[playpaukes]

I opened a vent cover in my spare room and there's nothing underneath it. No ducts, nothing but insulation and the ground. I live in a mobile home. Why is this? lol How come nothing is there?

 

[Windows on Wash]

Doesn't make any sense. Unless there is a combustion device in there that was specified to get more make up air, there would be no reason to have it.

 

[WhatRnsdownhill]

at one time there may have been duct work hooked up to it from underneath , but removed sometime ago..

 

[dd57chevy]

Maybe the previous owner removed the ductwork . If it is a "spare room" , maybe they used it for storage & thought it would conserve energy & make the rest of the home warmer .

You'll probably have to crawl under the home & take a peek .