Im installing 1/2" pex for radaint heat under my floor . This is new construction so floor joises are open. the floor joises are TGI . I have 2 floors 1600 sq. ft. a floor with 9 cielings on 1st floor and 8 ft. cielings on 2nd. My question is should i hang the pex 3 inches or so off the bottom of the floor with hangers or use the alum. heat shealds to strap it directley to  the bottom of the floor? pro's and con's? I plan to use the double bubble foil insulation, should it be installed as close to the pex as possible or at the bottom of the joise creating a cavity?  I currentley have 1500 ft of radaint pex installed in the basement floor under concreat.   Hot water Heat supplied by a 250,000 btu outside central boiler corn/pellet stove.