What kind of heat the law requires
California requires adequate heating facilities, but it does not always require central heat — a permanent wall heater or built-in system can be acceptable, as long as it can actually keep the home reasonably warm and is safe.
The law focuses on whether the rental has heating facilities in good working order that can warm the unit to a livable temperature, not on a specific type of system. A built-in wall or baseboard heater may satisfy that. Relying on the tenant's own portable space heaters generally does not, because that shifts the landlord's duty onto the tenant.
If the provided heat cannot warm the home, its type does not really matter — it is still a problem the landlord must fix. What counts is whether the heat works and is safe. If your built-in heat cannot keep your home warm and your landlord will not address it, a free review can help.
This is general information about California tenant rights, not legal advice. Every situation is different.