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Chimney/Vent Sizing Tables & Formulas
- Size specification requirements for chimney flues and vents - diameter, height, etc.
- Flue diameter and height requirements for Category I Draft Hood and Fan Assisted Appliances
- "Smoke pipe" diameter sizes vs. BTUs or BTU venting requirements
- Table of B-vent sizes vs. BTU input maximum ratings
- 6 Factors that determine the required chimney/vent diameter for a given BTUH capacity
- Why is a rectangular or square chimney flue clay tile liner translated into "round flue" equivalent square inches when determing chimney BTUH capacity?
- Chimney flue size requirements for fireplaces, boilers, furnaces, water heaters, coal stoves
- Questions & Answers about size requirements for chimney flues
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
This article describes the size requirements for chimney flues for different categories of heating appliances. We include excerpts from UMC tables along with additional commentary to assist in sizing metal or masonry chimneys according to chimney diameter, height, materials, and the input BTUH of the appliance(s) to be vented. .
As with most building nspection and safety topics, this material may be incomplete. Check with your local building code officials for local building code requirements when designing, building, or installing chimneys and vents.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Sizing of Chimney Flues, Flues, Vents - Category I Draft Hood and Fan Assisted Appliances
The old sheet metal workers rule of thumb was to size the chimney flue by
taking the
square root of the sum of the squares of the appliance draft hood
diameters
i.e.: a 3" plus a 4" appliance vent will require a 5" flue. ( 32 + 42 = 25.
The square root of 25 = 5.)
NFPA 1992 (7.5.3) states that draft hood appliances, Category I
appliances and other appliances that use Type B vents must have a
chimney
flue area not less than the area of the largest vent outlet plus 50% of the area of
the additional flue outlet.
The following calculation works out to be the same
answer as the "Rule of Thumb" sizing, i.e.: (4/22 x 3.14 = 12.56) + (3/22 x 3.14/2 =
3.53) = 16.09 / 3.14 = 5.1251/2 = 2.26 x 2 = 4.52" or 5".
The 1992 GAMA vent sizing tables for single-wall metal vent connectors
attached to a tile lined masonry chimney uses Table 8. The result of those
calculation using a 38,000 BTU water heater with a 3" draft hood and a 37,500
BTU boiler with a 4" draft hood connected to a 20' high chimney is to use a
common flue with an area of 28 square inches or a 6" flue vs a 5" flue in the
previous examples.
These tables also indicate that a 3" vent is not capable of venting the
38,000 BTU water heater.
A 4" would be required. Also the flow area of the
chimney must not be more that 7 times the area of the smallest vent area.
Therefore, 7 x 7.065 = 49.455 vs 28, a 6 inch flue pipe is ok. The maximum size
flue that could be used is 8 inch at 50.3.
Table of Chimney, Flue, or Vent Size Requirements vs. BTUs of Appliances being Vented
Watch out: you cannot safely choose a chimney flue diameter based only on the BTU input of the appliance(s) being vented. The required size or diameter of a metal chimney such as a B-vent depends on at least the following factors:
- Chimney vent height: The total vent ("smoke pipe" or "chimney") height from the point of connection of the appliance (or its flue vent connector pipe) to the top of the chimney opening (not the top of the chimney cap).
- Flue vent horizontal run: The total lateral or horizontal distance that the vent runs before turning to its vertical rise. The longer the horizontal run the greater chimney height is needed to develop adequate draft. For that reason, in the table below you won't see any long horiontal run data for short chimneys. For example in our first chimney sizing table below, if a chimney's total rise is just 6 ft., then the longest horiztontal run that chimney can support is 5 ft.
In some chimney sizing tables we consider not the horizontal run distance of the flue vent connector but its total rise over its run.
- Flue vent connector type: The use of single-wall (Table C-9-A) vs. double-walll B-Vent (Table C-9-B) of horizontal flue vent connectors ("smoke pipe" between the appliance and its connection to the vertical chimney).
The table below is for appliances connected through a single wall flue vent connector to a Type B Vent chimney. BTU capacities are increased if the flue vent connector is also a type B Double-wall system. [Table C-9-B in the same resource]. [10]
- Input BTUH capacity: The maximum total BTUs of the appliance(s) that will be connected to the chimney
- The number of appliances being vented. The first table below (Table C-9-A) gives chimney sizing data for chimneys serving a single heating appliance. Do not Table C-9-A if multiple heating devices are to be connected to a single vent (chimney).
When multiple heating appliances are connected to a single chimney, a different, more restricted table of chimney size requirements is used (Table C-9-D or Table C-9-E, depending on the flue vent connector material) and the total input BTUH capacity of a given flue diameter and height will be less than that where only a single appliance is used.
An additional restriction applies when a vent (chimney) is venting multiple heating appliances: there is a maximum input BTUH specified not only for the total of all appliances to be connected, but also a maximum input BTUH for any of the individual appliances.
So when selecting a chimney diameter for venting multiple heating appliances through a single vent, for any particular chimney type (Masonry vs. B-vent, for example) you will use two BTUH tables: a table of the maximum individual appliance BTUH and a table of the maximum combined appliances input BTUH.
- The chimney type used. The first two tables illustrated below are for B-Vent double wall metal chimneys, generally used for gas fired heating appliances.
Separate tables of chimney size requirements (Table C-9-C) is needed for masonry chimneys as these have different heating and draft properties. The cross sectional shape of the chimney flue (for example rectangular vs. round) in masonry chimneys also affects its BTU capacity. Insulated metal chimneys require still another table of BTU capacities.
Generally, taller chimneys, larger diameter chimneys, and chimneys that are larger in diameter can support a greater total BTU input load. The UMC table includes data for chimneys up to 12" in diameter and 50 ft. in height but we have restricted our version to typical residential chimney diameters and heights.
Watch out: venting a small, low-BTUH appliance into a chimney of any type (masonry, metal, insulated metal, B-vent, etc) that is too large can be dangerous - the small appliance may be unable to heat the chimney to sufficient temperature to generate sufficient draft to vent the appliance safely. We find this problem in older homes where a residential gas-fired water heater is the sole appliance vented into a large, tall masonry chimney. You will see this restriction illustrated by the blank squares in the lower left corner of the table below.
For typical residential heating appliance BTU capacities, the following table provides examples of B-Vent Chimney (or "smoke pipe") sizing for common single-appliance BTU capacity and is adapted from the 1991 Uniform Mechanical Code.[10]
A Guide to Chimney Sizing Tables for Venting Heating Appliances: Which Chimney Sizing Table to Use
Here is a quick guide to the UMC's chimney sizing & BTUH venting capacity tables when sizing a metal or masonry chimney diameter to match the total input BTUH of the heating appliances (boiler, furnace, water heater) being vented. Note that different chimney sizes are required for venting fireplaces and woodstoves. Masonry fireplace chimney size requirements are at FIREPLACES & HEARTHS.
Chimney Type |
Number of Appliances to be Vented |
Metal B-Vent Chimney (Vent)
Type of Flue Vent Connector:1
|
Single Appliance |
Multiple Appliances |
Which Chimney Flue / Vent Sizing Table to Use |
| Single Wall Flue Vent Connector |
|
|
| Double Wall B-vent Flue Vent Connector1 |
|
|
| Masonry Chimney2 |
|
|
| Single Wall Flue Vent Connector |
|
|
| |
|
|
Notes to the Table:
1. A flue vent connector is the horizontal/sloped metal pipe connecting the heating appliance to the entry point of the chimney. Flue vent connectors and their materials, sizing requirements, & fire clearances are at Flue Vent Connectors - Boilers, Furnaces
At double-wall B-vent chimneys the flue vent connector between the appliance and the chimney entry point may be single-wall metal flue vent connector or it may be a double-wall Type-B flue vent material.
2. At most masonry chimneys the flue vent connector or "stackpipe" or "smokepipe" is single wall metal, though for fire clearance needs it may be amended to use sections of insulated metal chimneys.
Types of metal chimneys and their properties and fire clearances are at Metal Chimneys & Flues. |
Table C-9-A (Excerpts): Single Appliance Venting, B-Vent Chimney Capacities for Venting a Single Heating Appliance where a Single Wall Metal Flue Vent Connector is Used Between the Appliance and the Chimney
BTU Color Coding Note: in the tables below we use colors to indicate where an example-approximate appliance BTUH vent capacity rating falls across various chimney parameter combinations. The Gray color indicates that this chimney height and diameter combination cannot be used.
Total Chimney/Vent Height (ft) |
Lateral (horizontal) Run (ft) |
Table of B-Vent Diameter (inches) for a Single Appliance Chimney |
3 in. |
4 in. |
5 in. |
6 in. |
7 in. |
8 in. |
Comments |
Maximum (single) Appliance BTU Input Rating (thousands of BTUs) |
6 ft. |
0 |
39 |
70 |
116 |
170 |
232 |
312 |
|
2 |
31 |
55 |
94 |
141 |
194 |
260 |
|
5 |
28 |
51 |
88 |
128 |
177 |
242 |
|
8 ft |
0 |
42 |
76 |
126 |
185 |
252 |
340 |
|
2 |
32 |
61 |
102 |
154 |
210 |
284 |
|
5 |
29 |
56 |
95 |
141 |
194 |
264 |
|
10 |
|
49 |
86 |
131 |
180 |
250 |
|
10 ft |
0 |
45 |
84 |
138 |
202 |
279 |
372 |
|
2 |
35 |
67 |
111 |
168 |
233 |
311 |
|
5 |
32 |
61 |
104 |
153 |
215 |
289 |
|
10 |
|
54 |
94 |
143 |
200 |
274 |
|
15 |
|
|
84 |
130 |
186 |
258 |
|
15 ft. |
0 |
49 |
91 |
151 |
223 |
312 |
420 |
|
2 |
39 |
72 |
122 |
186 |
260 |
350 |
|
5 |
|
67 |
110 |
170 |
240 |
325 |
|
10 |
|
|
103 |
158 |
223 |
308 |
|
15 |
|
|
|
144 |
207 |
291 |
|
20 |
|
|
|
|
195 |
273 |
|
20 ft. |
|
101 |
163 |
252 |
342 |
470 |
770 |
|
|
80 |
136 |
210 |
286 |
392 |
641 |
|
|
|
123 |
192 |
264 |
364 |
610 |
|
|
|
|
178 |
246 |
345 |
571 |
|
|
|
|
163 |
228 |
326 |
550 |
|
|
|
|
|
|
306 |
525 |
|
30 ft. |
|
|
183 |
276 |
384 |
529 |
878 |
|
|
|
|
230 |
320 |
441 |
730 |
|
|
|
|
210 |
296 |
410 |
694 |
|
|
|
|
|
274 |
388 |
656 |
|
|
|
|
|
|
366 |
625 |
|
|
|
|
|
|
344 |
596 |
|
|
|
|
|
|
|
540 |
|
Table C-9-B (Excerpts): Single Appliance Venting, B-Vent Chimney Capacities for Venting a Single Heating Appliance where a Double-Wall B-Vent Flue Vent Connector is Used Between the Appliance and the Chimney
Total Chimney/Vent Height (ft) |
Lateral (horizontal) Run (ft) |
Table of B-Vent Diameter (inches) for a Single Appliance Chimney |
3 in. |
4 in. |
5 in. |
6 in. |
7 in. |
8 in. |
Comments |
Maximum (single) Appliance BTU Input Rating (thousands of BTUs) |
6 ft. |
0 |
46 |
86 |
141 |
205 |
285 |
370 |
|
2 |
36 |
67 |
105 |
157 |
217 |
285 |
|
6 |
32 |
61 |
100 |
149 |
205 |
273 |
|
12 |
28 |
55 |
91 |
137 |
190 |
255 |
|
| |
|
|
|
|
|
|
|
8 ft
|
0 |
50 |
94 |
155 |
235 |
320 |
415 |
|
2 |
40 |
75 |
120 |
180 |
247 |
322 |
|
8 |
35 |
66 |
109 |
165 |
227 |
303 |
|
16 |
28 |
58 |
96 |
148 |
206 |
281 |
|
| |
|
|
|
|
|
|
|
10 ft
|
0 |
53 |
100 |
166 |
255 |
345 |
450 |
|
2 |
42 |
81 |
129 |
195 |
273 |
355 |
|
10 |
36 |
70 |
115 |
175 |
245 |
330 |
|
20 |
|
60 |
100 |
154 |
217 |
300 |
|
| |
|
|
|
|
|
|
|
15 ft.
|
0 |
58 |
112 |
187 |
285 |
390 |
525 |
|
2 |
48 |
93 |
150 |
225 |
316 |
414 |
|
15 |
37 |
76 |
128 |
198 |
275 |
373 |
|
30 |
|
60 |
107 |
169 |
243 |
328 |
|
| |
|
|
|
|
|
|
|
20 ft.
|
0 |
61 |
119 |
202 |
307 |
430 |
575 |
|
2 |
51 |
100 |
166 |
249 |
346 |
470 |
|
10 |
44 |
89 |
150 |
228 |
321 |
443 |
|
20 |
35 |
78 |
134 |
206 |
295 |
410 |
|
30 |
|
68 |
120 |
186 |
273 |
380 |
|
| |
|
|
|
|
|
|
|
30 ft.
|
0 |
64 |
128 |
220 |
336 |
475 |
650 |
|
2 |
56 |
112 |
185 |
280 |
394 |
535 |
|
20 |
|
90 |
154 |
237 |
343 |
473 |
|
40 |
|
|
|
200 |
298 |
415 |
|
Table C-9-C (Excerpts): Single Appliance Venting, BTU Capacity of Masonry Chimneys where a Single Wall Metal Flue Vent Connector is Used Between the Appliance and the Chimney
Total Chimney/Vent Height (ft) |
Lateral (horizontal) Run (ft) |
Table of B-Vent Diameter (inches) for a Single Appliance Chimney |
3 in. |
4 in. |
5 in. |
6 in. |
7 in. |
8 in. |
Comments |
Maximum (single) Appliance BTU Input Rating (thousands of BTUs) |
6 ft. |
2 |
28 |
52 |
86 |
130 |
180 |
247 |
|
5 |
|
48 |
81 |
118 |
164 |
230 |
|
| |
|
|
|
|
|
|
|
8 ft
|
2 |
29 |
55 |
93 |
145 |
197 |
265 |
|
5 |
|
51 |
87 |
133 |
182 |
246 |
|
10 |
|
|
79 |
123 |
169 |
233 |
|
| |
|
|
|
|
|
|
|
10 ft
|
2 |
31 |
61 |
102 |
161 |
220 |
297 |
|
5 |
|
56 |
95 |
147 |
203 |
276 |
|
10 |
|
|
86 |
137 |
189 |
261 |
|
15 |
|
|
|
125 |
175 |
246 |
|
| |
|
|
|
|
|
|
|
15 ft.
|
2 |
|
67 |
113 |
178 |
249 |
335 |
|
5 |
|
61 |
106 |
163 |
230 |
312 |
|
10 |
|
|
96 |
151 |
214 |
294 |
|
15 |
|
|
|
138 |
198 |
278 |
|
20 |
|
|
|
|
184 |
261 |
|
| |
|
|
|
|
|
|
|
20 ft.
|
2 |
|
73 |
123 |
200 |
273 |
374 |
|
5 |
|
|
115 |
183 |
252 |
348 |
|
10 |
|
|
|
170 |
235 |
330 |
|
15 |
|
|
|
156 |
217 |
311 |
|
20 |
|
|
|
|
202 |
292 |
|
| |
|
|
|
|
|
|
|
30 ft.
|
2 |
|
|
136 |
215 |
302 |
420 |
|
5 |
|
|
|
196 |
279 |
391 |
|
10 |
|
|
|
|
260 |
370 |
|
15 |
|
|
|
|
|
349 |
|
20 |
|
|
|
|
|
327 |
|
| |
|
|
|
|
|
|
|
Table C-9-D (Excerpts): Multiple Appliance BTU Vent Capacity of Type B Double-Wall Vents where a Double Wall Metal B-Flue Vent Connector is Used Between the Appliance and the Chimney
Watch out: the first portion of Table C-9-D specifies the maximum input BTUH capacity of any individual heating appliance that is to be vented along with other appliances out through a single chimney. The continuation of C-9-D below gives the chimney specifications for the total input BTUH of all of the appliances, combined.
Total Chimney/Vent Height (ft) |
Connector Rise (ft) over its run |
Table of B-Vent Diameter (inches) for a Multiple Appliance Chimney |
3 in. |
4 in. |
5 in. |
6 in. |
7 in. |
8 in. |
Comments |
Maximum [Individual] Appliance BTU Input Rating (thousands of BTUs)
|
6 ft. |
1 |
26 |
46 |
72 |
104 |
142 |
185 |
|
2 |
31 |
55 |
86 |
124 |
168 |
220 |
|
3 |
35 |
62 |
96 |
139 |
189 |
248 |
|
| |
|
|
|
|
|
|
|
8 ft
|
1 |
27 |
48 |
76 |
109 |
148 |
194 |
|
2 |
32 |
57 |
90 |
129 |
175 |
230 |
|
3 |
36 |
64 |
101 |
145 |
198 |
258 |
|
| |
|
|
|
|
|
|
|
10 ft
|
1 |
28 |
50 |
78 |
113 |
154 |
200 |
|
2 |
33 |
59 |
93 |
134 |
182 |
238 |
|
3 |
37 |
67 |
104 |
150 |
205 |
268 |
|
| |
|
|
|
|
|
|
|
15 ft.
|
1 |
30 |
53 |
83 |
120 |
163 |
214 |
|
2 |
35 |
63 |
99 |
142 |
193 |
253 |
|
3 |
40 |
71 |
111 |
160 |
218 |
286 |
|
| |
|
|
|
|
|
|
|
20 ft.
|
1 |
31 |
56 |
87 |
125 |
171 |
224 |
|
2 |
37 |
66 |
104 |
149 |
202 |
265 |
|
3 |
42 |
74 |
116 |
168 |
228 |
300 |
|
| |
|
|
|
|
|
|
|
30 ft.
|
1 |
33 |
59 |
93 |
134 |
182 |
238 |
|
2 |
39 |
70 |
110 |
158 |
215 |
282 |
|
3 |
44 |
79 |
124 |
178 |
242 |
317 |
|
| |
|
|
|
|
|
|
|
| |
|
|
|
|
|
|
|
Table C-9-D (Excerpts Continued): Multi-Appliance BTUH Venting Capacity of Type-B Double-Wall Vents [Chimneys] with Type-B flue vent connectors
This table gives the chimney specifications for the total input BTUH of all of the appliances combined and joined into a single vent when the flue is a Type-B double wall metal chimney and when the flue vent connector (between the appliance and the chimney entry point) is also a Type-B double wall unit.
Common [2 or more heating appliance] Vent Capacity in BTUH |
| Total Vent [Chimney] Height (feet) |
Diameter (inches) of the Commmon Vent [Chimney] |
| |
|
|
|
|
|
|
3 |
4 in |
5 in |
6 in |
7 in |
8 in |
10 in |
6 |
|
65 |
103 |
147 |
200 |
260 |
410 |
8 |
|
73 |
114 |
163 |
223 |
290 |
465 |
10 |
|
79 |
124 |
178 |
242 |
315 |
495 |
15 |
|
91 |
144 |
206 |
280 |
365 |
565 |
20 |
|
102 |
160 |
229 |
310 |
405 |
640 |
30 |
|
118 |
185 |
266 |
360 |
470 |
440 |
40 |
|
131 |
203 |
295 |
405 |
525 |
820 |
| |
|
|
|
|
|
|
|
Table C-9-E (Excerpts) Multi-Appliance BTUH Venting Capacity of Double-Wall B-Vent Chimneys where a single-wall metal vent connector is used between the appliances and the chimney
This two-part table gives the chimney specifications for the total input BTUH of all of the appliances combined and joined into a single vent when the flue is a Type-B double wall metal chimney and when the flue vent connector (between the appliance and the chimney entry point) is a single wall metal component.
Multiple-Appliance Single-Wall Flue Vent Connector Capacity |
Total Vent [Chimney] Height (feet) |
| Flue Vent Connector Total Rise (feet) |
Flue Vent Connector Diameter in Inches |
3 in. |
4 in |
5 in |
6 in |
7 in |
8 in |
| Maximum [Individual] Appliance Input BTUH Rating (Thousands of BTUs) |
6 to 8 Ft
|
1 ft |
21 |
|
|
102 |
|
205 |
2 ft |
28 |
|
|
124 |
|
235 |
3 ft |
34 |
|
|
147 |
|
275 |
| |
|
|
|
|
|
|
15 ft
|
1 ft |
23 |
|
|
117 |
|
240 |
2 ft |
30 |
|
|
134 |
|
265 |
3 ft |
35 |
|
|
155 |
|
298 |
| |
|
|
|
|
|
|
30 ft & up |
1 ft |
25 |
|
|
129 |
|
270 |
2 ft |
31 |
|
|
145 |
|
295 |
3 ft |
36 |
|
|
164 |
|
321 |
| |
|
|
|
|
|
|
Multiple-Appliance Common Vent [Chimney] Capacity - Type B-Vent |
Total Vent [Chimney] Height (feet) |
Diameter (inches) of the Commmon Vent [Chimney] |
4 in |
5 in |
6 in |
7 in |
8 in |
10 in |
12 in |
Maximum Combined Input BTUH (thousands) for All of the Appliances |
6 |
48 |
78 |
111 |
155 |
205 |
320 |
|
8 |
55 |
89 |
128 |
175 |
234 |
365 |
505 |
10 |
59 |
95 |
136 |
190 |
250 |
395 |
560 |
15 |
71 |
115 |
168 |
228 |
305 |
480 |
690 |
20 |
80 |
129 |
186 |
260 |
340 |
550 |
790 |
30 |
|
147 |
215 |
300 |
40 |
650 |
940 |
50 |
|
|
|
360 |
490 |
810 |
1190 |
| |
|
|
|
|
|
|
|
Table C-9-F (Excerpts) Multi-Appliance BTUH Venting Capacity of Masonry Chimneys where a single-wall metal vent connector is used between the appliances and the chimney
This two-part table gives the chimney specifications for the total input BTUH of all of the appliances combined and joined into a single vent when the flue is a masonry chimney and when the flue vent connector (between the appliance and the chimney entry point) is a single wall metal component.
Multiple-Appliance Single-Wall Flue Vent Connector Capacity |
Total Vent [Chimney] Height (feet) |
| Flue Vent Connector Total Rise (feet) |
Flue Vent Connector Diameter in Inches |
3 in. |
4 in |
5 in |
6 in |
7 in |
8 in |
| Maximum [Individual] Appliance Input BTUH Rating (Thousands of BTUs) |
6 to 8 Ft
|
1 ft |
21 |
|
|
100 |
|
200 |
2 ft |
28 |
|
|
123 |
|
231 |
3 ft |
34 |
|
|
142 |
|
269 |
| |
|
|
|
|
|
|
15 ft
|
1 ft |
23 |
|
|
112 |
|
225 |
2 ft |
30 |
|
|
132 |
|
256 |
3 ft |
34 |
|
|
151 |
|
289 |
| |
|
|
|
|
|
|
30 ft & up
|
1 ft |
24 |
|
|
124 |
|
250 |
2 ft |
31 |
|
|
142 |
|
282 |
3 ft |
35 |
|
|
160 |
|
312 |
| |
|
|
|
|
|
|
Multiple-Appliance Common Vent [Chimney] Capacity - Type B-Vent |
Total Vent [Chimney] Height (feet) |
Minimum Inernal Area [horizontal cross section] of the Chimney Flue
(square inches) |
18 in |
28 in |
38 in |
50 in |
78 in |
113 in |
Maximum Combined Input BTUH (thousands) for All of the Appliances |
6 |
45 |
71 |
102 |
142 |
245 |
|
8 |
52 |
81 |
118 |
162 |
277 |
405 |
10 |
56 |
89 |
129 |
175 |
300 |
450 |
15 |
66 |
105 |
150 |
210 |
360 |
540 |
20 |
74 |
120 |
170 |
240 |
415 |
640 |
30 |
|
135 |
195 |
275 |
490 |
740 |
50 |
|
|
|
325 |
600 |
910 |
| |
|
|
|
|
|
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Details About Chimney Cross Sectional Areas and Effecs on Venting Capacity of Masonry Chimneys - Translating Rectangular Chimney Flues to Round Flue Equivalents
The UMC Appendix C Table C9-G, "Masonry Chimney Liner Dimensions with Circular Equivalents" translates square or rectangular chimney flue inside dimensions into an equivalent "round" flue diameter and into equivalent square inches of venting capacity.
Why does this translation matter? The venting capacity of a rectangular or square masonry flue, if translated directly into actual or measured square inches of cross section, is less than a round chimney flue of the same square inches of venting capacity.
For example an 8" x 8" square nominal clay chimney flue tile liner has inside dimensions of 6 3/4" x 6 3/4". Just muliplying these dimensions together (6.75 x 6.75) = 45.56 sq.in. But chimney experts and draft measurements show that in a rectangular flue not all of the cross-sectional area is equally effective in developing draft. The effective square inches of venting area, translated to an equivalent round flue, would be less - or aboutd 42.7 square inches.
So when calculating the venting capacity of a square or rectangular clay chimney flue tile or liner by looking at its cross section, we use the UMC's Table C9-G of "round chimney flue equivalents" to get the effective chimney flue vent cross sectional area before we enter the masonry chimney BTUH venting capacity tables 6-9-C (single wall flue vent connectors and single heating appliances) or 6-9-F (single wall flue vent connectors and multiple appliances).
[Note: pending clarification, we have not provided excerpts of Table C-9-G because, frankly, some of its data is confusing. - Ed.]
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
- [2] Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
- [3] Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
- [4] NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
- [6] NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
- [7] GAMA -
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
- [8] National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
- [9] Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
- [10] Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
See the complete table of the "Capacity of Double-Wall or Asbestos-Cement (Transite) Type B vents with Single Wall Connectors Serving a Single Appliance", Table C-9-A in Appendix C.
See the complete table of the "Capacity of Type B Double Wall Vents with Type B Double Wall Vent Connectors Serving a Single Appliance", Table C-9-B in Appendix C.
- New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
- [11] New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
- [12] "Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
- [13] Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
- "Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
- [14] "Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
- [15] "Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/chimneys.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
- [16] Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
- [17] US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Fireplace & Chimney Design, Repair Books - Fireplaces, Chimneys: design, repair
- Fireplace & Chimney Inspection Books - Inspecting and diagnosing chimney problems, fireplace problems, chimney & fireplace standards
- Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
- Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
- Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
- Fireplaces, a Practical Design Guide, Jane Gitlin
- Fireplaces, Friend or Foe, Robert D. Mayo
- NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
- Principles of Home Inspection: Chimneys & Wood Heating (Principles of Home Inspection), Carson Dunlop
- NFPA 211 - 3-1.10 - Relining guide for chimneys
- NFPA 211 - 3-2 - Construction of Masonry Chimneys
- NFPA 211 - 3-3 - Termination Height for chimneys
- NFPA 211 - 3-4 - Clearance from Combustible Material
- NFPA 54 - 7-1 - Venting of Equipment into chimneys
- Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
- American Gas Association - New Vent Sizing Tables
- Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
- National Chimney Sweep Guild - Yellow Pages of Suppliers
- ...
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