IMC 803 closes with one of the most field-critical connector requirements: how close a hot chimney or vent connector can run to combustible construction.
Plain-English Highlights
Section 803.10.6 requires connectors to maintain the minimum clearance to combustibles set by Table 803.10.6. Key minimums include 18 inches for domestic electric and oil incinerators, 18 inches for domestic oil and solid-fuel appliances, 9 inches for oil appliances labeled for Type L venting, 18 inches for commercial and industrial low-heat oil and solid-fuel appliances, 36 inches for medium-heat oil and solid-fuel appliances, and a code-official-determined clearance for high-heat appliances.
The table is not always the final answer: if the appliance listing and labeling specifies a different connector clearance, the labeled clearance governs. Clearance reductions are permitted only in accordance with IMC 308. For plan review, the connector route has to be checked against wood studs and joists, roof and floor framing, combustible wall finishes, casework and shelving, stored materials, nearby equipment, and architectural framing details - a compliant appliance location does not automatically mean the connector route is compliant.
Why It Matters
Connector surfaces can operate at temperatures capable of heating nearby combustible materials over time. Insufficient clearance can lead to pyrolysis of wood and other combustibles, ignition and concealed fire, damage to finishes, unsafe field modifications, and failed inspections. Clearance is a three-dimensional requirement along the full connector path, not a single dimension checked once near the appliance.
Where To Show It
M-001: connector clearance criteria. M-101: connector routing and adjacent construction. M-501: clearance and protection details. M-601: appliance type and venting basis. A / S sheets: walls, framing, ceilings, and combustible construction.
Do
Identify the appliance classification first. - Apply Table 803.10.6 unless the appliance labeling requires otherwise. - Check clearances along the entire connector route. - Use IMC 308 when a reduced-clearance method is proposed.
Do Not
Assume 18 inches applies to every connector. - Measure clearance only at the appliance. - Reduce clearance with improvised sheet metal protection. - Ignore combustible framing hidden behind finishes.
Field Tip
Review the connector in plan and section. The most common conflict is not at the appliance - it is where the connector approaches framing, ceilings, walls, or other combustible construction before reaching the chimney or vent.
Masterbuild QA Lens
This closes the six-part IMC 803 Connectors series - sizing, location, dampers, construction, installation geometry, pass-through, and now clearance to combustibles all have to check out together before a connector route is field-ready. A connector that passes every other 803 requirement still fails if the clearance-to-combustibles table, or the appliance's own listed clearance, was never checked along the full route. See the IMC 803 series recap for the complete six-part checklist, and the IMC 804 series for direct-vent, integral-vent, and mechanical draft systems next.