What one historical example does—and does not—say
Trane’s 2012 guide for listed Convertible Air Handler models describes secondary drainage as backup for blocked primary drainage, a float-switch option, and an auxiliary-pan recommendation for horizontal installation. This historical model-family example makes no universal requirement or substitute menu, confirms no current model or code, states no switch response, and guarantees no protection from water damage. Trane, Installer’s Guide 18-GE08D1-10, pp. 7–9 (2012).
Make the quote and handoff specific
Ask the proposal to list each proposed safeguard as included, excluded, or unresolved. For each, request its stated purpose, fit for the identified model and orientation, and intended response, if any. Ask who confirms applicability, including any local requirement for the responsible professional to check. If documentation or a site condition remains unknown, record the open question and who will resolve it before authorizing related work.
At completion, request a written record of what was included, what model-specific documentation or verification was used, and any open item with its follow-up owner. Do not open equipment, handle water or wiring, or test or alter components yourself. This guide cannot determine your home’s design or diagnose a problem.