Oh, those were from the Nixon administration years and were removed sometime during the Reagan administration while I was in the Navy overseas.
I guess we could say, Stone Age tech!
The important factor here is that the homeowners were so disappointed in the performance that they’ve never tried the newer technologies.
The efficiencies of then to now is significant so I can see how they might have been disappointed. I guess in 15 yrs mine will look like stone age but I have the peace of mind of saving a bunch on electric and would be little affected power-wise if the grid collapsed.