Lined hole in floorboards

[Sarkles]

Hi, I was just wondering if anyone could please tell me what this is. I’ve pulled up the carpet in my son’s bedroom as we are having a new one fitted tomorrow and I’ve found this hole in the floorboards. It was covered with a piece of wood, it’s lined and it slopes down into a large plastic pipe. I can’t see anything inside but I’m not sure how far it goes.
I have no idea about DIY type things and I’m just curious about what it could be.
Thanks in advance to anyone who can help!

 

[JohnD]

should have been a metal grille.

looks like warm air heating
or air supply for stove or fire

what floor is it on?

is there a fireplace nearby?

how old is the house, and what size?

 

[Sarkles]

It’s on the first floor in a bedroom, not far away from a radiator but no fireplace/stove nearby. The house is approximately 40 years old, I think(!), 3 bedroom semi detached. It was just covered with a piece of wood when I pulled the carpet up.
Something to do with heating probably makes sense as the plastic pipe it leads down to disappears off under the floor.
Thank you for replying!

 

[Burnerman]

I’d guess there would be more of these warm air ducts elsewhere in the house......my first property had warm air heating, with small ducts fed off a larger, central one.
John