The question we are asked most on site walks. The answer depends on three numbers and one fact about your ducts.
The three numbers
- Design temperature. Santa Clara’s winter design temperature is about 38°F. A modern inverter heat pump delivers nearly its full rating at that point, so the “heat pumps do not work in the cold” story is a Minnesota story.
- Panel capacity. A ducted heat pump needs a 30–40A circuit. Most 1960s 100A panels can take it; some cannot without load management. We check before we quote.
- Duct leakage. A heat pump moves more air at a lower temperature than a furnace. On ducts leaking 30%, it will feel weak. On sealed ducts it is the steadier of the two.
Where a furnace still wins
- You have a sound furnace under ten years old. Keep it, add a heat pump as dual fuel, let the controls choose.
- No room outside for a condenser and no attic for an air handler.
- A very large home with a 400A service that is already fully used.
What we actually recommend
For most Santa Clara homes replacing both furnace and AC, a ducted variable-speed heat pump, with the ducts tested first. Incentives from the utility and the federal credit are handled by us. Terms through our lending partner are set after the site visit, never before.