Trane’s XR series central air conditioning units are Trane’s mid-model systems. These A/Cs offer efficiency up to 18 SEER and sound decibel ratings as low as 68 dBA. The XR series A/Cs are generally more efficient and quieter than Trane’s XB series entry level air conditioners. Trane has also added a new “briefcase” shaped unit, which works great for homes with space constraints.