IMC 803 covers the connection between the appliance and the chimney or vent. Across this six-part series, one theme stayed consistent: the connector must be sized, located, supported, constructed, routed, and protected as part of the venting system - not treated as an afterthought once the appliance and chimney are already placed.
Plain-English Summary
IMC 803.1 through 803.4 set the connector fundamentals: a connector is required unless the chimney or vent attaches directly to the appliance, the connector must stay within the appliance room except where 803.10.4 permits otherwise, single-wall pipe cannot be used through unheated spaces, the connector cannot be reduced below the appliance flue collar size, and branch connections must be coordinated with the vent manufacturer.
IMC 803.5 through 803.7 addressed dampers and multiple appliances: manual dampers are generally prohibited except for solid-fuel chimney connectors, automatic dampers for oil-fired heating appliances must be listed to UL 17 and installed per their listing, and where multiple connectors enter a common vent or chimney, the smaller connector enters at the higher level, subject to headroom and combustible clearances.
IMC 803.8 and 803.9 covered connector construction: vent connectors must be metal, and chimney connector thickness increases based on connector size and appliance heat classification under Tables 803.9(1) and 803.9(2). IMC 803.10.1 through 803.10.3 and 803.10.5 set the installation geometry: connectors must be properly supported, mechanically fastened at joints, within allowable horizontal length, connected to the inner face of the liner without projecting into the flue, and pitched upward at least 1/4 inch per foot.
IMC 803.10.4 addressed the connector pass-through: chimney connectors cannot pass through floors, ceilings, or fire-resistance-rated walls, and combustible-wall pass-throughs require a listed system or an approved Table 803.10.4 method - the clearance alone is not enough, the complete assembly matters. IMC 803.10.6 closed the series with clearances to combustibles: Table 803.10.6 sets connector clearances by appliance type and heat classification unless the appliance listing specifies otherwise, and clearance reductions are permitted only under IMC 308.
Why It Matters
Connector deficiencies can cause poor draft, condensation, combustion product spillage, overheating of combustibles, carbon monoxide exposure, fire risk, and failed inspections. A connector is a small-looking component with an outsized failure mode.
Permit-Set Checklist
Show the flue collar and connector size. Identify the connector material and thickness. Show the horizontal length and upward pitch. Detail the supports and joints. Coordinate manufacturer requirements. Show the pass-through method and clearance-to-combustibles basis for the full route.
Field Tip
Trace the connector from the appliance collar to the chimney or vent. If size, material, slope, support, pass-through, and combustible clearance cannot all be verified from the drawings, the installation is not fully reviewable - and it will come back as a field problem instead of a plan-review comment.
Masterbuild QA Lens
Most 803 rework does not come from missing a single requirement - it comes from checking each connector requirement in isolation instead of tracing the full connector as one continuous system, from flue collar to chimney or vent. Chapter 8 now moves from the connector to the venting method itself: the IMC 804 series covers direct-vent, integral-vent, and mechanical draft systems, where appliance listings, pressure conditions, and termination geometry take over as the controlling factors.