IMC 801.10 governs a condition that needs more scrutiny than a typical vent connection: connecting an appliance to a chimney flue that also serves a fireplace. Fireplace flues weren't always designed with a second appliance in mind, and the code treats factory-built and masonry fireplace flues differently.
Plain-English Highlights
Appliance connections to fireplace flues have to comply with 801.10.1-801.10.3. First identify the flue type: factory-built fireplace flue, masonry fireplace flue, or a listed direct connection device. 801.10.1 requires a noncombustible seal below the connection point to keep room air out of the flue, plus permanent access for inspection and cleaning. 801.10.2 requires the appliance to be specifically listed for connection to a factory-built fireplace flue, installed per the manufacturer's instructions.
801.10.3 requires the connector on a masonry fireplace flue to discharge directly into the flue, with the connector and flue both accessible or removable for cleaning.
Permit Proof Chain
Identify fireplace flue type (factory-built or masonry) -> confirm appliance listing covers connection to that flue type -> show the noncombustible seal location and detail -> show connector path discharging directly into the flue -> confirm access for inspection and cleaning of both connector and flue.
Where To Show It
M-001: fireplace flue connection notes and review criteria. M-101: appliance location and chimney connection. M-501: connector, noncombustible seal, access, and cleanout details. M-601: appliance schedule with venting basis. A/LS sheets: fireplace, chimney, rated assembly, and shaft coordination. S sheets: masonry chimney support, if applicable.
**Do** - Identify whether the fireplace flue is factory-built or masonry before detailing the connection. - Confirm appliance listing before connecting to a factory-built fireplace flue. - Show the connector path discharging directly into the masonry flue. - Provide and show access for inspection and cleaning of both the connector and the flue.
**Do Not** - Connect an appliance to a fireplace flue without verifying listing and the applicable code path. - Block access to the connector or flue with the proposed installation. - Allow room air to enter below the connection point - the noncombustible seal is not optional. - Treat factory-built and masonry fireplace flues as interchangeable conditions.
Masterbuild QA Lens
A fireplace-flue connection review has two gates, not one: is the appliance listed for this specific flue type, and can the connector and flue still be inspected and cleaned after installation? Both have to clear before the detail is acceptable.
Drawing / Submittal Check
Verify the appliance manufacturer's listing data explicitly addresses connection to a fireplace flue - general appliance listings often do not cover this condition by default.
Common Review Risk
The recurring miss is a connector detail that satisfies the seal and discharge requirements but blocks future access to the connector or flue once trim, casework, or finishes are installed around it.
When To Escalate
Escalate any appliance connection proposed to an existing masonry fireplace flue without a documented condition assessment, and any factory-built fireplace flue connection where the appliance listing doesn't explicitly name that flue system.
Field Tip
If an appliance is shown connected to a fireplace flue, ask two questions before anything else: is the appliance listed for that specific connection, and can the connector and flue still be inspected and cleaned after the installation is finished?