I have a 1969 house in SE Minnesota. The slabs for the basement and one of the ground level rooms were poured over the in floor ventilation. In the ground floor room especially there is cold air coming out of the vents when the heater runs. It is a corner room and basically un-usable in the winter. The ventilation first splits at the furnace and one part goes straight into the ground and runs along the basement wall at the front of the house. It then wraps back at some point and goes up a half level to the ground floor room that I first mentioned.
There is no crawl space to get at the ventilation so I don't think it can be repaired or insulated without digging under the house. What I would like to know is if it would be practical to just block up the ventilation running under the slab at the source and just install baseboard heat for those rooms? The basement is finished but it is also not that big and I was thinking for a more efficient fix to actually reroute the vent to go in the ceiling of the basement.
Does anyone have any ideas that are maybe more creative than this? I have no experience in this field so I probably don't know about a lot of other solutions.