/ Field knowledge · IMC 801.18.3
A chimney that passes on size can still fail on the cleanout.
A chimney that passes on size, passageway, and clearance can still fail reuse if the cleanout was never verified. IMC 801.18.3 sends existing masonry back to 801.13: minimum 6-inch opening height, upper edge at least 6 inches below the lowest inlet, tight-fitting noncombustible cover, access maintained. New equipment and finishes on the same project are what usually hide it.
Educational 2024 International Mechanical Code (IMC) 801.18.3 from Daily Code Talk. Confirm the adopted edition. Distinct from new-construction cleanouts (801.12–801.13). This is the reuse check: was the cleanout actually found, measured, and left accessible after the renovation? This is not a cleanout design.
- Show how the chimney will be inspected, cleaned, and maintained — not only the new appliance connection.
- If the cleanout is missing, blocked, undersized, concealed, or inaccessible, the existing chimney condition is not fully reviewable.
- Do not assume a cleanout that was compliant before a renovation remains accessible after new construction concealed it. Treat it as a permanent maintenance access point, not a one-time construction item.
Add a fourth line to the existing-chimney acceptance record for the cleanout alone: location, opening height, elevation below the lowest inlet, cover material, and access condition. Compare M-501 against the equipment layout, casework, and finish plans.
New water heater in front of the old cleanout
Or casework and a finished wall. The reviewer and inspector cannot verify size, elevation, or access until the concealment is corrected. Escalate a missing or undersized cleanout on existing masonry, an unclear elevation vs the lowest inlet, and oil-fired reuse where cleanout has not been coordinated with NFPA 31.
Source: Daily Code Talk — IMC 801.18.3 · 801.13: entrance and cleanouts · size: 801.18.1 · passageway: 801.18.2.
What to send
Photos below the lowest inlet, the new equipment layout, and whether anyone can still open a cleanout after the renovation.
If the new equipment is sitting in front of the cleanout
Send the photo. Masterbuild will say whether 801.18.3 still has no 801.13 evidence — or 801.18.2 still has a sweeping invoice pretending to be continuity.
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 6-inch opening and 6-inch-below-inlet figures are 2024 IMC 801.13 education (via 801.18.3) from Daily Code Talk — not a cleanout design. This page is not legal advice.