VENTING TABLES CATEGORY I CENTRAL FURNACES COPYRIGHT 1990 GAS APPLIANCE MANUFACTURERS ASSOCIATION GAMA Venting Tables 7507-183 REVISED: JULY, 1991 Form: IM-GA1A-09 Cancels: IM-GA1A-06 Printed in U.S.A. 1-95 Catalog No. 92-33GA-1A15 This document was created with FrameMaker 4.0.4
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When using Venting Tables Category I Central Furnaces supplement furnished with this Installation Instructionpackage, use the Terms table below to explain American and Canadian terminology which differs.
TERMS
Section III. General Venting Requirements:
Item 8 of this section applies only to United States instructions. Figures 1 and 2 should not be used as a referencefor vent termination in Canada. Use the procedures established by local authorities or in the absence of localauthorities, those set by the CAN/CGA–B149 Installation Codes.
AMERICAN TERM CANADIAN TERM AND DEFINITION
Category I Central Furnaces In Canada, this type of furnace is a conventionally vented (vertical natural draft) furnace with or without a drafthood.
National Fuel Gas Code-NFPA 54/ANSI Z223. 1-1992
National Standard of Canada, CAN/CGA–B149.1 and .2–M91 Natural Gas and Propane Installation Codes with Amendment No. 1
GAMA VENTING TABLESFOR
CATEGORY I CENTRAL FURNACES
This booklet contains new venting tables designed specifically for use with Category I central furnaces.These tables are unique, in that, industry wide venting tables now exist for fan-assisted combustion system centralfurnaces. Venting tables for these types of appliances are not contained in the National Fuel Gas Code (NFPA 54/ANSI Z223.1-1988).
All requirements contained in this booklet apply to both Category I drafthood equipped central furnaces aswell as fan-assisted combustion system central furnaces. At no time should a venting system for a listed CategoryII, III, or IV central furnace be sized with these tables. The National Fuel Gas Code (NFPA 54/ANSI Z223.1-1988)may also be used to size venting systems for drafthood equipped central furnaces. However, at this time, theNational Fuel Gas Code does not include alternate sizing methods for fan-assisted combustion systems. There-fore, until engineering data is developed to allow alternate sizing methods for Category I fan-assisted central fur-naces, the enclosed venting tables must be used for fan-assisted combustion system central furnaces. Thesetables apply to venting single appliances and common venting multiple appliances in both metal and masonrychimneys.
The new venting tables were developed by Battelle under contract (GRI-5088-245-1728) to the GasResearch Institute (GRI). The computer program (VENT-II) developed by Battelle Columbus generated the vent-ing tables in this booklet and this procedure has been accepted by the American Gas Association Laboratories asan appropriate engineering methodology for determining venting requirements of Category I central furnaces.
For your information, the general venting requirements listed in this booklet are not intended to be used ascomplete installation instructions and represent only a partial list of venting considerations.
For venting applications that fall outside the parameters of the new venting tables, refer to the furnacemanufacturer’s complete installation instructions, the specific vent manufacturer’s complete installation instruc-tions, and state and local codes.
GRI DISCLAIMER
LEGAL NOTICE:
This information is, in part, a result of work performed by Battelle under the sponsorship ofthe Gas Research Institute (GRI). Neither GRI, members of GRI, nor any person acting on behalf of either:
a. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, orusefulness of this information, or that the use of any apparatus, method, or process disclosed may notinfringe privately owned rights; or
b. Assumes any liability with respect to the use of, or for damages resulting from the use of, any information,apparatus, method, or process disclosed.
1
I. INTRODUCTION
This booklet contains the current definitions, instruc-tions, and tables necessary to vent todays modernCategory I Gas Fired Appliance. A variety of defini-tions of new terms describing today’s gas appliancesare included to supplement the actual venting tableswhich have been generated to correctly vent variouscombinations of Category I Appliances using Type Bor single-wall metal vent connectors attached toType B vents or masonry chimneys. Tables are alsoincluded covering similar venting material combina-tions when applied to common venting arrangementsof two or more appliances.
Finally, a series of examples are presented demon-strating how the vent tables are used to size the ventconnector and the vertical vent for a variety of typicalapplications.
II. DEFINITION OF TERMS
“Fan Assisted Combustion System”
An appliance equipped with anintegral mechanical means toeither draw or force products ofcombustion through the com-bustion chamber and/or heatexchanger.
“FAN Min” refers to the minimum applianceinput rating of a Category I appli-ance with a fan-assisted com-bustion system that could beattached to the vent.
“FAN Max” refers to the maximum applianceinput rating of a Category I appli-ance with a fan-assisted com-bustion system that could beattached to the vent.
“NAT Max” refers to the maximum applianceinput rating of a Category I appli-ance equipped with a drafthoodthat could be attached to the vent.There are no minimum applianceinput ratings for drafthood-equipped appliances.
“FAN+FAN” refers to the maximum combinedinput rating of two or more fan-assisted appliances attached tothe common vent.
“FAN+NAT” refers to the maximum combinedinput rating of one or more fan-assisted appliance and one ormore drafthood-equipped appli-ance attached to the commonvent.
“NAT+NAT” refers to the maximum combinedinput rating of two or moredrafthood-equipped appliancesattached to the common vent.
“NR” means not recommended due topotential for condensate forma-tion and/or pressurization of theventing system.
“NA” means not applicable due tophysical or geometric constraints.
DraftHood A device built into an appliance,or made a part of the vent con-nector from an appliance, whichis designed to (1) provide for theready escape of the flue gasesfrom the appliance in the event ofno draft, backdraft, or stoppagebeyond the drafthood, (2) preventa backdraft from entering theappliance, and (3) neutralize theeffect of stack action of the chim-ney or gas vent upon the opera-tion of the appliance.
Vent A passageway used to conveyflue gases from gas utilizationequipment, or their vent connec-tors, to the outside atmosphere.
Vent Connector The pipe or duct which connectsa fuel-gas burning appliance to avent or chimney.
Flue Collar That portion of an appliancedesigned for the attachment ofa drafthood, vent connector, orventing system.
Categorized Vent Diameter
The minimum vent diameter per-missible for Category I appli-ances to maintain a nonpositivevent static pressure when testedin accordance with nationally rec-ognized standards.
VENTING REQUIREMENTS FOR CATEGORY I APPLIANCES
2
III. GENERAL VENTING REQUIREMENTS
All requirements contained in this document apply toboth Category I draft hood equipped and fan-assisted combustion appliances. At no time should aventing system for a listed Category II, III, or IV appli-ance be sized with these Tables. The alternate sizingmethods described in the National Fuel Gas Code(NFPA54/ANSI Z223.1-1988) may also be used tosize the venting system for a drafthood equippedappliance. At this time, alternate sizing methodshave not been developed for fan-assisted appli-ances. Therefore, until engineering data is devel-oped to allow alternate sizing methods for Category Ifan-assisted appliances, the vent tables must beused.
1) The venting tables included in this instructionapply to vents and chimneys internal to thestructure below the roof line. Exterior chimneysor vents not enclosed by the structure or achase below the roof line may experience con-tinuous condensation depending on locality.Consult local gas utility, appliance manufac-turer and/or local codes. A chimney with one ormore sides exposed to the outside of the struc-ture is considered to be an exterior chimney. AType B or listed chimney lining system passingthrough an unused masonry chimney flue is notconsidered to be exposed to the outdoors.
2) If the vent or connector size determined fromthe tables is smaller than the appliance draft-hood outlet or flue collar, the smaller size maybe used provided:
a) The total vent height “H” is at least 10 FT.
b) Vents or connectors for appliance draft-hood outlets or flue collars 12 inches indiameter or smaller are not reduced morethan one table size (e.g. 12 inches to 10inches is a one size reduction).
c) Vents or connectors for appliance draft-hood or flue collars above 12 inches indiameter are not reduced more than twotable sizes (e.g. 24 inches to 20 inches is atwo size reduction).
d) The maximum capacity listed in the tablesfor a fan-assisted appliance is reduced by10% (0.90 x maximum capacity).
e) The drafthood outlet is greater than 4inches in diameter. Do not connect a 3inch diameter vent or connector to a 4 inchdiameter drafthood outlet. This provisiondoes not apply to fan-assisted appliances.
3) Single appliance venting configurations withzero lateral lengths, Tables 1 & 2, are assumedto have no elbows in the vent system. For allother vent configurations, the vent system isassumed to have two 90
°
elbows. For eachadditional 90
°
elbow, or equivalent* beyondtwo, the maximum capacity listed in the ventingtable should be reduced by 10 percent (0.90 xmaximum listed capacity).
* Two 45
°
elbows are equivalent to one 90
°
elbow.
4) The common venting Tables 3, 4, 7, & 8 weregenerated using a maximum horizontal ventconnector length of 1 1/2 feet (18 inches) foreach inch of connector diameter as follows:
The vent connector should be routed to thevent utilizing the shortest possible route. Con-nectors with longer horizontal lengths thanthose listed above are possible under the fol-lowing conditions:
a) The maximum capacity (Fan Max. or NatMax.) of the vent connector shall bereduced 10% for each additional multipleof the length listed above. For example,the maximum length listed above for a 4inch connector is 6 feet. With a connectorlength greater than 6 feet but not exceed-ing 12 feet, the maximum capacity mustbe reduced by 10% (0.90 x maximum ventconnector capacity). With a connectorlength greater than 12 feet but not exceed-ing 18 feet, the maximum capacity mustbe reduced by 20% (0.80 x maximum ventcapacity).
CONNECTOR DIAMETER
(INCHES)
MAXIMUM HORIZONTALCONNECTOR LENGTH
(FEET)3 4 1/2 4 65 7 1/26 97 10 1/28 129 13 1/2
10 1512 1814 2116 2418 2720 3022 3324 36
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b) The minimum capacity (Fan Min.) shall bedetermined by referring to the correspond-ing single appliance table (Tables 1 and 2).In this case, for each appliance the entirevent connector and common vent from theappliance to the vent termination would betreated as a single appliance vent, as if theother appliances were not present.
5) If vent connectors are combined prior to enter-ing the common vent, the maximum commonvent capacity listed in the common ventingtables must be reduced by 10%, the equivalentof 1 (one) 90
°
elbow (0.90 x maximum commonvent capacity). See Figure 7. The horizontallength of the common vent connector manifold(L) should not exceed 1-1/2 feet (18 inches) foreach inch of common vent connector manifolddiameter.
6) If the common vertical vent is offset as shownin Figure 8, the maximum common vent capac-ity listed in the common venting tables shouldbe reduced by 20%, the equivalent of 2 (two)90
°
elbows (0.80 x maximum common ventcapacity). The horizontal length of the offsetshall not exceed 1 1/2 feet for each inch ofcommon vent diameter.
7) The common vent diameter must always be atleast as large as the largest vent connectordiameter. All interconnection fittings must alsobe the same size as the common vent.
8) Type B gas vents shall terminate above theroof surface with a listed cap or a listed roofassembly in accordance with the terms of theirrespective listings and the vent manufacturer’sinstructions.
VENT CAPS 12˝ AND SMALLERListed gas venting systems using listed ventcaps 12˝ and smaller in size may terminate inaccordance with the VENT TERMINATIONTABLE. (SEE FIGURE 1)
VENT CAPS LARGER THAN 12˝Listed vent caps larger than 12˝ must belocated at least 2 feet above the highest pointand at least 2 feet higher than any portion of abuilding within a horizontal distance of 10 Feet.(SEE FIGURE 2)
9) Use sea level input rating when determiningmaximum capacity for high altitude installation.Use actual input rating for determining mini-mum capacity for high altitude installation.
GAS VENT TERMINATION TABLE
*THIS REQUIREMENT COVERS MOST INSTALLATIONS
ROOF PITCH MINIMUM HEIGHT
FLAT TO 7/12 1.0 FEET*OVER 7/12 TO 8/12 1.5 FEETOVER 8/12 TO 9/12 2.0 FEETOVER 9/12 TO 10/12 2.5 FEETOVER 10/12 TO 11/12 3.25 FEETOVER 11/12 TO 12/12 4.0 FEETOVER 12/12 TO 14/12 5.0 FEETOVER 14/12 TO 16/12 6.0 FEETOVER 16/12 TO 18/12 7.0 FEETOVER 18/12 TO 20/12 7.5 FEETOVER 20/12 TO 21/12 8.0 FEET
VERTICAL WALL
LISTED CAP
MINIMUM HEIGHT
8′ MIN.
LOWEST DISCHARGE OPENING
THE VENT TERMINATION SHOULD NOT BE LESS THAN 8 FT. FROM A VERTICAL WALL
FIGURE 1 – VENT CAPS 12″ OR SMALLER
12
X
ROOF PITCH IS X/12
2′ MIN.
10′ MIN.
FIGURE 2 – VENT CAPS LARGER THAN 12″
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10) No portion of the venting system can extendinto, or pass through any circulating air duct orplenum.
11) All vent pipe passing through floors, walls, andceilings must be installed with the listed clear-ance to combustible materials and be firestopped according to local codes. In theabsence of local codes, refer to NFGC (Z223.1)
12) Vent connectors serving Category I appliancesshall not be connected to any portion ofmechanical draft systems operating under pos-itive pressure such as Category III or IV Vent-ing Systems.
13) A Category I appliance must never be con-nected to a chimney that is servicing a solidfuel appliance. If a fireplace chimney flue isused to vent this appliance, the fireplace open-ing must be permanently sealed.
14) A vent connector shall be supported withoutany dips or sags and shall slope a minimum of1/4 inch per lineal foot of connector, backtowards the appliance.
15) Vent connectors shall be firmly attached todrafthood outlets or flue collars by sheet-metalscrews or other approved means, except ventconnectors of listed Type B vent material whichshall be assembled in accordance with themanufacturer’s instructions. Joints betweensections of single wall connector piping shall befastened by sheet-metal screws or otherapproved means.
16) When the vent connector used for Category Iappliances must be located in or pass througha crawl space or other area which may be cold,that portion of the vent connector shall be oflisted double-wall Type B vent material or mate-rial having equivalent insulation qualities.
17) The entire length of single wall metal vent con-nector shall be readily accessible for inspec-tion, cleaning, and replacement.
18) For appliances with more than one input rate,the minimum vent or connector (Fan Min) capac-ity determined from the tables shall be less thanthe lowest appliance input rating and the maxi-mum vent or connector (Fan or Nat Max.) capac-ity determined from the tables shall be greaterthan the highest appliance input rating.
19) For single appliance vents:
a) If the vertical vent or tile lined chimney hasa larger diameter or flow area than thevent connector, use the vertical vent diam-eter to determine the minimum ventcapacity and the vent connector diameterto determine the maximum vent capacity.The flow area of the vertical vent, however,shall not exceed 7 times the flow area ofthe listed appliance categorized vent area,drafthood outlet area or flue collar areaunless designed in accordance withapproved engineering methods. See Table9 for calculated areas.
b) For multiple appliance vents:
The flow area of the largest section of ver-tical vent or chimney shall not exceed 7times the smallest listed appliance catego-rized vent area, flue collar area, or drafthood outlet area unless designed in accor-dance with approved engineering meth-ods. See Table for calculated areas.
c) In no case, shall the vent connector beupsized more than 2 consecutive tablesize diameters over the size of the draft-hood outlet, flue collar outlet, or listedappliance categorized vent. Example: Anappliance with a 4 inch diameter flue outletcollar or drafthood outlet cannot be ventedwith a connector diameter larger than 6inches.
20) Masonry chimneys used to vent Category Icentral furnaces must be either tile-lined orlined with a listed metal lining system or dedi-cated gas vent. Unlined masonry chimneys areprohibited. (See Note 1).
21) A fan assisted furnace may be common ventedinto an existing masonry chimney provided:
a. The chimney is currently serving at leastone drafthood equipped appliance.
b. The vent connectors and chimney aresized in accordance with Tables 7 & 8.
SINGLE APPLIANCE VENTING OF A FANASSISTED FURNACE INTO A TILE LINED,MASONRY CHIMNEY IS PROHIBITED. THECHIMNEY MUST FIRST BE LINED WITHEITHER TYPE B VENT SIZED IN ACCOR-DANCE WITH TABLES 1 OR 2 OR A LISTEDSINGLE WALL, METAL LINING SYSTEM,SIZED IN ACCORDANCE WITH NOTE 22.
TT D
∗( )
2
4-------------------------
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22) Listed, corrugated metallic chimney liner sys-tems in masonry chimneys shall be sized byusing Tables 1 or 2 for dedicated venting andTables 3 or 4 for common venting with the max-imum capacity reduced by 20% (0.80 x maxi-mum capacity) and the minimum capacity asshown in the applicable table. Corrugatedmetal vent systems installed with bends or off-sets require additional reduction of the ventmaximum capacity (See Note 6).
23) For multiple units of gas utilization equipmentall located on one floor, available total height“H” is measured from the highest drafthoodoutlet or flue collar up to the level of the cap orterminal. Connector rise “R” is measured fromthe drafthood outlet or flue collar to the levelwhere the vent gas streams come together.(Not applicable to multi-story).
24) For multi-story installations, available totalheight for each segment of the system “H” isthe vertical distance between the highest draft-hood outlet or flue collar entering that segmentand the centerline of the next higher intercon-nection tee (See Figure 13).
25) The size of the lowest connector and of thevertical vent leading to the lowest interconnec-tion of a multi-story system must be in accor-dance with Table 1 OR 2, for available totalheight “H” up to the lowest interconnection(See Figure 14).
26) Common vents in multi-story systems shall betype B when used in multi-story systems andhave no offsets.
27) Numbers followed by an asterisk (*) in Table 6,indicate the possibility of continuous condensa-tion, depending on locality. Consult appliancemanufacturer, local serving gas supplier, and/orauthority having jurisdiction.
28) In a single run of vent or vent connector, morethan one diameter and type of pipe are permit-ted to be used, provided that all the sizes arepermitted by the tables.
29) If the desired vent height and connector riseand/or lateral are between the table entries, lin-ear interpolation is permitted for calculation ofthe permissible appliance input ratings. Extrap-olation beyond the table entries is not recom-mended. (See Example 7)
30) All combinations of pipe sizes, single-wall, anddouble-wall metal pipe are allowed within anyconnector run(s) or within the common ventprovided ALL of the appropriate tables permitALL of the desired sizes and types of pipe, as ifthey were used for the entire length of the sub-ject connector or vent. If single-wall and Type Bdouble-wall metal pipe are used for vent con-nectors, the common vent must be sized usingTable 4.
31) Locate draft hood outlet or flue collar of small-est input appliance closest to or under commonvent.
32) When vent table permits more than one diam-eter of pipe to be used for a connector or vent,the smallest permitted diameter should bepreferred.
TYPICAL VENTING APPLICATIONS
FIGURE 3
Table 1 should be used when Type B vent is used for both the vent connector and the vertical vent.
VENT
VENT CONNECTOR
D
HL
FIGURE 4
Table 2 should be used when a single-wall metal vent connector is attached toType B vertical vent.
VENT
VENT CONNECTOR
D
HL
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FIGURE 5
Table 3 should be used when Type B vent connectors are attached to a Type B common vent.
TYPE B COMMON VENT
APPLIANCE 1 APPLIANCE
2
D2
D1
H
R2
R1
APPLIANCE 1 APPLIANCE
2
H
R1R2
D
L
Schematic Diagram showing a typical manifolded common vent section “L” of the vent connector. (See Note 5)
“L” Less than or equal to 1.5 feet x D
FIGURE 7
APPLIANCE 1 APPLIANCE
2
H
R1R2
D
L
Schematic Diagram showing offset in the common vent section of the vertical vent. (See Note 6)
FIGURE 8
FIGURE 6
Table 4 should be used when single-wall metal vent connectors are attached to a Type B common vent.
TYPE B COMMON VENT
APPLIANCE 1 APPLIANCE
2
D2
D1
H
R2
R1
7
FIGURE 9
Table 5 shall be used when a Type B, double- wall vent connector is attached to a tile lined masonry chimney.
TILE-LINED MASONRY CHIMNEY
VENT CONNECTOR
A
L
D
H
FIGURE 12
Table 8 shall be used when single-wall metal vent connectors are attached to a tile lined masonry chimney.
TILE-LINED MASONRY CHIMNEY
A
D
D
H
RR
FIGURE 10
Table 6 shall be used when a single-wall metal vent connector is attached to a tile lined masonry chimney.
TILE-LINED MASONRY CHIMNEY
VENT CONNECTOR
A
L
D
H
FIGURE 11
Table 7 shall be used when Type B double-wall vent connectors are attached to a tile lined masonry chimney.
TILE-LINED MASONRY CHIMNEY
A
D
D
H
RR
8
VENT TABLES
Capacity of Type B Double-Wall Vents with Type B Double-Wall ConnectorsServing a Single Category I Appliance
TABLE 1
Height aLateralH a aa L
(ft) aa(ft)
Vent and Connector Diameter - D (inches)
3˝ 4˝ 5˝ 6˝ 7˝ 8˝ 9˝
Appliance Input Rating in Thousands of Btu Per Hour
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
0132125
78514946
46363432
0183036
152979491
86676461
0273947
251157153149
141105103100
0325059
375232227223
205157153149
0446678
524321316310
285217211205
0537993
698425419413
370285279273
06393
110
897543536530
470370362354
8 0258
0122328
84575349
50403835
0163239
16510910398
94757166
0254251
276178171164
155120115109
0285364
415263255247
235180173165
0427084
583365356347
320247237227
0508399
780483473463
415322313303
06099
117
1006619607596
537418407396
10 02510
0122330
88615751
53424036
0173241
175118113104
100817770
0234154
295194187176
166129124115
0265267
447289280267
255195188175
0406888
631402392376
345273263245
04881
104
847533522504
450355346330
05795
122
1096684671651
585457446427
15 0251015
011222935
9469655953
5848454137
015304048
191136130121112
11293878276
020395161
327226219206195
187150142135128
022496476
502339330315301
285225217208198
038648498
716475463445429
390316300288275
0457699
115
970633620600580
525414403386373
05390
116134
1263815800777755
682544529507491
20 025101520
01021283448
977571645852
615148444035
01429384655
202149143133124116
11910096898478
01838505969
349250242229217206
202166160150142134
02047627384
540377367351337322
307249241228217206
033628194
107
776531519499481464
430346337321308295
0417395
111125
1057711697675654634
575470460443427410
05086
112129145
1384917902877853830
752612599576557537
30 02510152030
09
21273356
NR
1008177706458
NR
64565450
NRNRNR
0132837445373
213166160150141132113
1281121081029690
NR
0143648576688
374283275262249237214
220185176171163154NR
01845597080
104
587432421405389374346
336280273261249237219
027587790
102131
853613600580560542507
475394385371357343321
0336991
105119149
1173826811788765743702
650535524507490473444
04282
107124139171
15481072105510281002977929
855700688668648628594
50 02510152030
08
202659
NRNR
10186827670
NRNR
6761
NRNRNRNRNR
0112735425069
216183177168158149131
134122119114NRNRNR
0143545546384
397320312299287275250
232206200190180169NR
0154356667699
633497487471455440410
363314308298288278259
02255738597
123
932715702681662642605
518445438426413401376
0266586
100113141
1297975960935911888844
708615605589572556522
03377
101117131161
1730127612591230120311761125
952813798773747722670
100 0251015203050
NRNRNRNRNRNRNRNR
NRNRNRNRNRNRNRNR
NRNRNRNRNRNRNRNR
01026334047
NRNR
218194189182174166NRNR
NRNRNRNRNRNRNRNR
0123343505978
NR
407354347335321311290NR
NRNRNRNRNRNRNRNR
0134053627192
147
665566557542528513483428
400375369361353344NRNR
01852688090
115180
997831820801782763726651
560510504493482471449405
021608093
105131197
1411115511411118109510731029944
770700692679666653627575
0257194
109122149217
19081536151914921465143813871288
1040935926910895 880849787
9
VENT TABLES
Capacity of Type B Double-Wall Vents with Type B Double-Wall ConnectorsServing a Single Category I Appliance
TABLE 1 (Cont’d)
Height aLateralH a aa L
(ft) a a(ft)
Vent and Connector Diameter - D (inches)
10˝ 12˝ 14˝ 16˝ 18˝ 20˝ 22˝ 24˝
Appliance Input Rating in Thousands of Btu Per Hour
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
075
110128
1121675668661
570455445435
0103147171
1645982975967
850650640630
0138191219
2267134613381330
1170890880870
0178242276
2983176917611753
1530117011601150
0225300341
3802225022422235
1960148014751470
0296390437
4721278227742767
2430185018351820
0360469523
5737337733703363
2950222022152210
0426555618
6853403040234017
3520267026602650
8 0258
071
115137
1261770758746
660515503490
098
154180
1858112411101097
970745733720
0130199231
2571154315281514
1320102010101000
0168251289
3399203020132000
1740134013301320
0212311354
4333258425632552
2220170016851670
0278398450
5387319631803163
2750211020902070
0336476537
6555388238633850
3360256025452530
0401562630
7838463446124602
4010305030403030
10 02510
068
112142
1377852839817
720560547525
093
149187
2036124412291204
1060850829795
0124192238
2825171316961669
1450113011051080
0161243298
3742225622382209
1925148014611430
0202300364
4782286828492818
2450189018711840
0264382459
5955355635363504
3050234023182280
0319458546
7254432243014268
3710284028182780
0378540641
8682515351325099
4450339033713340
15 0251015
063
105135155
159610191003977953
840675660635610
086
140177202
23801495147614461418
1240985967936905
0114182227257
33232062204120091976
17201350132712891250
0147229283318
44232719269626592623
22701770174817121675
0186283346385
56783467344234023363
29002260223521932150
0239355432479
70994304427842344192
36202800277727392700
0290426510564
86655232520451595115
44103410338533433300
0346501599665
103936251622261756129
53004080405740193980
20 025101520
059
101130150167
175611501133110510781052
930755738710688665
081
135172195217
263716941674164116091578
13501100107910451018990
0107174220248273
370123432320228222452210
190015201498146014251390
0139219273306335
494830973071302929882948
252020001978194019101880
0175270334372404
637639553926388038353791
325025702544250024652430
0220337413459495
798849164885483547864737
406032003174313030903050
0269403489541585
978559835950589658445792
498039103880383037953760
0321475573631689
1175371547119706370076953
600047004662460045754550
30 02510152030
05496
125143160195
1977135113321301127212431189
1060865851829807784745
074
127164187207246
3004200419811944190818731807
1550131012891254122011851130
098
164209237260305
4252278627592716267426332555
2170180017751733169216501585
0127206259292319369
5725369636663617357035233433
2920238023502300225022002130
0159252316354384440
7420473447014647459445424442
3770305030202970292028702785
0199312386431467540
9341590058635803574456865574
4750381037833739369536503565
0241373456507548635
11483719471557090702669646842
5850465046224574452744804375
0285439535590639739
13848861785748505843783708239
7060560055525471539153105225
50 02510152030
04190
118136151183
2231162016001567153615051446
11951010996972948924876
066
118154177195232
3441243124062366232722882214
1825151314951466143714081349
086
151196222244287
4934340933803332328532393150
2550212521022064202619871910
0113191243274300347
6711455445204464440943564253
3440284028132767272126752631
0141234295330361412
8774586458265763570156415523
4460367036393585353434813431
0171283355396433494
11129733972957224715570866953
5635463045974542451144794421
0209336419465506577
13767898089338855877987048557
6940569556545585554655065444
0251394491542586672
16694107881073710652105701048810328
8430686068186749671066706603
100 0251015203050
03082
108126141170241
24911975195519231892186118021688
13101170115911421124110710711000
044
107142163181215292
39253027300229612920288028032657
20501820180317751747171916631550
072
136180206226265350
57294313428242314182413340373856
29502550253125002469243823752250
095
172223252277319415
79145834579757375678561955055289
40503500347534343392335132673100
0120208268304330378486
104857591754874787409734172096956
53004600456645094451439442794050
0138245318358387446572
134549577952894479367928991368841
67005800576957175665561355095300
0169293374418452514659
1681711803117481165811569114821131010979
86007200716271007037697568506600
0204341436487523592752
2057814264142041410514007139101372013354
103008800875686838610853783918100
10
VENT TABLES
Capacity of Type B Double-Wall Vents with Single-Wall Metal ConnectorsServing a Single Category I Appliance
TABLE 2
Height aLateral
H aa a L
(ft)
a a
(ft)
Vent and Connector Diameter - D (inches)
3˝ 4˝ 5˝ 6˝ 7˝ 8˝ 9˝ 10˝ 12˝
Appliance Input Rating in Thousands of Btu Per Hour
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
3839
NRNR
7751
NRNR
45363331
59607483
151969289
85666360
8585
102114
249156152147
14010410299
126123146163
373231225220
204156152148
165159187207
522320313307
284213208203
211201237263
695423416409
369284277271
267251295327
894541533526
469368360352
371347409449
1118673664656
569453443433
537498584638
1639979971962
849648638627
8 0258
3739
NRNR
8356
NRNR
50393733
58597790
16410810295
93756964
8383
107122
273176168161
154119114107
123121151175
412261252243
234179171163
161155193223
580363352342
319246235225
206197245280
777482470458
414321311300
258246305344
1002617604591
536417404392
360339418470
1257768754740
658513500486
521486598665
1852112011041089
967743730715
10 02510
373952
NR
876156
NR
53413934
57597697
174117111100
99807668
8282
105132
293193185171
165128122112
120119148188
444287277261
254194186171
158153190237
628400388369
344272261241
202193241296
844531518497
449354344325
253242299363
1093681667643
584456443423
351332409492
1373849834808
718559544520
507475584688
2031124212241194
1057848825788
15 0251015
363851
NRNR
936963
NRNR
57474439
NR
56577595
NR
190136128116NR
11193867972
8080
102128158
325225216201186
186149140131124
116115144182220
499337326308290
283224217203192
153148182228272
713473459438418
388314298284269
195187231284334
966631616592568
523413400381367
244232287349404
1259812795768742
681543526501484
336319392470540
15911015997966937
838673657628601
488457562664750
23741491146914331399
1237983963928894
20 025101520
353750
NRNRNR
967468
NRNRNR
60504741
NRNR
54567393
NRNR
200148140129NRNR
11899948680
NR
7878
100125155186
346248239223208192
201165158146136126
114113141177216254
537375363344325306
306248239224210196
149144178222264309
772528514491469448
428344334316301285
190182224277325374
1053708692666640616
573468457437419400
238227279339393448
1379914896866838810
750611596570549526
326309381457526592
175111461126109210601028
927754734702677651
473443547646730808
263116891665162615871550
13461098107410371005973
30 02510152030
343749
NRNRNRNR
998074
NRNRNRNR
635652
NRNRNRNR
53557291
115NRNR
211164157144131NRNR
12711110698
NRNRNR
767698
122151181NR
372281271255239223NR
219183173168157NRNR
110109136171208246NR
584429417397377357NR
334279271257242228NR
144139171213255298389
849610595570547524477
472392382367349333305
184175215265312360461
1168823806777750723670
647533521501481461426
229219269327379433541
1542106910491017985955895
852698684662638615574
312296366440507570704
1971134613241287125112161147
1056863846821794768720
454424524620702780937
2996199919711927188418411759
1545130812831243120511661101
50 02510152030
333648
NRNRNRNR
998480
NRNRNRNR
6661
NRNRNRNRNR
51537089
112NRNR
213181174160148NRNR
133121117NRNRNRNR
737394
118145176NR
394318308292275257NR
230205198186174NRNR
105104131162199236315
629495482461441420376
361312305292280267NR
138133164203244285373
928712696671646622573
515443435420405389NR
176168204253299345442
1292971953923894866809
704613602583562543502
220209257313363415521
1724127312521217118311501086
948811795765736708649
295280347418481544674
2223161515911551151214731399
11891007991963934906848
428401496589668741892
3432242623962347229922512159
1818150914901455142113871318
100 0251015203050
NRNRNRNRNRNRNRNR
NRNRNRNRNRNRNRNR
NRNRNRNRNRNRNRNR
49516785
132NRNRNR
214192186175162NRNRNR
NRNRNRNRNRNRNRNR
697090
113138168231NR
403351342324310295264NR
NRNRNRNRNRNRNRNR
10098
125153188224301NR
659563551532511487448NR
395373366354343NRNRNR
131125156191230270355540
991828813789764739685584
555508501486473458NRNR
166158194238281325418617
140411521134110410751046988866
765698688672656639NRNR
207196240293342391491711
19001532151114771443141013431205
1033933921902884864824NR
273259322389447507631895
24791970194519051865182517471591
1300116811531133111010871041
NR
395371460547618690834
1138
39123021299029382888283827392547
20421817179617631730169616271489
11
VENT TABLES
Capacity of Type B Double-Wall Vents with Type B Double-Wall ConnectorsServing Two or more Category I Appliances
TABLE 3
Vent Connector Capacity
Common Vent Capacity
VentHeight
H(ft)
ConnectorRise
R(ft)
Vent Connector Diameter - D (inches)
3˝ 4˝ 5˝ 6˝ 7˝ 8˝ 9˝ 10˝
Appliance Input Rating Limits in Thousands of Btu Per Hour
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 123
222324
374144
263135
353738
667581
465562
464849
106121132
728696
586062
164183199
104124139
777982
225253275
142168189
929597
296333363
185220248
109112114
376424463
237282317
128131134
466526575
289345386
8 123
222324
404447
273236
353637
728087
485764
495153
114128139
7690
101
646667
176195210
109129145
848688
243269290
148175198
100103105
320356384
194230258
118121123
408454492
248294330
138141143
507564612
303358402
10 123
222324
434750
283337
343637
788692
505967
495152
123136146
7893
104
656769
189206220
113134150
899194
257282303
154182205
106109111
341374402
200238268
125128131
436479515
257305342
146149152
542596642
314372417
15 123
212224
505355
303540
333536
8996
102
536371
474951
142153163
8399
111
646668
220235248
120142160
889193
298320339
163193218
110112115
389419445
214253286
134137140
493532565
273323365
162165167
609658700
333394444
20 123
212223
545760
313742
333435
99105110
566674
464850
157167176
87104116
626466
246259271
125149168
868991
334354371
171202228
107110113
436463486
224265300
131134137
552587618
285339518
158161164
681725764
347414466
30 123
202122
626466
333944
313334
113118123
597079
454748
181190198
93110124
606264
288299309
134158178
838588
391408423
182215242
103105108
512535555
238282317
125129132
649679706
305360405
151155158
802840874
372439494
50 123
192122
717375
364348
303233
133137141
647686
434546
216223229
101119134
575961
349358366
145172194
788183
477490502
197234263
97100103
627645661
257306343
120123126
797820842
330392441
144148151
98410141043
403478538
100 123
181920
828384
374450
283031
158161163
667989
404244
262267272
104123138
535557
442447452
150178200
737578
611619627
204242272
919497
810822834
266316355
112115118
103810541069
341405455
135139142
128513061327
417494555
VentHeight
H(ft)
Common Vent Diameter - D (inches)
4˝ 5˝ 6˝ 7˝ 8˝ 9˝ 10˝
Combined Appliance Input Rating in Thousands of Btu Per Hour
When liner sizes differ dimensionally from those shown in Table 9equivalent diameters may be determined from published tables forsquare and rectangular ducts of equivalent carrying capacity or byother engineering methods.
NOMINALLINER SIZE
INCHES
INSIDEDIMENSIONS INLINER INCHES
INSIDE DIA.OR EQUIVALENT
DIA. INCHES
EQUIVALENTAREA
SQ. INCHES4 x 8 2 1/2 x 6 1/2 4
567
12.219.6 28.338.3
8 x 8 6 3/4 x 6 3/4 7.48
42.750.3
8 x 12 6 1/2 x 10 1/2 910
63.6 78.5
12 x 12 9 3/4 x 9 3/4 10.411
83.3 95
12 x 16 9 1/2 x 13 1/2 11.81214
107.5113
153.916 x 16 13 1/4 x 13 1/4 14.5
15162.9176.7
16 x 20 13 x 17 16.218
206.1254.4
20 x 20 16 3/4 x 16 3/4 18.220
260.2314.1
20 x 24 16 1/2 x 20 1/2 20.122
314.2380.1
24 x 24 20 1/4 x 20 1/4 22.124
380.1452.3
24 x 28 20 1/2 x 24 1/4 24.1 456.228 x 28 24 1/4 x 24 1/4 26.4
27543.3572.5
30 x 30 25 1/2 x 25 1/2 27.930
607706.8
30 x 36 25 1/2 x 31 1/2 30.933
749.9855.3
36 x 36 31 1/2 x 31 1/2 34.436
929.41017.9
19
Example 1:
Single Draft-Hood-Equipped Appliance
Suppose that an installer has a 120,000 Btu/hr input appli-ance with a 5 inch diameter draft hood outlet that needs tobe vented into a 10 foot high Type B vent system. Whatsize vent should be used assuming (a) a 5-Ft lateral sin-gle-wall metal vent connector is used with two 90
°
elbows,(b) a 5-Ft lateral single-wall metal vent connector is usedwith three 90
°
elbows in the vent system?
Solution
Table 2 should be used to solve this problem because sin-gle-wall metal vent connectors are being used with a TypeB vent: Refer to Figure 4 of Typical Applications.
(a) Read down the first column in Table 2 until the row associated with a 10-Ft height and a 5-Ft lateral is found. Read across this row until a vent capacity greater than 120,000 Btu/hr is located in the shaded columns labeled “NAT Max” for draft-hood-equipped appliances. In this case, a 5 inch diameter vent has a capacity of 122,000 Btu/hr and may be used for this application.
(b) If three 90
°
elbows are used in the vent system, then the maximum vent capacity listed in the tables must be reduced by 10 percent (see Note 3). This implies that the 5 inch diameter vent has an adjusted capacity of only 110,000 Btu/hr. In this case, the vent system must be increased to 6 inches in diameter. See calculations below:
122,000 x .90 = 110,000 for 5˝ Vent
From Table 2—Select 6˝ Vent 186,000 x .90 = 167,000; This is greater than the required120,000, therefore use a 6˝ Vent and connector whenthree elbows are used.
10′
5′
EXAMPLE 1
DRAFT HOOD EQUIPPED APPLIANCE 120,000 BTUH INPUT
B-VENT
ELBOW
SINGLE WALL
Example 2: Single Fan-Assisted Appliance
Suppose an installer has an 80,000 Btu/hr input fan-assisted appliance that must be installed using 10 feet oflateral connector attached to a 30-Ft high Type B vent.Two 90° elbows are needed for the installation. Can a sin-gle-wall metal vent connector be used for this application?
Solution
Table 2 refers to the use of single-wall metal vent connec-tors with Type B vent. In the first column find the row asso-ciated with a 30-Ft height and a 10-Ft lateral. Read acrossthis row, looking at the “FAN Min” and “FAN Max” columns,to find that a 3 inch diameter single-wall metal connectorvent is not recommended. Moving to the next larger sizesingle wall connector (4˝) we find that a 4 inch diametersingle-wall metal connector has a recommended minimumvent capacity of 91,000 Btu/hr and a recommended maxi-mum vent capacity of 144,000 Btu/hr. The 80,000 Btu/hrfan-assisted appliance is outside this range, so we con-clude that a single-wall metal vent connector cannot beused to vent this appliance using 10 feet of lateral for theconnector.
However, we see that if the 80,000 Btu/hr input appliancecould be moved to within 5 feet of the vertical vent, then a4 inch single-wall metal connector could be used to ventthe appliance. Table 2 shows the acceptable range of ventcapacities for a 4 inch vent with 5 feet of lateral to bebetween 72,000 Btu/hr and 157,000 Btu/hr.
If the appliance cannot be moved closer to the vertical vent,then Type B vent could be used as the connector material.In this case, Table 1 shows that for a 30-Ft high vent with 10feet of lateral, the acceptable range of vent capacities for a4 inch diameter vent attached to a fan-assisted applianceare between 37,000 Btu/hr and 150,000 Btu/hr.
30′
10′ LATERAL
EXAMPLE 2
FAN ASSISTED APPLIANCE 80,000 BTUH INPUT
EXAMPLES USING SINGLEAPPLIANCE VENTING TABLES
20
Example 3:
Common Venting Two Draft-Hood Appliances
Suppose a 35,000 Btu/hr water heater is to be commonvented with a 150,000 Btu/hr furnace using a commonvent with a total height of 30 feet. The connector rise is 2feet for the water heater and 3 feet for the furnace.Assume single-wall metal connectors will be used withType B vent. What size connectors and combined ventshould be used in this installation?
Solution
—(Table 4 applies in this example)
Table 4 should be used to size single-wall metal vent con-nectors attached to Type B vertical vent. In the vent con-nector capacity Table 4, find the row associated with a 30-Ft vent height. For a 2-Ft rise on the vent connector for thewater heater, read the shaded columns for draft-hood-equipped appliances to find that a 3 inch diameter ventconnector has a capacity of 37,000 Btu/hr.
Therefore, a 3 inch single-wall metal vent connector maybe used with the water heater. For a draft-hood-equippedfurnace with a 3-Ft rise, read across the appropriate row tofind that a 5 inch diameter vent connector has a maximumcapacity of 120,000 Btu/hr (which is too small for the fur-nace) and a 6 inch diameter vent connector has a maxi-mum vent capacity of 172,000 Btu/hr. Therefore, a 6 inchdiameter vent connector should be used with the 150,000Btu/hr furnace.
For the capacity of the combined vent, the lower portion ofTable 4 should be used. The combined vent capacityrequired is 185,000 Btu/hr. Table 4 shows that the com-bined vent capacity of a 6 inch diameter vent with a 30-Ftvent height is 257,000 Btu/hr. This is more than adequateto handle the 35,000 Btu/hr input water heater and the150,000 Btu/hr input furnace.
2′
3′
30′
Combined Capacity 35,000 + 150,000 = 185,000
EXAMPLE 3
DRAFT HOOD EQUIPPED WATER HEATER
35,000 BTUH INPUT
DRAFT HOOD EQUIPPED FURNACE 150,000 BTUH INPUT
ASSUME B VENT
SINGLE WALL CONNECTOR
Example 4: Common Venting a Draft Hood Water Heater with a Fan-Assisted Furnace
In this case, a 35,000 Btu/hr input draft-hood-equippedwater heater with a 2 foot connector rise is to be commonvented with a 100,000 Btu/hr fan-assisted furnace with a3-Ft connector rise. The common vent consists of a 30-Ftrise of Type B vent. What are the recommended ventdiameters for each connector and the common vent?
Solution—(Table 4)
Water Heater Vent Connector Diameter. Let us assumethe installer would like to use a single-wall metal vent con-nector. Using Table 4, Vent Connector Capacity, readdown the Total Vent Height “H” column to 30 feet and readacross the 2-Ft Connector Rise “R” row to the first Btu/hrrating in the “NAT Max” column that is equal to or greaterthan the water heater input rating. The table shows that a 3inch vent connector has a maximum input rating of 37,000Btu/hr. Since this is greater than the water heater input rat-ing, a 3 inch vent connector is adequate. Furthermore,since the water heater is equipped with a draft hood, thereare no minimum input rating restrictions.
Furnace Vent Connector Diameter.
Again, let us assumethe installer would like to use a single-wall metal vent con-nector. Using Table 4, Vent Connector Capacity, read downthe Total Vent Height “H” column to 30 feet and across the3-ft Connector Rise “R” row. Since the furnace has a fan-assisted combustion system, find the first “FAN Max” col-umn with a Btu/hr rating greater than the furnace input rat-ing. The 4 inch vent connector has a maximum input ratingof 119,000 Btu/hr and a minimum input rating of 85,000 Btu/hr. The 100,000 Btu/hr furnace in this example falls withinthis range, so a 4 inch connector is adequate. If the furnacewould have had an input rating of 80,000 Btu/hr, then aType B vent connector (see Table 4) would have to be usedin order to meet the minimum capacity limit.
2′
3′
30′
EXAMPLE 4
WATER HEATER 35,000 BTUH INPUT
FAN ASSISTED FURNACE
100,000 BTUH INPUT
TYPE B
SINGLE WALL CONNECTORS
EXAMPLES USING COMMONVENTING TABLES
21
Example 4:
(cont’d)
Common Vent Diameter.
The total input to the commonvent is 135,000 Btu/hr. Using Table 4, Common VentCapacity, read down the Total Vent Height “H” column to30 feet and across this row to find the smallest vent diame-ter in the “FAN+NAT” column that has a Btu/hr rating equalto or greater than 135,000 Btu/hr. The 4 inch common venthas a capacity of 132,000 Btu/hr and the 5 inch commonvent has a capacity of 202,000 Btu/hr. Therefore, the 5inch common vent should be used in this example.
Summary.
In this example, the installer may use a 3 inchdiameter, single-wall metal vent connector for the waterheater and a 4 inch diameter, single-wall metal vent con-nector for the furnace. The common vent should be a 5inch diameter Type B vent
Example 5:
Single Draft Hood Equipped Furnace Vented into a Masonry Chimney
A 135,000 Btu/hr draft hood equipped furnace is to bevented into a 15´ high tile lined masonry chimney. Thechimney is not exposed to the outside except above theroof line. The furnace has a 6˝ diameter draft hood outletand requires a 10´ lateral vent connector with 3 elbows.The chimney is constructed using a 8˝ x 8˝ liner. What sizesingle wall vent connector is required?
Solution:
Table 6 should be used. Refer to the figure for Example 5.
EXAMPLE 5
TILE-LINED MASONRY CHIMNEY
VENT CONNECTOR WITH THREE
ELBOWS
8″ x 8″
10′
D
15′
DRAFT HOOD EQUIPPED FURNACE
To determine the required vent connector diameter, readdown the height column in Table 6 until 15´ is found. Findthe row for a 10´ long lateral. The table shows that a 6˝diameter connector will allow a maximum capacity of151,000 Btu/hr for “Nat Max.” (draft-hood equipped) fur-nace. Because 3 elbows are required, however, the maxi-mum capacity must be reduced by 10% (See Note 3).Allowing for the additional elbow the corrected maximumcapacity is 135,900 Btu/hr. A 6˝ diameter connector islarge enough and should be used. The internal area of thechimney is 8˝ x 8˝ = 64 sq. in. and is within the acceptablerange (38 sq. in. to 198 sq. in.) for a 6˝ vent connector asshown in Table 6.
Example 6: Common Venting into a Masonry Chimney
In this case, a 35,000 Btu/hr input 4 inch diameter outletdraft hood-equipped water heater with 2 feet of connectorrise and 4 feet of horizontal length is to be common ventedwith a 100,000 Btu/hr fan-assisted furnace with a 4 inchdiameter flue collar, 3 feet of connector rise and 6 feet ofhorizontal length. The common vent is an 8 x 12 tile linedchimney that is 30 feet tall. What are the recommendedvent diameters for each connector? Is this an acceptableinstallation?
Solution:
Table 8 is used to size common venting installationsinvolving single wall connectors into masonry chimneys.
Water Heater Vent Connector Diameter. Using Table 8,Vent Connector Capacity, read down the Total Vent Height“H” column to 30 feet and read across the 2 ft ConnectorRise “R” row to the first Btu/hr rating in the “NAT MAX” col-umn that is equal to or greater than the water heater inputrating. The Table shows that a 3 inch vent connector has amaximum input of only 31,000 Btu/hr while a 4 inch ventconnector has a maximum input of 57,000 Btu/hr. A 4 inchvent connector must therefore be used.
Furnace Vent Connector Diameter. Using Table 8 VentConnector Capacity, read down the Total Vent Height “H”column to 30 feet and across the 3 ft Connector Rise “R”row. Since the furnace has a fan-assisted combustion sys-tem, find the first “FAN MAX” column with a Btu/hr ratinggreater than the furnace input rating. The 4 inch vent con-nector has a maximum input rating of 127,000 Btu/hr and aminimum input rating of 95,000 Btu/hr. The 100,000 Btu/hrfurnace in this example falls within this range, so a 4 inchconnector is adequate.
EXAMPLES USING COMMONVENTING TABLES
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EXAMPLE 6:
(cont’d)
Masonry Chimney.
From Table 9, the Equivalent Area fora Nominal Liner size of 8 inches x 12 inches is 63.6 squareinches. Using Table 8, Common Vent Capacity, read downthe “Fan + Nat” column under the Minimum Internal Areaof Chimney value of 63 to the row for 30-ft height, to find acapacity value of 739,000 Btu/hr. The combined input rat-ing of the furnace and water heater 135,000 Btu/hr, is lessthan the Table value, so this is an acceptable installation.
Note 19 requires the common vent area to be no greaterthan seven times the flow area of the smallest applianceoutlet area. Both appliances in this installation use 4 inchdiameter outlets. From Table 9, the Equivalent Area for anInside Diameter of 4 inches is 12.2 square inches. Seventimes 12.2 is 85.4, which is greater than 63.6, so this con-figuration is acceptable.
Note 1 specifies that the Table values are for vents orchimneys which are not exposed to the outdoors below theroofline. If the masonry chimney in this case were exposedbelow the roofline, then the appliance manufacturer, localgas utility, and/or authority having jurisdiction must be con-sulted.
EXAMPLE 7:
Interpolating Between Table Values
An installer has an 80,000 Btu/hr input appliance with a 4inch diameter draft hood outlet that needs to be ventedinto a 12-ft high Type B vent. The vent connector has a 5 ftlateral length and is also Type B. Can this appliance bevented using a 4 inch diameter vent?
Solution
Table 1 is used in the case of an all Type B vent system.However, since there is no entry in Table 1 for height of 12feet, interpolation must be used. Read down the 4 inchdiameter “NAT Max” column to the row associated with 10ft. height and 5 ft. lateral to find the capacity value of77,000 Btu/hr. Go down further to the 15 ft. height, 5 ft. lat-eral row to find the capacity value of 87,000 Btu/hr. The dif-ference between the 15 ft. height capacity value and the10 ft. height capacity value is 10,000 Btu/hr. The capacityfor a vent system with a 12 ft. height is equal to the capac-ity for a 10 ft. height plus 2/5 of the difference between the10 ft. and 15 ft. height values, or 77,000 + 2/5 x 10,000 =81,000 Btu/hr. Therefore, a 4 inch diameter vent may beused in the installation.
23
Rise
Other Inputs From Below
• Common Vent Size Based on All Inputs Entering This Segment
and Available Total Height • Available Total Height “H” Equals Rise Plus
Distance Between Tees
Vent Connector Size Depends On: • Input • Rise • Available Total Height “H” • Table 3 Connectors
Common Vent Size Depends On: • Combined Inputs • Available Total Height “H” • Table 3 Common Vent • Vertical Common Vent With No Offsets
• Total Input
Tee Same Size as Segment Above
Increase Vent
Connector Size If
Necessary
Multi-story Gas Vent Design Procedure for Each Segment of System
Design Vent Connector for First Floor Appliance as an Individual Vent of This Total Height for Input of First Floor Appliance
Each Interconnection Tee is Same Size as Segment of Common Vent Directly Above
✽
Principles of Design of Multi-story Vents Using Vent Connector and Common Vent Design Tables
Available Total Height for Second Floor Appliance
Use Vent Connector Table
Rise
Multi-story Vent System
4
3
Available Total Height for Third Floor Appliance
Rise
Available Total Height for Top
Floor Appliance
Rise
Figure 14
2
1
Tee With Cap Optional
Listed Cap
Third Connection Tee ✽
Second Connection Tee ✽
First Connection Tee ✽
Top Floor Appliance
Use Vent Connector Table
Third Floor Appliance
Use Vent Connector Table
Second Floor Appliance
First Floor Appliance
Use Available Total Height for Second Floor Appliance and Combined Heat Input of Two Appliances
Use Individual Ventfor Top Floor Appliance if Connector Requirement for Rise or Total Height Cannot be Met
Available Total Height for Third Floor Appliance and Combined Input of Three Appliances (If Top Floor Appliance is Not Connected, Measure Total Height to Vent Top)
Use Available Total Height for Top Floor Appliance and Combined Input of All Appliances on Common Vent