I have oil heat, with forced air.. We have, what we believe to be, is an air intake vent on the floor.. no heat comes out so we think it just pulls air in. Can I put a sofa over it? There is like an inch or two of clearance from the bottom of the sofa to the floor.
As long as there is a couple of inches clearance under your sofa, it will be fine. The vent is likely a cold air return that lets cooler air along the floor be directed to the furnace room where it can be reintroduced into the system to be reheated. It is important that it not be blocked with a rug because the room would become slightly pressurized causing the forced air furnace to work harder and be less efficient.
You can buy a plastic extension that has magnets on it that will stick to vents, then it extends out to the edge of the couch, since it is clear you don't notice it. It;s made for heating but would probably work for the return duct too.
Putting the sofa over the intake may hinder the intake a bit, but as long as it is not blocked completely, air is getting in, so I think you are fine.
