In Floor Heat In Efficient Homes. | Construction and DIY projects | Forums

Pex in the slab or not...this was something I struggled with a lot for our project...we have decided not to do it...for several reasons which include issues with necessity, time, and money.

Below there is a link about radiant floor heating in well insulated homes. It is a bit dated, 2002, but it makes good points. I think the 'Final Thoughts' section sums it up well. 

"Final Thoughts
It’s hard to express doubts about something that’s really popular. Like ground-source heat pumps, radiant-floor heating has a loyal and zealous following of builders, designers, and homeowners who consider it to be the best heating option around—and appropriate in almost any situation.

One of the reasons radiant-floor heating is so popular is that it is so much more comfortable than what most of us have experience with: older, drafty houses where there is significant floor-to-ceiling temperature stratification. If more people realized that the same—or at least a similar—level of comfort could be achieved simply by creating a really well-insulated, tight building envelope, we could be keeping a lot of people extremely comfortable while also saving a huge amount of energy, without needing radiant-floor heat. “A house with a good enough envelope to be called green—well-insulated and tight—will have a very high level of comfort no matter what type of heating system is used,” says Shapiro, “as long as that heating system is well designed.”

From:

http://www.oregon.go.....diant.aspx