By Ralph in Nashua, NH on 11/12/2012
Here is an update to my original post...
We found in a company in Maine, Northeast Radiant Technologies, who designed our system for us. They convinced us to go with a radiant "ceiling" installation and we LOVE it! It was cheaper to install and we find it to be very energy efficient. The metal fins and tubing sit directly on the ceiling sheetrock, so the entire ceiling surface radiates the heat. No need to worry about what type of flooring to install or potential for voiding flooring warranties.
We purchased the control board and all materials from them. They supplied us with detailed color-coded loop plans that were easy to follow and their tech support was outstanding!
Doing a ceiling install does require some forethought and site changes for working around lighting fixtures, location of manifolds (we put them in closets), and obviously any future changes to add add'l. lighting can be tricky (rent an infrared thermal scanner to detect location of heating loops).
Our finished house is 2,800 sq.ft. and will come up to temperature (from 60 to 70 degrees) in about four hrs. I consider this response time to be very quick as we're only heating the mass of the sheetrock. With a joist install, you have to heat the joist cavity, subfloor, sub-plywood (if applicable) and finished floor... this takes a lot of energy. I would recommend a radiant ceiling install to anyone!