Stretch wrote:

... If you installed a slightly oversized 2 stage heat pump, it would run
in low stage all summer providing about 65% total cooling capacity. Then
it would run in high stage (High Capacity) during heating season when
it was below 45 degrees outside. You could possibly set back in this case...

That makes sense. Then again heat strips have their place. It isn't hard to
think of a situation where they would save money (assuming net.thought.police
still allow thinking), eg in a house with lots of heat loss and little thermal
mass and a wimpy heat pump, eg 1000 Btu/h-F and 1000 Btu/F and a (70-30)1000
= 40K Btu/h heat pump on a 30 F night. If the heat pump can only keep up with
a 40 F temp diff, no setback is possible, so a 10 hour night requires 400K Btu
of heat, or 200K Btu of electrical energy with a COP of 2. With heat strips,
the house can be 50 F most of the night, with 100K Btu of heat pump electrical
energy and 1000Btu/F(70-50) = 20K Btu of 8 AM strip energy, so the strips save
80K Btu, ie 23 kWH of electrical energy, and the low-cap heat pump is cheaper.

a two stage heat pump usually adds about $2,000.00 to an average installation.

Why not a single-speed compressor with low and high airflows?

Nick