You might say the coil is the other, less visible part of your system. While a coil may be a component that you're not very familiar with, it's just as important to your home's comfort as your air conditioner. And, because the coil was designed to work in tandem with your outdoor unit and furnace, it's important that they match in both size and capacity A matched system gives you maximum performance and efficiency. And, that's where Trane comes in. Your older non matched system may be leaving you with your system unbalanced with less efficiency and higher than necessary uiltity bills.