When I got a set of your covers, I thought they might make a LITTLE difference. To my surprise, I have saved one entire oil fill this year. Considering what a cold winter we had, that makes it even more amazing. We also got one of your return covers. The back rooms of the house were always colder than the rest. Now all the rooms stay the same temperature. Installation is so easy. The whole house took about fifteen minutes. What a great product! I have recommended you to many of my friends.