Depending on where you live, your weather, type of home construction, etc. hydronic heating heating can bee a great way to go. Rod, is a little bit off on hydronic. First, go on the web and look up KITEC pipe or WARMRITE. KITEC pipe is a composite pipe. It is used extensively in hydronic heating, is flexible like soft copper, stays where you put it, is better insulating than copper, carries a 30 guaranty on the pipe and fittings, and can be used in a retrofit situation. Depending on the criteria above, you might be able to use a regular hot water heater for the system. If you are in a colder climate, you most likely will need a boiler, and closer pipe spacing. There is a gentleman at KITEC pipe in Denver named Mark Bauer who will design the system for you. You need to provide Mark with the floorplans, door and window sizing, climate, type of insulation, etc.. He will tell you how many loops to use, what size pipe and boiler, and even draw out a piping layout plan.
I am a salesman in the plumbing system in Southern California. If you have any other questions on this, please e-mail me directly.