Warmer reservoir will hold less dissolved oxygen, its best to keep the nutes cool and the roots warm :)

I agree with Hex.

so.... how would you warm the roots if you're spraying cool nutrient water on them?

My nutes leave the tank at 55F-60F and the roots sit around 70F. Keeping the rootzone temperature in check is a higher priority for me as there`s no shortage of O2 with high pressure aero.