While I have only scratched the surface on the riveting subject of duct leakage, I hope that this will motivate some readers to take steps toward making their heating and air systems more energy efficient. But it is generally accepted that the vents and ducts should be cleaned twice a year. https://Www.chinaleatheroid.com/redirect.php?url=http://[email protected]/ox/shogo/ONEE/g_book/g_book.cgi