IMC 803 starts with the basic requirements for connecting an appliance to a chimney or vent. The connector must be properly located, sized, and coordinated with the appliance and vent system before any of the material, installation, or clearance requirements later in the section matter.
Plain-English Highlights
IMC 803.1 requires a connector between the appliance and the vertical chimney or vent, unless the chimney or vent attaches directly to the appliance - the drawings should distinguish the appliance flue collar, the connector, the vertical chimney or vent, and any direct connection.
IMC 803.2 requires the connector to remain entirely within the room containing the appliance, except for a compliant wall pass-through under IMC 803.10.4; where a connector passes through an unheated space it cannot be single-wall pipe, since rapid heat loss there can reduce draft and increase condensation or deposit buildup.
IMC 803.3 sets minimum sizing: the connector cannot be smaller than the appliance flue collar, and where an appliance has multiple flue outlets with no specific manufacturer instructions, the common connector area must equal or exceed the combined outlet area - a requirement based on area, not just diameter. IMC 803.4 requires branch connections to comply with the vent manufacturer's instructions; fitting type, connection geometry, and assembly method should not be left to field judgment.
Permit Proof Chain
Appliance flue collar identified and sized -> connector confirmed to remain within the appliance room or routed through an approved 803.10.4 pass-through -> connector size checked against the flue collar (or combined outlet area for multiple outlets) -> branch fittings and connection geometry matched to the vent manufacturer's instructions -> a continuous, documented path shown from appliance outlet to the vertical chimney or vent.
Where To Show It
M-001: connector criteria and manufacturer notes. M-101: appliance location and connector route. M-501: branch, pass-through, and chimney connection details. M-601: flue collar and connector sizes. A / LS sheets: room boundaries, walls, shafts, and rated assemblies.
Do
Show the complete connector route from appliance collar to the vertical chimney or vent. - Keep the connector within the appliance room unless a compliant IMC 803.10.4 pass-through applies. - Match or exceed the appliance flue collar area, including combined area for multiple outlets. - Coordinate branch fittings and connection geometry with the vent manufacturer's instructions.
Do Not
Reduce the connector below the appliance outlet size. - Run single-wall pipe through an unheated space. - Combine multiple flue outlets into one connector without checking total area against the manufacturer's instructions. - Leave branch geometry or fitting selection to field discretion.
Masterbuild QA Lens
Most 803.1-803.4 rework does not come from a single missed dimension - it comes from the connector route never being traced start to finish before submittal. Before the set goes out, confirm the flue collar size, the connector size, the room boundary the connector stays inside of, and the manufacturer basis for any branch fitting, all on the same sheet set a field inspector will actually walk.
Drawing / Submittal Check
Compare the appliance schedule's flue collar size against the connector size shown on the mechanical drawings. Confirm the connector route stays within the appliance room (or cites the IMC 803.10.4 pass-through detail if it does not), and confirm any branch fitting is called out with its manufacturer basis rather than a generic fitting note.
Common Review Risk
A connector schedule shows a size that matches the appliance nameplate diameter but does not account for a second flue outlet on the same appliance - the combined outlet area exceeds the connector's actual area even though the diameter check alone looked correct.
When To Escalate
Escalate any appliance with multiple flue outlets and no manufacturer instruction for combined connector sizing, any connector routed through an unheated space without single-wall/double-wall confirmation, and any branch connection whose fitting basis is not documented by the vent manufacturer.
Field Tip
Trace the connector from the appliance collar to the vertical vent before signing off on the sheet. If its location, size, branch fittings, and manufacturer basis are unclear from the drawings alone, the design is not yet complete, regardless of how finished the rest of the set looks.