Gas and Oil Home Heating Furnaces - Looking for info on older Luxaire furnace

We have an old Luxaire oil furnace, maybe from the 70's of so.
When I first used the furnace there was a vent on the wall with a switch, however I noticed that the wall got pretty warn sending out hot air from the vent. I wasn't sure what this was, so I turned off the switch and now the vent and the wall area remain cold.
I thought it was a heat holding vent becausse after the furnace shut off this vent kept letting off warm air and kept the house pretty warm. Without this being on I noticed the house cools off pretty fast.
Does anyone have any idea how this system works? When I had the furnace inspected I forgot to ask about it because at this time we had it turned off.
The furnace is in the basement and the vent is above and over about six feet from where the furnace is located. The area to where I should see a furnace duct going into it is covered over with boards so I can't see what's under it..but I can see there is a wide duct type shape leading into it.
What I don't understand is to how the switch is able to turn off the heat retention in the wall area.
Please if you have any info could you share.
Thanks

I'm fairly familiar with the Luxaire's of that era. If you could provide some pictures of the furnace, duct work, switch, etc. I might be able to figure something out. You can post pics on photobucket.com or similar photo hosting site & provide a link here.

Thank you for responding.
I will send you the pictures.
~ B