13.3 Vent Terminations & Clearances to Openings
Key Takeaways
- 2024 IFGC 503.6.6 and IMC 802.6 require a Type B or L gas vent to terminate not less than 5 feet above the highest connected draft hood or flue collar; a Type B-W vent is 12 feet above the bottom of the wall furnace.
- Gas vents 12 inches or less in size and at least 8 feet from a vertical wall follow Figure 503.6.5’s roof-slope table (1.0 foot above a flat-to-6/12 roof, climbing with slope); vents over 12 inches or closer than 8 feet to a wall terminate 2 feet above the roof penetration and 2 feet above any building within 10 feet (503.6.5).
- 2024 IFGC 503.5.4 requires a residential-type or low-heat masonry or factory-built chimney to extend 3 feet above the highest roof penetration and 2 feet higher than any portion of a building within 10 feet, and not less than 5 feet above the highest connected draft hood or flue collar.
- 2024 IFGC Table 503.8 Row B places a nondirect-vent through-wall terminal 4 feet below or horizontally from, or 1 foot above, an openable door or window; direct-vent uses the 6/9/12-inch input scale up to 150,000 Btu/h.
- Mechanical-draft terminations adjacent to walkways shall be not less than 7 feet above the walkway (IMC 804.3.4 / 804.3.5 and Table 503.8 Row J); IMC 804.3.3 keeps a power-exhauster outlet at least 10 feet from a lot line or adjacent building.
A legal connector into a legal vent still fails the inspection if the cap is in the wrong place. Terminations keep combustion products out of windows, intakes, walkways, and snowdrifts. 2024 IFGC 503.6.5 through 503.8 and IMC 802 and 804 are the two maps. Gas vents use the IFGC. Oil, pellet, integral-vent, and mechanical-draft systems for other fuels use the IMC. Direct-vent terminals follow the manufacturer and, for gas, Table 503.8.
Roof terminations — 5-foot height, slope table, 3/2/10
Minimum vent height — 503.6.6 / IMC 802.6. A Type B or L gas vent shall terminate not less than 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. IMC 802.6 is the same 5-foot rule above the highest connected flue collar, with exceptions for direct-vent, outdoor integral-vent, and pellet vents (manufacturer). A Type B-W vent is a different number: 12 feet above the bottom of the wall furnace (503.6.6). Single-wall metal pipe also needs the 5-foot height and the 2-foot / 10-foot roof pair (503.7.3).
Gas-vent roof location — 503.6.5 (confirmed 2024). Pick one of the listed paths:
- Gas vents 12 inches or less in size and located not less than 8 feet from a vertical wall or similar obstruction terminate above the roof per Figure 503.6.5 (the roof-slope table).
- Gas vents over 12 inches in size, or located less than 8 feet from a vertical wall or similar obstruction, terminate not less than 2 feet above the highest point where they pass through the roof and not less than 2 feet above any portion of a building within 10 feet horizontally.
- The industrial, direct-vent, integral-vent, mechanical-draft, and hood exceptions in 503.2.2, 503.2.3, 503.2.4, 503.3.3, and 503.3.4.
Figure 503.6.5 minimum height H above the roof for those small, away-from-wall vents:
- Flat to 6/12 → 1.0 ft
- Over 6/12 to 7/12 → 1.25 ft
- Over 7/12 to 8/12 → 1.5 ft
- Over 8/12 to 9/12 → 2.0 ft
- Then 2.5, 3.25, 4.0, 5.0, 6.0, 7.0, 7.5, and 8.0 ft at over 20/12 to 21/12.
A 4-inch Type B 10 feet from a parapet on a 4/12 roof may stop 1.0 foot above the roof if the 5-foot draft-hood height is also met. Move that same 4-inch vent to 6 feet from the wall and you leave the figure: you now need 2 feet above the roof and 2 feet above that wall if the wall is within 10 feet. A 14-inch gas vent never gets the 1.0-foot row.
IMC 802.5 is simpler for Type L: not less than 2 feet above the highest point of the roof penetration and not less than 2 feet higher than any portion of a building within 10 feet. There is no 12-inch / 8-foot slope-table shortcut in 802.5.
Chimneys — 503.5.4. Residential-type or low-heat chimneys extend not less than 3 feet above the highest point where they pass through the roof and not less than 2 feet higher than any portion of a building within 10 feet. They also extend not less than 5 feet above the highest connected draft hood or flue collar. Medium-heat chimneys: 10 feet higher than any building within 25 feet. That 3/2/10 pair is not the Type B figure. A masonry chimney that stops 1.0 foot above a 4/12 roof because someone applied Figure 503.6.5 is a 503.5.4 fail.
Caps, shrouds, forced-air inlets, walls. 503.6.7: the gas vent extends through the flashing, roof jack, or thimble and terminates with a listed cap or listed roof assembly. IMC 802.4 requires a listed Type L cap. 503.6.5.1 / 503.5.4: decorative shrouds only if listed for that specific vent or chimney system. A shop-made “hat” is not a listed cap. Spark arrestors belong on solid-fuel chimneys where the IBC or the listing requires them; they are not a substitute listed Type B cap. 503.6.8: a gas vent terminates not less than 3 feet above any forced-air inlet located within 10 feet. 503.6.9: a gas vent through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets except as 503.2.3 (direct-vent) or 503.3.3 (mechanical draft) allow. 502.7.1 / IMC 802.9: a door shall not swing within 12 inches horizontally of a vent terminal; doorstops or closers shall not be used to buy that clearance.
Sidewall terminations — Table 503.8 and mechanical draft
503.8 / Figure 503.8. Through-the-wall direct-vent and nondirect-vent terminals follow Table 503.8. Exception: the table does not apply to the combustion-air intake of a direct-vent appliance. 503.2.3 still sends listed direct-vent appliances to the manufacturer and to 503.8 for the through-wall terminal. 503.16 permanently seals the annular space around any exterior-wall vent penetration so flue gas cannot re-enter the wall cavity.
| Table 503.8 row (2024 IFGC) | Direct-vent terminal | Nondirect-vent terminal |
|---|---|---|
| A — above finished grade, veranda, porch, deck, or balcony | 12 inches (keep condensing kits above ice and snow accumulation) | 12 inches |
| B — openable window or door | 6 in. if ≤10,000 Btu/h; 9 in. if >10,000 and ≤50,000; 12 in. if >50,000 and ≤150,000; above 150,000 Btu/h follow the manufacturer and not less than the nondirect-vent Row B distances | 4 feet below or to the side of the opening, or 1 foot above the opening |
| C — nonopenable window | None unless the manufacturer specifies | None unless the manufacturer specifies |
| D, E, F, G — ventilated soffit within 2 feet of centerline; unventilated soffit; outside corner; inside corner | None unless the manufacturer specifies | None unless the manufacturer specifies |
| H — nonmechanical (gravity) air-supply inlet, and combustion-air inlet to any other appliance | Same as Row B | Same as Row B (4 ft below/side or 1 ft above) |
| I — mechanical air-supply inlet | 10 feet horizontally from the inlet or 3 feet above the inlet | Same 10 ft / 3 ft pair |
| J — paved sidewalk or driveway on public property | 7 feet, and shall not be located above public walkways or other areas where condensate or vapor can cause a nuisance or hazard | Same 7-foot / no-nuisance rule |
| K — underside of veranda, porch, deck, or balcony | 12 inches if the space below is open on not less than two sides; prohibited if only one side is open | Same |
Row B is the exam row. A nondirect-vent power-vent water heater through the wall beside an operable window must be 4 feet beside it or below it, or 1 foot above the head of the window. “Nine inches because it is under 50,000 Btu/h” is the direct-vent scale, not the atmospheric or mechanical-draft nondirect scale. Row H uses the same numbers for a gravity combustion-air or makeup-air opening. Row I is the mechanical-intake pair you already saw in 503.6.8’s spirit: 10 feet away or 3 feet above.
IMC 804 mechanical draft (non-gas). Mechanical draft systems are listed to UL 378 (804.3). Forced-draft and the positive-pressure portions of induced-draft systems are gas-tight (804.3.1). The burner shall not run unless the exhauster runs (804.3.2). 804.3.3: a power-exhauster termination is not less than 10 feet from a lot line or from adjacent buildings, and the exhaust is directed away from the building. 804.3.4 horizontal and 804.3.5 vertical both require: 7 feet above a walkway; 3 feet above a forced-air inlet within 10 feet; 4 feet below, 4 feet horizontally from, or 1 foot above any door, window, or gravity air inlet; plus the IMC extras (3 feet from an interior corner, 3 feet from an oil-tank vent or gas meter, 12 inches above finished grade, a rain cap on vertical terminations, and 3 feet horizontally from a roof structure on vertical terminals). 804.3.6: a natural-draft appliance shall not connect on the discharge side of a mechanical flue exhauster.
Condensing sidewall kits, ice, and snow. Category IV and other condensing appliances use the listed termination kit in the appliance manual (503.4.1, 503.2.3, 503.9). Table 503.8 Row A’s 12 inches above grade is the code floor, not a snow-country ceiling — the manufacturer will push the kit above expected snow and ice so the outlet and intake cannot glaze shut. 503.9 requires condensate collection and disposal for Category II and IV and noncategorized condensing appliances. Do not terminate a condensing sidewall kit over a public walkway (Row J) or where the plume becomes a slip-and-fall. IMC 804.1 still hands direct-vent terminals for non-gas appliances to the manufacturer; 804.2.1 gives integral-vent natural-draft terminals 9 inches to openings and forced-draft integral-vent terminals 12 inches to openings.
A 4-inch Type B gas vent serving a draft-hood furnace is 10 feet from the nearest vertical wall on a 4/12 roof. The vent already has more than 5 feet of height above the draft hood. What 2024 IFGC 503.6.5 termination applies?
A nondirect-vent through-wall terminal is proposed 2 feet to the side of an operable window. What does 2024 IFGC Table 503.8 Row B require?
A mechanical-draft vent terminates horizontally next to a public sidewalk. What minimum height above the walkway do 2024 IMC 804.3.4 and IFGC Table 503.8 Row J require?