I'm new here -- signed up to get some advice on upgrading heat pumps -- my home has 2 heat pumps (upstairs / downstairs) I think one is a 2 Ton and the other is a 3 Ton.

We had the house built in '92 so these units are 16 years old -- brand is Lennox and they are 11 SEER.

I'm interested in replacing with 16 SEER -- questions:
(BTW this will all be done by an A/C contractor)

1) What needs replacing besides the base unit?
2) Can I replace just one unit (I'm thinking the downstairs unit, at least) and get some energy savings? It seems to run the most.
3) What about switching the 2 ton with the 3 ton, and getting a new 16 SEER 3 ton -- can this work?

Our kwh rates here in Houston are going thru the roof (looks like the average is $.16-18 right now!) -- want to see if we can do anything to fight back.

Please advise.