/ Field knowledge · IMC 804
Name the category before you copy the clearance.
IMC 804: name the category before you copy a clearance. Direct-vent, integral-vent, and mechanical draft are not interchangeable details.
Educational 2024 IMC 804. Confirm adopted edition, IFGC if gas, and manufacturer instructions. This is not a termination design or a complete clearance table. Packet: 804 PDF · ES.
- Direct-vent (804.1): terminals follow the appliance manufacturer’s instructions.
- Integral-vent (804.2): listing and installation instructions. The 9-inch natural-draft and 12-inch forced-draft terminal clearances in 804.2.1 belong to that integral-vent context — they are not a universal direct-vent setback.
- Mechanical draft (804.3): UL 378 listing. Distinguish forced draft from induced draft. Portions under positive pressure need gas-tight construction listed for that pressure. Automatically fired appliances: interconnection that prevents operation when the exhauster is not operating. Manually fired appliances and fireplaces (804.3.8): different warning, backup-power, and smoke-detection controls.
- 804.3.6: a natural-draft appliance cannot connect on the discharge side of a mechanical flue exhauster. 804.3.7: size the exhauster and served vent from manufacturer instructions — nominal fan cfm is not a selection.
One clearance for every wall terminal
Overlay lot lines, adjacent buildings, walkways, doors, windows, gravity inlets, forced-air inlets, roof, grade, and meters/oil-tank vents. A plan-only horizontal measurement can miss “directly above.”
Source: DCT 804 · tool: vent category · 801: general venting.
What to send
The appliance listing (direct-vent vs Category IV vs mechanical draft), wall vs roof termination, and nearby intakes/windows/meters.
Free sample — the four-gate existing-chimney acceptance
“Existing chimney to remain” is the most expensive four words on a renovation mechanical set. The complete acceptance section from the IMC 2024 Chapter 8 Chimneys and Vents Field Guide — all four gates, the survey discipline, the escalation trigger, and the record it produces — is available as a free PDF. No email required. Download the sample (PDF). The full edition is available in the Field Guides catalog.
If the termination was copied from another job
Send the listing. MasterBuild will say whether this is 804.1, 804.2, or 804.3 — or a 9/12-inch integral-vent number got pasted onto a direct-vent appliance.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
MasterBuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval.