steel wool and foam to plug holes to prevent mice

Had an issue where the little buggers used the heating duct for the FW tank to access the furnace and built nests in it and the duck work. Had to replace all the duct work, clean and sanitize the heat exchanger box and then added 1/4" hardware cloth to the 3" duct feeding the FW tank compartment. The urine smell was overwhelming till the bleach did its' job. Find where they are getting in and stop them!!!