Flexsul-seal vs. Thermo-Pex vs. whatever else

[2theHunt]

Does anyone have any experience (positive or negative) with Flexsul-seal. It is made by the makers of Insul-seal. I believe it is really their Insul-seal (insulated pipe) with two pex lines inside and then each end is capped off- which is supposed to trap dead air and almost double the R value. One of my concerns is that it appears that the supply and return lines are just lying inside the insulated core so that they are touching each other. Is it true that the return line may actually steal some of the heat directly from the supply line before it ever has a chance to reach my house. But if it is only a degree or two will that really matter? A couple positives are that it is much more flexible than Thermo-pex and about $4 per foot less expensive.

 

[jgrimm]

I looked at that product and ruled it out based on this chart: (broken link removed to http://www.flexsulseal.com/performance.php)

Unless I am figuring it wrong the 1" product loses 90.6 btu per 100' at 180 degrees/5gpm with a 10deg ambient. Add the loss for the return line and that is almost 11,000 btu/h lost just in the lines.