IMC 804 starts with appliance-specific venting systems where the manufacturer's instructions and listing are part of the design basis. The first plan-review question: is the appliance venting naturally, by forced draft, or through a listed direct-vent or integral-vent system?
Plain-English Highlights
IMC 804.1 requires vent terminals for direct-vent appliances to be installed in accordance with the manufacturer's instructions - the termination location, configuration, clearances, and installation method are controlled by the listed appliance system, not by a generic table. For plan review, verify the appliance model, the vent termination type, the manufacturer's instructions, the wall or roof termination location, and nearby openings and building features.
IMC 804.2 requires appliances incorporating integral venting to be installed in accordance with both their listing and the manufacturer's installation instructions - the appliance and integral venting system function as one listed assembly, and the vent configuration cannot be redesigned or field-modified without listing support.
IMC 804.2.1 sets terminal clearances for appliances with integral venting: natural draft requires a minimum 9 inches between vent terminals and a minimum 9 inches from openings through which combustion products could enter the building, while forced draft requires a minimum 12 inches between vent terminals and a minimum 12 inches from those same openings. Draft type directly affects the required clearance - the two numbers are not interchangeable.
Why It Matters
Poor terminal location can allow combustion products to recirculate or enter the building through nearby openings, which can create carbon monoxide exposure, nuisance shutdowns, poor appliance performance, exterior staining or corrosion, and failed inspections.
Where To Show It
M-001: venting basis and manufacturer requirements. M-101: appliance and termination location. M-501: wall / roof termination details. M-601: appliance model, draft type, and venting method.
Do
Identify the exact appliance and venting method. - Confirm whether the system is natural or forced draft. - Show the required terminal clearances. - Coordinate termination locations with architectural openings.
Do Not
Treat manufacturer instructions as optional. - Use the same clearance for natural and forced draft. - Locate terminals without checking nearby openings. - Field-modify an integral vent system without listing support.
Field Tip
Overlay the mechanical termination locations with the architectural elevations. If nearby doors, windows, louvers, or other openings are not shown, the terminal-clearance review is incomplete.
Masterbuild QA Lens
The draft-type distinction is the detail most likely to get missed on a fast plan-review pass: 9 inches for natural draft and 12 inches for forced draft look like a rounding difference, but applying the wrong one is a real code violation, not a conservative margin. Confirm draft type before checking the clearance dimension, not after. Next: Part 2 covers mechanical draft fundamentals - UL 378 listing, gas-tight positive-pressure venting, and automatic shutdown upon exhauster failure.