For a myriad of reasons too long and embarrassing to go into, I need to redo my underground boiler piping, self-installed using the tried and true, sure to fail, and it did, method of wrap and stuff into a 4" drain tile. I've finally found an experienced, very accomodating, and reasonably priced closed-cell, spray-foam contractor, referred by past customers, who has used varying methods to do this. His current preferred method for my situation is to " leave the pipe in the tile and foam everything in place, in case you want/have to pull new lines, and the tile will be a last resort moisture barrier if the foam cracks, moves, etc." I need to say that we've discussed the closed-cell, lbs/cu.ft. density, etc., and he knows his stuff, and I know that this equates into more foam applied/money for him, but I have no problem with this if I get the best result. I'm not sure of the validity of his argument, from 2 points. First, even if I wanted to, in order for me to pull lines through I would have to for sure break loose and straighten-out 8 ft. of each end of the 4" tile to do this, and I'm thinking there goes the integrity of the continuous insulation covering. Second, maybe I would no longer have a 4" hot water pipe in the ground, but would for sure have a 4" hot AIR pipe, which is open on each end into the boiler room and house. My gut feel is that for best insulating, I would want the foam right at the tubing? The 4" tile would offer some last-ditch protection to the tubing, but is this needed, and would I give away btus for this? For me, I'm leaning towards doing my due-diligence to the trench and tubing preparation, get rid of the drain tile, and foam around the tubing only. I think the likeliehood of having to put in new tubing is pretty remote, and if I ever had to, I would just dig up and replace as needed. What do you think? Thanks!