adding ducts
 

i have a laundry room on the back of my house and heat was never run there fr now i have an electric heater running so my water lines dont freeze again my question is can i run flex to the room and how far from the furnace do i need to be? furnace is in the same room probably12`*10 and also do i need a return

Welcome Bryon:
I would simply cut a 4" round or square hole in the plenum to supply the room and no return air duct is needed. That will keep an overpressure in the room in case there are some small hidden cracks and the positive pressure will keep the cold air from infiltrating.
Glenn