The plan-review question is not simply whether a masonry chimney exists. The question is whether the chimney and its liner are compatible with the specific appliance, fuel, flue-gas temperature, condensate exposure, draft condition, and installation instructions.
Plain-English Highlights
IMC 801.15 requires masonry chimneys used to vent fuel-fired appliances to be located, constructed, and sized as specified in the appliance manufacturer's installation instructions. IMC 801.16 requires masonry chimneys to be lined; the lining must be compatible with the connected appliance in accordance with the appliance listing and instructions, and listed lining materials must be installed in accordance with their listing and manufacturer instructions.
For residential-type and low-heat appliances, Section 801.16.1 limits the general lining options to clay flue lining complying with ASTM C315 or equivalent, listed and labeled systems complying with UL 1777, or other approved materials resistant to flue gases and condensate up to 1,800°F (982°C).
Permit Proof Chain
Appliance and fuel identified -> venting category and manufacturer instructions obtained -> chimney location, construction, size, and height documented -> existing condition and flue passage verified when reused -> liner material, standard/listing, size, and compatibility identified -> connector, cleanout, clearances, and termination coordinated -> installation details and inspection access shown -> adopted code and applicable fuel-gas provisions confirmed.
Where To Show It
M-001: appliance, chimney, liner, existing-condition, and code-basis notes. M-101: appliance location, connector route, and chimney connection. M-501: connector, liner, cleanout, support, clearances, penetration, and termination details. M-601: appliance schedule with fuel, vent category, connector size, chimney/liner basis, and manufacturer reference. A/LS sheets: chimney location, shafts, roof, rated assemblies, and combustible clearances. S sheets: support and anchorage where structural work is involved.
**Do** - Match chimney size and construction to the selected appliance instructions. - Identify the liner material, size, standard or listing, and appliance compatibility. - Document the condition, continuity, cleanliness, and draft basis before reusing an existing chimney. - Coordinate connector, cleanout, clearances, termination, and inspection access. - Verify the applicable fuel-gas code path for gas-fired appliances.
**Do Not** - Use "existing chimney to remain" as the complete venting design. - Assume an unlined, deteriorated, oversized, or previously used chimney is acceptable. - Specify a liner without confirming its listing and compatibility with the appliance and flue conditions. - Leave liner selection, resizing, or chimney acceptance to field judgment.
Masterbuild QA Lens
For replacement work, force the design to answer four questions: What is the appliance? What venting condition does it create? What is the existing chimney and liner condition? What evidence proves the proposed combination is allowed? If any answer is missing, the reuse decision is incomplete.
Drawing / Submittal Check
Compare the appliance data, venting instructions, chimney survey, and liner submittal. The drawings should identify chimney dimensions and construction, liner material and listing, connector size and material, cleanout and access, termination, clearances, and any required resizing or relining. A generic note cannot replace this comparison.
Common Review Risk
A high-efficiency replacement appliance is connected to an old masonry chimney based only on an existing-condition note. No liner type or condition is documented, the flue is oversized for the new duty, condensate exposure is ignored, and the connector or termination is not coordinated. The likely outcomes are poor draft, condensation, corrosion, flue-gas leakage, carbon-monoxide risk, and failed inspection.
When To Escalate
Escalate existing chimney reuse, fuel conversion, appliance-category changes, multiple-appliance venting, visible liner deterioration, missing chimney dimensions, uncertain draft or condensation performance, reduced clearances, and any proposed liner outside the general Section 801.16.1 options. Section 801.18 adds condition, resizing, cleanout, and clearance checks when appliances are connected to existing chimneys or vents. For gas-fired appliances, follow the applicable fuel-gas code and the appliance listing rather than relying on IMC Chapter 8 alone.
Field Tip
On replacement projects, put the appliance data and chimney survey side by side. If the plans do not identify liner type, listing, size, condition, compatibility, and the manufacturer-based venting basis, the chimney design is not complete enough for permit or construction.