PRRT with heater

Hi

I am now in the process of modifying my K – series cooling system. I have bought a PRRT and will be mounting this. I also have a heater that I need to be able to use, as it gets quite chilly over here in Norway. Would it be fine to leave all the original bypass hoses that goes to the heater with the PRRT mod? I have seen some refereces to some people running both the normal bypass and the PRRT bypass. Or would the twin bypass system rob to much flow out of the radiator?

Kristoffer