San Lorenzo Furnace Repair
done today, done right.

California licenses this trade as a C-20 — warm-air heating, ventilating and air-conditioning. In the Contractors State License Board register for Alameda County, 4 active C-20 licences give a San Lorenzo business address as of 2026-09-02, out of 260 across the county. That is a thin local bench. Expect a San Lorenzo job to be run by a crew based a few minutes away rather than one with a San Lorenzo address — for a same-day callout, drive time matters more than the pin on the map.

Unusually, every one of them holds the C-20 on its own, with no general-building licence beside it. These are heating-and-air shops, not remodellers who also do furnaces.

By business structure the San Lorenzo list runs 2 corporations, 2 sole owners. No single structure dominates, so what turns up varies with who takes the call.

Those addresses sit in a single ZIP: 94580 — and we cover it.

CSLB issues licence numbers in sequence, so the register doubles as a record of how long the trade has been established here. The longest-held active C-20 in San Lorenzo is number 915348; its newest is 1152130. Across the whole county the range runs 68847 to 1159177, so San Lorenzo's oldest surviving licence sits well up it: every active licence in San Lorenzo was issued after most of the county's were, so the local trade here is newer than its neighbours'.

That register is how we decide who gets your request: an active, unexpired licence, and a preference for the C-20-only shops. 2 of the San Lorenzo licences come up for renewal before the end of 2026, and a lapsed licence is uninsurable — one more reason to check the number rather than the van. Check ours, or anyone's, yourself — every California licence is public at the CSLB licence lookup. A contractor who will not give you a licence number has told you what you need to know.