For Boulder City, the most energy-efficient air conditioners tend to be units with very high SEER ratings—preferably 16 or above. In recent years, the manufacturers Lennox, Daikin, and Trane have been some of the best brands in terms of offering high SEER, high-performing, and reliable central air systems. They have also tended to offer some of the best technologies in terms of inverters, which help central air systems run at a much more efficient level (i.e., save a lot more energy for the same amount of cooling). Still, when it comes to picking the best option for a specific household, it's always a good idea to consult with local HVAC pros.