I have to travel from my hot water source/furnace through 30 feet of a 4 foot crawl space (new construction) to my tubing feed/return panel (which has four loops of 300 feet each). I can either go the shortest easiest route but it would necessitate using four 90 degree bends, or I can travel an additional 10 feet and make a large loop through the joists, and only have two 90 degree elbows in my 3/4 inch white flexible main feed and return lines. All input is appreciated. Question: Is it any worse (will it hamper flow) to use the elbows? Thank you so very very much for your time.

I believe elbows will hamper the flow a bit, however I'm not 100% sure.

Here is how I interpret your different options. Option A - 30 feet and 4 90 deg. bends OR Option B - 40 feet and 2 90 deg. bends. Also assuming that the 90's are PEX tube bends and not fittings. The table I used suggests that a 3/4" 90 deg bend needs to have a minimum bending radius of 7". The circumference of that circle would be (7*2*pi=43.98") so a 90 would be (43.98"/4=10.99"), lets say 11". So, Option A = 30' + (11"*4)=33.66 equivalent feet. Option B = 40 + (11"*2)=41.83 equivalent feet. Seems like Option A would be less restrictive. This changes a lot if you are using fittings. Here is the site that I used. Pages 6 & 12 seem to have the info you seek. I am not an engineer so grain of salt needed but don't think my analysis is too far off. Maybe the experts can set us both straight. http://www.toolbase.org/PDF/DesignGuides/PEX_Installation_Handbook_2006.pdf