/ Field knowledge · IMC 801.12–801.13
“Connect to existing chimney” is not an elevation.
The connector enters the chimney at least 12 inches above the lowest interior of the flue. The masonry cleanout sits below the lowest inlet — 6 inches high, upper edge at least 6 inches below that inlet, with a tight-fitting noncombustible cover. “Connect to existing chimney” without those elevations is not a detail.
Educational 2024 International Mechanical Code (IMC) 801.12 and 801.13 from Daily Code Talk. Confirm the adopted edition. Distinct from existing chimney reuse (801.18) and abandoned openings (801.8). This is not a chimney design.
- 801.12: connector entrance not less than 12 inches above the lowest portion of the interior of the chimney flue — so the connector does not discharge into debris, condensate, ash, or soot at the bottom.
- 801.13: masonry chimney flues need a cleanout opening with a minimum height of 6 inches, upper edge at least 6 inches below the lowest chimney inlet opening, and a tight-fitting noncombustible cover.
- Exception: a cleanout is not required for chimney flues serving masonry fireplaces when access is provided through the fireplace opening. Do not assume that exception unless the fireplace opening actually gives that access.
On the set: connector entrance elevation and cleanout size, location, and cover. Access has to survive finishes, equipment, and casework. The vertical relationship is the review: connector inlet above, cleanout below, both accessible.
Hidden behind the new casework
Existing-building reuse is where these sections bite: no entrance elevation, a missing or blocked cleanout, or — most common — a cleanout concealed once construction ends. That is soot, blocked flues, poor draft, and a failed inspection.
Source: Daily Code Talk — IMC 801.12–801.13 · tool: Cleanout screen · reuse: 801.18.3 · existing: 801.18 · solid-fuel: 801.11.
What to send
The chimney section (or photos of the connection and any cleanout), what is being connected, and whether this is masonry fireplace access or a separate cleanout.
If the note is “connect to existing chimney”
Send the photos. Masterbuild will say whether 801.12/801.13 still have no elevations — or 801.18 still has no four-gate evidence.
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. The 12-inch and 6-inch figures are 2024 IMC 801.12–801.13 education from Daily Code Talk — not a chimney design. This page is not legal advice.