hydronic systems can typically only provide heat. This means that a separate AC system is required, increasing expense and space requirements. However, some homes may combine heating and cooling into a single hydronic system using a chiller boiler. This can be expensive, however.
One note: it is a misconception that hydronic heating systems prevent air dryness. They do not dry the air any more or less than a heating duct system.