Well, I never did that well in Fluid Mechanics, but I can say most things with heat exchangers relate to surface area...
Surface Area of tubing = PI * diameter * length in feet * 12in/ft
So, 50' of 1/4" = 3.14*.25*50*12 = 471 sq. in.
25' of 1/2" = 3.14*.5*25*12 = 471 sq. in.
When you...