San Carlos, CA: the heat pump payback math
San Carlos technically pencils out, but only past the point the equipment would need replacing anyway. Against a like-for-like gas furnace and AC swap, going electric costs $1,000 more up front here (already netting out a $2,000 tax credit). Lower bills claw that back: about $8 saved annually, for a payback of roughly 128.7 years. San Carlos's own numbers say this pencils out only in theory, not in practice.
The climate behind San Carlos's payback figure
2349 heating degree days pile up here every year, so San Carlos has a mild winter by US standards; the cooling side runs to 335 cooling degree days, where summers add a moderate cooling load. The 99% winter design temperature here — the cold snap equipment must be sized for, not the seasonal average — is 39.2°F, against a record low of 37.4°F. That puts the seasonal coefficient of performance at 3.37 for the recommended standard unit. A standard ducted system is enough here; San Carlos's design temperature doesn't justify the cold-climate premium. Climate figures trace to the nearest NOAA station, SAN CARLOS AIRPORT, 1.6 miles from San Carlos.
San Carlos's running-cost comparison, in dollars
A 2000-square-foot house here would pull roughly 1,765 heating kilowatt-hours annually on top of cooling, totalling about $673 a year on electricity. San Carlos's gas rate of 22.01 per Mcf, applied to the 24 Mcf a year the furnace burns, puts its running cost near $681 a year, against 32.83¢ per kWh for electricity. Looked at as a full purchase rather than an incremental one, payback here is roughly 1415.3 years, leaving the 15-year total $883 behind.
If your home heats with electric baseboard instead of gas
Not every home in San Carlos has gas service. Swap the comparison to resistance heat instead of gas, and San Carlos's answer improves. The saving here runs about $1,422 a year, which recovers the extra $5,500 spent going electric in roughly 3.9 years.
San Carlos against the rest of the country
Among 3206 cities, San Carlos's winter puts it at rank 2253 for severity, while its size puts it at rank 1370 for population — 1 in both cases being the extreme. That's the mildest third of cities covered, where utility rates carry more of the answer than climate does.
Deciding what's next in San Carlos, CA
About 29,403 people live in San Carlos, California, and every number on this page is what a contractor would actually work from when quoting a system here — the point isn't to replace that quote, it's to tell you whether to bother asking for one. Here, there's no cost penalty to waiting until your current furnace or AC actually needs replacing.
Ask a local HVAC contractor for a quote before committing either way.
More on how this number was built
The methodology guide walks through exactly how San Carlos's 3.37 seasonal COP and the rest of this page's numbers get built. San Carlos's case is the "pays back too slowly to count" kind covered in the guide to cities where the math never really works.