IMC 801.8 covers a step that's easy to overlook on replacement and renovation work: when an appliance is removed, relocated, or converted, its old chimney or vent opening doesn't take care of itself. It has to be closed by an approved method.
Plain-English Highlights
Abandoned inlet openings in chimneys and vents must be closed by an approved method. This comes up constantly on existing-building work: appliance replacement, boiler or furnace removal, water heater relocation, conversion from chimney venting to direct vent, conversion from fuel-fired to electric equipment, and demolition of old vent connectors all leave openings that need to be addressed - not just left as-is because the appliance is gone.
Permit Proof Chain
Identify every appliance being removed, replaced, or relocated -> trace its existing connector and chimney/vent inlet opening -> confirm whether the chimney/vent remains in service for another appliance -> specify an approved closure method and material -> verify the closure is compatible with the chimney/vent system.
Where To Show It
M-001: demolition and vent abandonment notes. M-101: existing appliance, chimney, and vent locations. M-501: abandoned opening closure detail. M-601: appliance replacement schedule and venting basis. A/LS sheets: rated walls, shafts, chimney enclosures. P sheets: water heater, boiler, fuel, and oil coordination.
**Do** - Identify every abandoned chimney or vent opening on the drawings, not just the new appliance's vent. - Show connector removal and the closure method together. - Confirm closure materials are compatible with the chimney or vent system in use. - Coordinate with existing chimney reuse and liner requirements where the chimney stays in service.
**Do Not** - Leave old vent openings unaddressed on the drawings. - Use "cap by contractor" as a substitute for a reviewable detail. - Assume abandoned openings are harmless to draft or fire separation. - Reuse a chimney without checking for old, unaddressed tie-ins.
Masterbuild QA Lens
On any replacement or renovation scope, ask where the old appliance used to connect - not just where the new one connects. An abandoned opening left unsealed undermines draft on the remaining system and can be a fire-separation gap.
Drawing / Submittal Check
For every appliance removal or replacement on the demolition plan, confirm there's a matching closure detail or note - an appliance schedule that shows removals with no corresponding abandonment note is incomplete.
Common Review Risk
The most common gap is a multi-appliance chimney where one unit is replaced and reconnected, but an old tie-in point from a previous appliance is never traced or closed.
When To Escalate
Escalate any multi-story or common-vent chimney where one appliance is being abandoned while others remain in service, since the closure method can affect draft for the remaining appliances.
Field Tip
On replacement projects, trace every old vent connector before signing off. The drawings should show both the new vent path and the approved closure of whatever opening the old appliance left behind.