 He says, if you put a pile of dirt in your hand, you could take a torch and put a flame to that dirt. And for a short time, your hand's not going to feel it. You're not going to get hurt. The dirt will not transfer the heat to your hand. So he said the smallest amount of dirt on these outdoor coils will keep it from being able to get rid of the heat you're attempting to extract out of your home and reject it to the outside air.