I found the formula for calculating pump needs, GPM = BHTU / (Load factor density of liquid) X Temp Drop
So with an estimated temperature drop of 40F, and the density of Propylene Glycol at 40F = 436. I get 17,440, that divided into an expected 80 btu/hr = 0.0125 GPM. or 3/4 gal an hour... soo...