Danville’s summers are no joke. Sitting inland in the San Ramon Valley, sheltered from the marine layer that cools the Bay flatlands and Peninsula, the city regularly sees consecutive days above 95°F from June through September — and heat waves that push the thermometer past 105°F are not unusual. When a large Danville home’s aging single-stage AC system finally gave out last spring, the owners had a clear goal: never sweat through another summer.
We installed two Carrier 26TPA848W003 four-ton, two-stage air conditioners — one for each floor of the home — delivering up to 18.5 SEER2 efficiency and independent zone control throughout. Here’s how the project came together.
The Home and the Challenge
The property is a two-story Danville home in the 4,200 square foot range — a size common in the established neighborhoods east of Interstate 680, where homes built in the 1990s and early 2000s were designed with large footprints and separate upstairs and downstairs HVAC systems.
The original equipment — two aging single-stage units of the same era as the home — had been running on borrowed time. Both were operating well below their original efficiency, the upstairs system had developed refrigerant leaks, and a single-stage compressor simply cannot adapt to Danville’s wide daily temperature range: cool mornings in the mid-50s, mid-afternoon peaks pushing triple digits.
The owners wanted:
- Full replacement of both systems
- Meaningfully better efficiency to offset PG&E cooling costs
- More consistent temperatures throughout the day
- Equipment with a strong warranty and local service support
Equipment: Carrier 26TPA848W003
We specified the Carrier 26TPA848W003 for both systems — two units, both at four tons (48,000 BTU).
Why the 26TPA848W003?
4 tons is the right size. Each floor of this home — approximately 2,100 square feet — was sized through a simplified Manual J calculation accounting for Danville’s hotter climate zone, the home’s insulation level, window exposure, and ceiling height. Four tons per floor landed well within the correct range. Oversizing would have led to short-cycling: the unit blasts on, cools quickly, and shuts off — leaving humidity high and temperatures uneven.
Two-stage operation is exactly what inland Bay Area summers call for. The 26TPA848W003 runs at approximately 65% capacity during first-stage operation. On a 90°F Danville afternoon, the system runs in first stage the majority of the time — long, steady cycles that slowly pull both temperature and humidity down. It only ramps to full capacity during the hottest hours of the hottest days. The result is a home that feels noticeably more comfortable than what single-stage equipment delivers, with fewer abrupt temperature swings.
Up to 18.5 SEER2 efficiency. The SEER2 rating (the post-2023 DOE standard, which uses more realistic testing conditions than the old SEER scale) of up to 18.5 places this unit well above the minimum efficiency threshold required in California’s climate zones. The previous systems were operating at a fraction of their original 13-SEER nameplate rating. The efficiency upgrade alone meaningfully changes the monthly PG&E bill during June–September.
R-454B refrigerant. Like all current Carrier systems, the 26TPA848W003 uses R-454B — a lower global warming potential refrigerant compliant with the EPA’s AIM Act phasedown schedule. The homeowners specifically asked about refrigerant after reading about the industry-wide transition away from R-410A, and were glad to have equipment that’s fully forward-compatible with where regulations are heading.
Specifications at a Glance
| Specification | Detail |
|---|---|
| Model | Carrier 26TPA848W003 (×2) |
| Capacity | 4 tons / 48,000 BTU each |
| Efficiency | Up to 18.5 SEER2 |
| Compressor | Two-stage |
| Refrigerant | R-454B |
| Series | Performance |
| Units installed | 2 (one per floor/zone) |
Installation Overview
Day One: Removal and Rough-In
The crew started by recovering refrigerant from both old systems and removing the existing condensers, coils, and lineset where replacement was needed. The old outdoor units were located on opposite sides of the home — one on the north side of the house in a shaded equipment pad, one on the south-facing side with full afternoon sun exposure.
For the south-facing unit, we relocated the condenser pad to a shaded position around the corner of the home. Condenser units running in direct afternoon sun have to work against their own heat rejection, reducing efficiency and adding wear. The relocation added a short lineset run but will pay back in equipment longevity and performance over time.
Attic work included replacing both evaporator coils with matched Carrier coils, inspecting and sealing duct connections, and verifying that both air handler boxes were in sound condition. Both were — no ductwork replacement was required, which kept the project on schedule and within budget.
Day Two: Startup and Commissioning
Both condensers were set on new vibration isolation pads, leveled, and connected. Refrigerant lines were pressure-tested, evacuated, and charged to Carrier’s factory spec for the 26TPA848W003. Both systems were started and run through a full commissioning sequence: airflow measurement at each register, return air verification, thermostat calibration, and a staged cooling test on both floors simultaneously.
Upstairs reached set-point in first-stage operation during the morning commissioning — a good sign for how the system will perform on even the hottest days.
What the Homeowners Have Now
- Independent zone control — each floor operates on its own thermostat and schedule. The downstairs zone runs more during the day while the family is home; the upstairs zone ramps up in the evening when bedrooms are occupied.
- Quieter operation — two-stage units running at first stage are noticeably quieter than single-stage units at full blast. The upstairs bedrooms, in particular, benefit from the lower operating noise during nighttime cooling.
- Two-stage humidity control — longer cycles in first stage mean the evaporator coil stays cold longer each cycle, pulling more moisture from the air. This matters in Danville during the late-summer period when high-pressure systems push higher humidity into the valley.
- Up to 18.5 SEER2 efficiency — a substantial improvement over aging equipment running at a fraction of original spec.
- 10-year parts warranty with Carrier product registration, plus our own workmanship guarantee.
Danville’s Climate and Why Equipment Choice Matters
The San Ramon Valley — Danville, San Ramon, Alamo, Blackhawk — occupies a thermal pocket that heats up faster and stays hotter longer than cities closer to the Bay or the coastal range. The Diablo Range to the east blocks Pacific weather systems, and the valley floor can trap hot air during high-pressure events.
Average Danville summer highs run 88–95°F through July and August. Peak heat events regularly exceed 100°F. Air conditioning in Danville is not a luxury amenity — it is essential infrastructure for comfortable, safe living from approximately May through October.
For homes of this size, equipment that can modulate its output rather than simply blast on at full speed is the right tool for the climate. The 26TPA848W003’s two-stage operation is a meaningful match for what Danville’s summers actually demand.
Considering a System Replacement in Danville or the San Ramon Valley?
If your home is showing the same signs as this project — systems past 15 years old, refrigerant leaks, uneven cooling floor to floor, climbing summer PG&E bills — a proper load calculation and equipment consultation is the right starting point.
We serve Danville, Alamo, Blackhawk, San Ramon, Walnut Creek, Pleasant Hill, and all of Contra Costa County. As an authorized Carrier dealer, we handle sizing, installation, permits, and rebate processing.
Contact us for a free quote or call (510) 391-5597. You can also get a preliminary estimate for your home using our HVAC Installation Cost Estimator.
Also worth noting: the 2026 Carrier Spring Cool Cash promotion is currently active through May 31, 2026 — qualifying Performance-series installations like this one are eligible for instant rebates at the time of installation.