3 phase units in an older home, adding a unit?
We have purchased a 4400 square foot single level 1960s ranch home in Phoenix. The home is cooled and heated with 2 units with 3 phase compressors that will need to be replaced soon. Our inspector told us to seriously consider replacing the existing units with 3 phase units because they are more efficient and last longer even though they are more expensive. We are also hoping to add a unit or two to the house, so that we can keep different areas of the house at different temperatures.
We have 3 units in our current 2700 sq.ft. house and we really like being able to heat and cool just certain portions of the house, specifically the master bedroom separately. We use programable thermostats and keep living areas warmer at night when we are sleeping etc.
How difficult is it to add another unit using existing duct work? Is it relatively straight-forward? Is there a downside?
And, should we go with 3 phase compressors? We are going to talk to our HVAC people, of course, but I like to have a clue :)