We live in a renovated 1925 built Colonial in NJ. I had to cut some hole into the kitchen ceiling, while planning the repair, I noticed that there is a cold draft passing between the ceiling the 2nd story floor. This also explains why the floor in the 2nd story is very cold, esp. in the bathroom which is above the kitchen.

Any idea where that could be coming from?

I thought that maybe the cold air comes up from the basement (yet cold air should travel down not up). Does insulated the bathroom floor help?
I also read a post that this is a good sign for air circulation, so I am hesitant do just insulate the space. But it feels strange to have an ice cold air drafting between your ceiling and floor and I winder what does to our heating bill.

I appreciate any ideas and information.