Burning smell through vents after 20 min drive

GKB

I agree with the check for an oil leak idea. This seems to be the most common source of burning smells in cars. The smell is distinct, and I can only describe it as an acrid smell. It fits with the description you gave of starting after 20 min. of driving as the engine would be good and hot by then. It takes only a small leak usually from some upper portion of the engine and takes only a small amount of oil getting on the exhaust manifold/s to make the acrid burning oil smell. Good luck finding it if that is the cause.