Combustion Air

Ducts min. cross-section dimension 3in. . . . . .[2407.10,11] {704.1.2}
No dampers in combustion air ducts . . . . .[1701.3,2407.15] {704.2}
Return >10ft. min.from combustion . . . ..F-m5 [1602.3X2,2440.5-4X] {404.1X}
Joist/stud space duct OK if max. 1 fire stop removed . . . . . . . . . . .[2407.15X] {704.1.1X}
Screened (except in attic) with 4in. mesh . . . . . . . .[1703.6] {702.3}
Screens prohibited in duct to attic . . . . . .[1703.4, 2407.15] {704.3}
Area of louvres-metal x 75%, wood x 25% . . . . . . . . . . .[1701.5, 2407.14] {702.3,local}

Unconfined space drawing from indoors:
Unconfined space is >50cu.ft./1000Btu/hr. . . . .[202,2403] {223.0}
Infiltration suff. source to unconfined space . . . F-m6[1702.1,2407.10] {701.3}

Confined space drawing from indoors:
Min. 100sq.in.
openings or 1sq.in./1000Btus . . . . .F-m7 [1702.2,2407.10] {703.4. & t7-A}
Openings in upper and lower 12in. . .F-m7 [1702.2,2407.10] {702.1}

Tight construction:
Confined space is <50cu.ft./1000Btu/hr. . . . . . .[202,2403] {205.0}
1 upper opening only OK if air from outside . . . .[2407.11.2] {702.1X3}

From Underfloor:
Only lower opening connected to underfloor area . .[1703.2,2407.11.1] {703.2}
Foundation vents supplying underfloor area min. 2x required combustion air openings (min. 200sq.in.) .............................................................. .[1703.5] {703.2.1}
Crawlspace must meet min. building code standard clearance (18in. between earth and joists) ..........................................................................[323.1] {703.2.2}
Min. 1sq.in./4,000Btu/hr. each . . .F-m9 [1703.2.1,2407.11] {t7-A}

From Attic:
Attic height must be min. 30in. . . . . . . . . . . . . . . . . . .[n/a] {703.1.2.1}
Min. vent area 1sq.in./4,000Btu/hr. each . . . . . . .F-m8 [1703.2.1,2407.11] {T7-A}
Opening sleeved to 6in. above joist/26ga. sheet
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [1703.4.2,2407.15] {703.1.2.3}
No screens . . . . . . . . . . . . . . . . . . . . .[1703.4.4,2407.15] {704.3}
Maintain duct separation to source . . . . . .[1703.2,2407.15] {704.1.6}

Flue

General (Gravity Gas Category 1) IRC UMC
Install per manu. instructions and listing . . . . . . .[2426.6.1] {803.1}
Induced-draft can be "gravity vent” . . . . . . . . . .[2426.6.8.1] {manu}
Min. 5ft. height from collar (except wall furnace) . .[2426.6.6] {806.2}
Min. termination 12ft. from base of wall furnace . .[2426.6.6] {806.3}
Bends 45° max. except one of 60° . . . . . . . . . . .[2426.6.4] {805.1}

Connector
Size--Min. 7sq.in. or 3in. diameter . . . . . . . . . .[T2427.2(1)] {808.2}
Size--Max. 7x diameter of vent collar or draft hood [2427.2.8] {n/a}
No solid fuel and gas in same vent . . . . . . . . . .[2426.5.6.1] {802.4}
Flue supported from ground needs 2in. conc. pad . . .[manu.] {804.2}
Sheet metal shield [to 2in.] above insulation in attic (BW only)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [2425.4] {807.5}
No single-wall in attic or cold or concealed space [2426.7.6] {815.1.7}
Uninsulated connector <=75% of vert. vent . . . . . .[2426.10.9] {815.11}
Insulated connector (type B) <=100% of vert. vent [2426.10.9] {815.11}
Slope min. 4in./ft. toward appliance . . . . . . . . .[2426.10.8] {805.2}
Sheet metal screws to appliance vent collar . . . .[2426.10.7] {815.1.9}
{3} Sheet metal screws at connection to vent. . .[2426.10.12] {815.1.9}
Min. clear to combustible for single wall is 6in. . .[T2426.7.7] {T3-C}

Appliances with Common Venting
Multiple connectors join as high as possible in room . ..[2426.10.3.4] {809}
All connectors must enter on same floor . . . . . . . . . . .[n/a] {809}
Connectors staggered where they enter . . . . . . . . . . . .[n/a] {809.2}
Flue must equal largest connector +50% of others . . .[2426.10.3.4] {809.3}

Forced Vent (Category IV) & Integral Vents
Flue must be gas tight . . . . . . . . . . . . .[2424.10, 2426.3.3] {817.2}
No natural and forced-vent to common flue . . . . . .[2426.3.3] {817.3}

Termination Clearances:
"B" Vents:
2ft. above vert. surface within 8ft. . . . . . . . . . . .[2426.6.5] {806.4}
Min. 1ft. above low-slope (<=6:12) roof. . . . . .T-m1 [2426.6.5] {T8-A}

"L" vents:
"L" vents (oil) min. 2ft. above anything within 10ft. .[1804.2.4] {806.5}

Forced Vents & Integral Vents IRC UBC
Min. 3ft. above forced-air inlet within 10ft. . . . . . . .[2426.8] {806.6,7}
4ft. below or side and 1ft. above window or door . . .[2426.8] {806.6,7}
Min. 1ft. from [above] any building opening . . . . . . .[2426.8] {816.6,7}
Size per manu. instructions . . . . . . . . . . . . . . .[2426.6.8.2] {802.5}
Slope horiz. plastic vent 2in./ft. to appliance . . . . .[2426.9] {802.5}
Supports for horiz. plastic max. 4ft. apart . . . . . . .[T2605.1] {UPCT3-2}
Supports should allow thermal expansion/contraction . .[2426.6.9] {802.5}

Direct Vent Wall Heater Flue Termination:
0-10K Btu/hr. min. 6in. clearance to bldg. openings [2426.8] {Ø}
0-50K Btu/hr. min. 12in. {9in.} . . . . . . . . . . . . . . .[2426.8] {806.6X}
12in. clearance to ground
{and 4ft. to prop. line} . . . . . . . . . . . . . . . . . . . .T-m2 [2426.8] {806.6X}

Gas Vent Entering Masonry Chimney
Enter min. 12in. {6in.} from bottom . . . . . . . . . . . .[2424.9] {813.2.6}
Must be lined {if >1 side on exterior} with clay or metal . [2426.5.2] {813.2}
Cross-sectional area not >7x {4x} size of gas vent [2427.2.8] {813.2.2}