Your old toothbrush is the perfect scrubbing tool for removing rust from your metal heat registers. Tough but not abrasive, a toothbrush does the job no matter which type of household product you choose to remove the rust. Several household basic supplies will suffice for this job, so choose one based on what you have on hand. Start by removing the heat register. Put on a face mask to protect yourself against airborne rust particles. You're ready to put some teeth into this cleaning job using one of these methods.
Pour some baking soda into a bowl. Sprinkle it with some water and stir until the mixture forms a paste. Rub the paste on the heat register with the old toothbrush. Assess your progress periodically by rinsing the register. Apply more paste and scrub as necessary.
Place the heat register on an old towel. Sprinkle some salt over the rust stain, then drizzle some lime juice over the salt. Let the salty mixture sit on the stains for about three hours before scrubbing away the rust stains with the old toothbrush.
Try white vinegar to remove rust in one of three ways: Spray the rust with a half-and-half solution of white vinegar and water, make a paste with white vinegar and salt, or soak badly rusted heat registers in straight white vinegar overnight. Scrub the rust away with the toothbrush.
Choose steel wool or a fine-grit sandpaper as a last resort to remove rust from a heat register. Sand the rust in the direction of the grain to reduce the chance of making scratches on the register.