Well I thought I had this finalized, but now after speaking with the foam insulator I may change my mind. My EKO 40 is in a pole barn located about 130' downhill from the home which should be great. However, the plumber said I had to move the septic system drain field layout to where it blocked the most direct path to the new house. Additionally, the utility room in our final design ended up being on the opposite end of the basement with respect to the pole barn. I calculated about 200' (additional 70') to basically go around the septic drain field to the nearest corner of the walkout basement that would still be below grade. To run from the pole barn to the utility room it's more like 310' and figured the larger pex, longer distance, larger head circ, and more underground to foam insulate made it a no brainer to use the 200' option which would require additional piping in the basement ceiling to get the the utility room where the DHW & forced air furnace are located. Since the underground Pex on my install would be my "Primary Loop" and looped just inside the home (and also just inside the barn) the extra distance in the basement ceiling would not be an issue since a separate circs and loops would take it from that point the the DHW and furnace air handler. This corner of the basement is not the most desirable location for a piping junction since it will someday be a spare bedroom. It is too close to the window for me to put the closet which would be one way to hide the manifold, tees, etc. I guess I could give up a 12" of that wall when I frame around it but I would still need to put a small door or access panel should I ever need to reach the connections. The foam insulator shot me what I considered a great estimate ($500-600) to foam 2 1.25" or 4 1" lines this 200 ft distance. He wasn't too worried about whether it was 2 or 4 lines or $xx per foot but more like a flat charge for the job which has me leaning toward the 310' option which is much more straightforward. Heaterman helped me determine that on the 200' run that a single 1.25" or twin 1" lines would give me about the 11 GPM at 20* delta T 20 with ~22 ft head (110K BTU top load) but I want to check out the 310' option now also to see if it is viable. Can someone give the k values for 1", 1.25", and 1.5"? I was also confused about the whether the formula uses the actual ID values which are much smaller 1" is 0.8440-0.880, 1.25" is 1.034-1.074 per the ASTM spec for SDR9 pex. Would a single 1.5", twin 1.25", or 3 1" all be sufficient? Is the circ for this loop going to be a problem?