Where vent connectors for residential-type appliances are not installed in attics or other unconditioned spaces, connectors for listed appliances having draft hoods, appliances having draft hoods and equipped with listed conversion burners and Category I appliances shall be one of the following:
- Type B or L vent material;
- Galvanized sheet steel not less than 0.018 inch (0.46 mm) thick;
- Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 inch (0.69 mm) thick;
- Stainless steel sheet not less than 0.012 inch (0.31 mm) thick;
- Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Item 2, 3 or 4 above; or
- A listed vent connector.