New duct in basement bathroom
I have a framed in bathroom in my basement that I need to add a heat duct in. The bathroom is directly beside the furnace. The rectangular vent heating the north side of the home runs through the top of the new bathroom. Can I tap directly into this in order to add heat to this new bathroom? There are no other runs within 6 feet of this but it is within 3 feet of the furnace. Also, if this is OK to tap into, can I cut into the side of the rectangulat venting to add a new run or do I have to go from the top as the rest of the home is done?
The house is a 1200 sq foot rancher on the main floor and the basement is of equal size. All of the other rooms in the basement already have heat vents (5 total).
Thanks!