Turn off the heat in your home at least five hours before engaging in this project. This is to ensure that the vent is completely cool.
Sand the surface of the vent with low-grit sandpaper. This will help to roughen up the surface, making the paint better adhere to the vent.
Clean the surface of the floor vent with a mixture of 1/4 degreaser and 3/4 warm water and clean cloths. Dry the vent with dry, clean cloths.
Add painter's tape to the floor around the floor vent. Lay two side-by-side strips of 2-inch painter's tape on the floor around each side of the vent.
Apply the oil-based paint to the vent with a handheld paintbrush, using slow, even strokes.