I am in the process of installing ductless mini-split heat pumps in my house, replacing my central HVAC.  My question is what to do about the heat duct system that I currently have and will no longer be used.  Is it sufficient go just seal off the heat vents in each room and to seal off the vent returns.  Someone suggested that i remove all the venting that is currently in my crawl space as this may allow leakage into my house.  But, will sealing off the vents and returns take care of this issue.  Will sealing off the vents and returns cause any problems that I may not be aware of?  Obviously, I’m not going to rip the vents out of my walls and rebuild.  Any info is appreciated.  Thanks.