/ Field knowledge · IMC 801.10
A fireplace flue is not a spare vent connection.
Connecting an appliance to a chimney flue that also serves a fireplace is not a typical vent connection. Factory-built and masonry fireplace flues are different code paths. Two gates: the appliance has to be listed for that flue type, and the connector and flue still have to be inspectable and cleanable after trim is in.
Educational 2024 International Mechanical Code (IMC) 801.10 from Daily Code Talk. Confirm the adopted edition. Distinct from solid-fuel dedicated flues (801.11) and entrance and cleanouts (801.12–801.13). This is not a fireplace design.
- Identify the flue type first: factory-built fireplace flue, masonry fireplace flue, or a listed direct-connection device. They are not interchangeable.
- 801.10.1: a noncombustible seal below the connection point so room air stays out of the flue, plus permanent access for inspection and cleaning. The seal is not optional.
- 801.10.2: the appliance must be specifically listed for connection to a factory-built fireplace flue, installed per the manufacturer. General appliance listings often do not cover this by default.
- 801.10.3: on a masonry fireplace flue, the connector discharges directly into the flue, and both the connector and the flue are accessible or removable for cleaning.
On the set: flue type, appliance listing for that connection, seal location, connector path discharging into the flue, and access that survives casework and finishes.
The seal is on the detail. The access is not.
The recurring miss is a connector that satisfies the seal and discharge but blocks future access once trim, casework, or a gas-log set is installed. Escalate existing masonry fireplace flues without a documented condition assessment, and factory-built flues where the listing does not name that flue system.
Source: Daily Code Talk — IMC 801.10 · tool: Fireplace-flue screen · solid-fuel: 801.11 · cleanouts: 801.12–801.13.
What to send
Fireplace type (factory-built vs masonry), the appliance cut sheet, and photos of the flue and how you would still clean it after the connection.
If a water heater or insert is tying into a fireplace flue
Send the cut sheet and the flue type. Masterbuild will say whether 801.10 even has a listed path — or access dies behind the new surround.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. This page is 2024 IMC 801.10 education from Daily Code Talk — not a fireplace or connector design. This page is not legal advice.