Highly efficient Mini-split heatpumps are becoming simpler for the moderately technical homeowner to install everyday. 5-6 years ago installation typically involved a vacuum pump, a gauge set, sometimes a flaring tool to re-dress factory terminated line fittings, etc. Fairly inexpensive new 4th gen Mini-split heatpumps are drop-shipped from Amazon, have pre-evacuated line-sets that just bolt up to the inside head and pre-charged outside compressor units. I wonder how wide availability of these relatively cheap units are going to impact the bullish picture described in the WSJ article.