Why Proper AC Unit Sizing Matters for Comfort, Efficiency, and System Longevity Proper AC Unit Sizing Matters for Comfort. This article started with a simple conversation, and a very common assumption. A friend was telling me about a new AC installation at his home and explained that even though the space only required a certain size unit, he chose to double it to be safe. His logic made sense on the surface. In reality, it’s exactly how many comfort and moisture problems beg