Equipment
- Two Carrier 19 SEER heat pumps (3-ton + 4-ton)
- Matched indoor air handlers
- New refrigerant linesets (R-410A)
- Google Nest 4th-generation thermostats (two zones)
- New condenser pads + line-set covers
- Updated electrical disconnects + surge protection
The starting situation
The homeowner had just bought the place and inherited two aging central air conditioners, one serving the downstairs zone, a second handling the upstairs. Both were single-stage units running on R-22, both well past the point where parts replacement made financial sense. PG&E summer bills had been creeping up year over year and the upstairs unit had started short-cycling on hot afternoons. They called for a quote on replacing the AC and asked what we thought about going further.
We walked them through the math on heat pumps. Two reasons it made sense for this specific house: the two-zone layout was already set up for parallel equipment (so we wouldn’t have to re-engineer the duct system), and the federal Inflation Reduction Act 25C tax credit gave us $2,000 in stackable rebate per qualifying heat pump install. Two heat pumps, $2,000 each: that turned the heat-pump path into the cheaper option after rebates, not just the more efficient one.
What we installed
- Two Carrier 19 SEER heat pumps: a 3-ton serving the downstairs zone, a 4-ton serving the upstairs. Both qualify for the IRA 25C federal credit.
- Matched indoor air handlers for each system, factory-charged on R-410A
- New refrigerant linesets: the old R-22 copper wasn’t worth pressure-testing for a thirty-year service life and you can’t legally top off R-22 anyway
- Two Google Nest 4th-generation thermostats: one per zone, heat-pump-aware staging configured at install so the system doesn’t crank resistance backup on mild evenings
- New composite condenser pads for both outdoor units, set level on compacted gravel
- Line-set covers on the outdoor refrigerant runs (the original copper had been left bare and was looking ugly against the stucco)
- Updated electrical disconnects with surge protection on the high-voltage side of each condenser
The detail that mattered
Two-system installs look like “do one, do the other,” but they’re not. The disconnects, the refrigerant lines, and the thermostat wiring for both systems share the same chase through the wall, touch one and you’re inside both. We staged it so that both old units came out the same morning, both new condensers went in on new pads by afternoon, and we did the lineset + electrical work as a single coordinated pass rather than two separate trips. That cut the customer’s no-AC window from a likely two days down to a single afternoon, and it kept the wall openings to one cycle of open-and-close instead of two.
If you’re getting bids on a multi-system install, ask whether the work is staged as one coordinated job or as two separate visits. The difference shows up in the wall finish and in how long you’re without cooling.
What the homeowner got
Both systems powered up the same evening, configured for heat-pump-priority operation with the Nest controllers. First summer test was the following week, temperatures hit the high 90s and both zones held setpoint without either unit having to stage up to its top compressor speed. That’s what you want to see: the 19 SEER capacity is sized comfortably for the load, not stretched.
Federal IRA 25C credit: $2,000 per qualifying heat pump, $4,000 total back at tax time. Equipment covered under 10-year parts and 10-year labor on our installation warranty, plus the Carrier factory equipment warranty.
The photos below show the finished outdoor condensers, the refrigerant-line work as we ran it, and the old AC units that came out at the start of the day.
Before
After
