A $1,500 water heater swap shows what too-low bids can hide

The plumber wrote that the job called for a 50-gallon forced-draft heater. The winning installer set a 40-gallon natural-draft unit instead, removed the direct vent and ran single-wall aluminum pipe tight against wiring, and the house now smells of burning plastic. That account is his. The code shows what such a swap demands.

A power-vent heater uses a fan to push cooled exhaust out, often through plastic pipe in a side wall. An atmospheric heater depends on hot gas rising from its draft hood through metal pipe into a vertical vent or chimney. The International Fuel Gas Code allows plastic vent pipe only on appliances listed for it, and it bars connecting natural-draft vent connectors to any part of a positive-pressure mechanical draft system. So the old wall termination cannot serve the new heater. When a new appliance is hooked up to a vent or chimney already in place, section 501.15 requires resizing it as needed to give the appliance the draft it needs.

Then there is clearance. The code's connector table sets 6 inches between single-wall metal pipe and combustible material for listed draft-hood appliances, and Rheem's installation manual repeats the figure. Single-wall connectors may not pass through walls, floors or ceilings, must rise at least 1/4 inch per foot toward the vent and must be Type B where they cross attics or crawl spaces. Aluminum connectors are allowed only in 1100 or 3003 alloy sheet at least 0.027 inch thick. The draft hood's relief opening needs 6 inches from any surface.

Rheem tells installers to run a spillage test at the draft hood after five minutes of burner operation: a match flame or smoke should be drawn into the opening. When bids are far apart, compare the tank size and vent type against the spec, check that the quote names the vent material, and ask whether a change of heater type includes a new vent.