The launch poll

A water-heater question every shop has argued at the counter, put to living shops. Tallies are banked as dated attestation data: a poll moves a claim's shop-lane weight by +2 at most, and never counts as an outcome.

You swap a water heater on a closed system. The expansion tank goes in:

Every swap — no debate

Only with a PRV or check valve in the line

Only when the AHJ requires it

After I check the pressure — it depends on the house

Vote

Reference only. Compiled from the cited official sources as of the date shown; adoptions and rules change. Confirm with the authority having jurisdiction before designing or permitting work.