Time To Replace Some Heat Pumps-Or At Least One

nm9stheham said, "Whatever you do, go for the highest SEER if you want to reduce costs." And he is absolutely correct. Just going to very high efficiency units should reduce operating costs about 40% from 1979 units.

Actually, spending $1000 to heat or cool a 4000 s.f. house is not that far out of line, even though Climate Zone 3 is relatively mild. PG&E has a very penalizing rate structure when you use a lot of kwhr per month. And now that they will have to pay for the forest fires, it is going to get worse.

So,
1. Get hi-eff units. New units will require that the contractor check the ducts for leakage.
2. Have tenants raise or lower (depending on season) thermostats by 2 or 3 degrees.
3. Have tenants try to live in one part of the house as much as possible, so one unit can be turned off.
4. Make sure you have at least 6" of attic insulation. Other home improvements are not really cost effective, unless there is a lot of single-pane glass.
Done.