IMC 803.10 moves from connector selection into actual installation. This is where support, horizontal length, chimney entry, and slope become field-critical.
Plain-English Highlights
IMC 803.10.1 requires connectors to be adequately supported, with joints secured by sheet metal screws, rivets, or other approved means - the connector should not rely on the appliance collar or chimney opening for support, since poor support can allow sagging, joint separation, loss of slope, or misalignment. IMC 803.10.2 limits the maximum horizontal length of a single-wall connector to 75% of the chimney or vent height; a 20-foot-high chimney, for example, allows a maximum 15-foot horizontal single-wall connector, since long horizontal runs increase resistance and can reduce draft.
IMC 803.10.3 requires the connector to extend to the inner face of the chimney or vent liner, but not beyond it - if the connector projects into the flue, it can restrict flow and collect deposits; for masonry chimneys, the connector must be cemented to the masonry in an approved manner, and removable thimbles must be permanently cemented in place with high-temperature cement. IMC 803.10.5 sets a minimum connector pitch of 1/4 inch per foot or 2% slope, rising continuously toward the chimney or vent.
Permit Proof Chain
Connector support method confirmed (independent support, not reliant on the appliance collar or chimney opening) -> joints checked for approved fastening -> horizontal length calculated against 75% of the actual chimney or vent height -> chimney or vent liner connection confirmed at the inner face, not projecting into the flue -> masonry cementing or thimble permanence confirmed where applicable -> continuous upward pitch of at least 1/4 in. per ft (2% slope) verified along the full run.
Where To Show It
M-001: connector installation criteria. M-101: connector route and horizontal length. M-501: supports, joints, thimble, liner connection, and slope details. M-601: appliance and connector sizing basis. Building sections: chimney height and connector elevation.
Do
Support the connector independently of the appliance collar or chimney opening. - Secure each joint with approved fasteners. - Check horizontal length against 75% of the actual chimney or vent height. - Terminate the connector at the inner face of the liner, and maintain continuous 1/4-in.-per-ft upward pitch.
Do Not
Allow unsupported connector runs. - Extend the connector into the flue passageway. - Ignore the 75% horizontal-length limitation. - Show flat or downward-sloping connector runs.
Masterbuild QA Lens
Improper support, excessive horizontal length, poor chimney entry, or inadequate pitch can create weak draft, condensation, soot or creosote accumulation, combustion product spillage, carbon monoxide risk, and failed inspections. Trace the connector in section and confirm four things together: support, horizontal length, liner connection, and continuous upward pitch. If any one of those four items is missing at a transition point, the installation is not fully reviewable.
Drawing / Submittal Check
Confirm the building section shows the chimney or vent height used to calculate the connector's 75% horizontal-length limit. Verify support locations, joint fastening, liner-connection depth, and pitch are all shown on the same detail rather than scattered across separate notes.
Common Review Risk
A connector detail shows a horizontal run without a stated chimney or vent height on the same sheet - the reviewer cannot verify the 75% limitation without cross-referencing a building section that may not even be included in the mechanical set.
When To Escalate
Escalate any connector detail lacking a stated chimney or vent height for the 75% length check, any masonry chimney connection without a documented cementing method, and any connector run shown without a clear, continuous upward pitch from appliance to chimney or vent.
Field Tip
Trace the connector in section. Confirm four things together: support, horizontal length, liner connection, and continuous upward pitch. If any of those are unclear, the installation is not fully reviewable.