Radiant Heat
The idea of radiant heat is a fairly simplistic one. If one hot object is placed next to another object (let's say a cup full of hot coffee placed on a table), then the heat will transfer from the hotter object to the cooler object. This is the concept behind radiant heat water pipes. If water is heated, and that hot water is run through pipes in the walls/floor/ceiling of a room, then the heat from the pipes will radiate into the room and heat first the objects, and then the air. While this system tends to work best when installed in a floor, it's not unusual for people to use radiant water pipes in a ceiling.
Installation
When radiant heat water pipes are installed in a ceiling, there are a variety of steps that have to be taken. First the pipes must be installed so that they run through joists (or they're bracketed to joists) for support. Additionally, the pipes are often connected to panels which interlock to create a sort of heating grid. With systems in a two story hours, the pipes could be sandwiched between two layers of panels so that it's a ceiling heating system for the ground floor, and a floor heating system for the second floor. The entire assembly has to be supported, and the floor/ceiling joists must provide that support.
Drawbacks
Radiant heat water pipes that go through the ceiling may not be the best bet for many homeowners. Because heat rises, the radiant heat must be enough that it reaches down to heat a room, which requires a bigger output of energy. Additionally, pipes in the ceiling have to be run up through the walls as well, whereas pipes in the floor requires less pipe to run the water, and their support is easier to take care of. Lastly, radiant heat water pipes in the ceiling will be almost completely ineffective in rooms with high ceilings, or in domed ceilings.
Tags: water pipes, heat water pipes, , radiant heat water, Additionally pipes, ceiling heating