Category PLUMBER’S AND. PIPE FITTER’S. CALCULATIONS MANUAL

Choosing materials for a venting system is not usually much problem. Most jobs use Schedule-40 plastic pipe for vent pipes. There are, however, other options for vent materials. And, not all codes allow the same types of vent ma­terials. You will also notice from the following tables of approved materials that there can be a difference in approved materials for vents that are installed underground, compared to those installed above ground. We will close out this chapter with tables that indicate what types of materials are allowed within major plumbing codes.

FIGURE 5.49 ■ Materials approved for above-ground vents in Zone Two. (Courtesy of McGraw-Hill)

FIGURE 5.51 ■ Materials approved for underground vents in Zone One. (Courtesy of McGraw-Hill)

FIGURE 5.50 ■ Materials approved for above-ground vents in Zone Three. (Courtesy of McGraw-Hill)

FIGURE 5.52 ■ Materials approved for underground vents in Zone Two. (Courtesy of McGraw-Hill)

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Riser diagrams are often required by code officers prior to any plumbing be­ing installed. Supplying a detailed riser diagram (Fig. 5.44 and Fig. 5.45) is usu­ally a standard part of a permit applica­tion. You can also use riser diagrams to help you when sizing a vent system. If

you draw a riser for the job you are working with, the diagram will make it easier for you to label the fixture-unit loads and the sizes of the vents re­quired. Another good use of a riser diagram is to minimize wasted piping. If you draw your piping path on paper, you can spot situations where an alter­native plan might be used to minimize the cost of labor and materials (Fig. 5.46 and Fig. 5.47).

Supporting a vent system is another element of a system design. The spac­ing allowed for support varies from code to code and with the type of pipe being used in the vent system. The tables below will show you some examples of recommended minimums for support spacing.

FIGURE 5.38 ■ Horizontal pipe-support intervals in Zone Two. [Courtesy of McGraw-Hill)

FIGURE 5.39 ■ Vertical pipe-support intervals in Zone One. [Courtesy of McGraw-Hill)

Type of vent pipe Maximum distance between supports (ft)

ABS Cast iron Galvanized PVC Copper (2 in and larger) Copper (ІУ2 in and smaller)

FIGURE 5.41 ■ Vertical pipe-support intervals in Zone Two. (Courtesy of McGraw-Hill)

FIGURE 5.42 ■ Horizontal pipe-support intervals in Zone Three. (Courtesy of McGraw-Hill)

Sump vents, the ones used to vent a sump system, are calculated on a basis of a pump’s discharge capacity. Tables are often provided for this type of sizing. See Figure 5.37 for an example of such a table. Using a table like this one, you can quickly and easily size a vent for a sump. As long as you know the discharge rate of the pump being used in the sump, the rest of the work is simple.

Wet venting is popular, but a little different when it comes to sizing the vents. Tables can still be used for this type of sizing. Look at Figure 5.34 for an ex­ample of a table that might be used to size a wet stack vent. Another type of table that you might encounter is shown in Figure 5.35. This table is intended for use in sizing a vent stack for wet venting.

Keep in mind that not all plumbing codes are the same, and they may present their information differently. It is also important to remember that re­quirements may be different.

FIGURE 5.34 ■ Table for sizing a wet stack vent in Zone Two. (Courtesy of McGraw-Hill)

FIGURE 5.35 ■ Table for sizing a vent stack for wet venting in Zone Two. (Courtesy of McGraw-Hill)

Stack vents, vent stacks, and relief vents require more information for sizing. Specifically, you must know the fixture-unit load on a drain before you can determine vent sizing and developed lengths. Once you have calculated the fixture units, a sizing table can be used to give you your sizing information. The table shown in Figure 5.31 is the type of table that would be used to de­fine the requirements of stack vents, vent stacks, and relief vents. Like the other tables, this one is self-explanatory. To prove this, size the diameter and maximum length of a vent stack that will serve 20 fixture units with a drain di­ameter of two inches. Assume that you want your vent pipe to have a diame­ter of one and a half inches. The answer is that your vent size is okay, as long as you don’t extend it more than 50 feet. If you need more distance, increase the size of the vent to a 2-inch diameter and feel free to run the vent up to 150 feet. The table is easy to use, but you must be able to calculate the load of fixture units. How will you do that? I’ll show you.

Most codebooks will provide you with some form or a chart or table that identifies fixture-units for drainage piping. A table like the one in Figure 5.32 is quite helpful. By looking at such a table, you can quickly determine the load, in terms of fixture units, that an individual fixture puts on a drain. For example, a bidet carries a fixture-unit rat­ing of 2. A drinking fountain is rated for one half of a fixture unit. A residential wa­ter closet is worth 4 fixture units. By using this type of table to assign fixture-unit rat­ings to all fixtures being served by a drain, you can then arrive at a number to use with the vent-sizing table. For fixtures that are not listed, you can use a generic table, like the one in Figure 5.33, to assign ratings for fixture units.

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FIGURE 5.30 ■ Individual and branch vent sizing table for horizontal soil and waste branches. [Courtesy of Standard Plumbing Code)

FIGURE 5.31 ■ Maximum length of stack vents, vent stacks, and relief vents. (Courtesy of Standard Plumbing Code)

FIGURE 5.32 ■ Fixture units per fixture or group. (Courtesy of Standard Plumbing Code)

Let’s do a sizing exercise to illustrate how the tables from a codebook might be used to determine the size of piping needed for various vents. When you set up a vent sys­tem, you must know how far a vent is al­lowed to be from the trap it is serving. If you look at Figure 5.27, you will see the re­quirements for one of the major plumbing codes. The table is easy enough to understand. If you have a fixture drain that has a diameter of 1.5 inches and a trap size of 1.5 inches, with a grade of a quarter of an inch per foot, the trap may be as much as five feet from the vent. With this particular code, the dis­tance would remain the same, even if the trap size was only one and a quarter inches in diameter, so long as the drain remains as a 1.5 inch diameter.

FIGURE 5.27 ■ Distance of fixture trap from vent. (Courtesy of Standard Plumbing Code)

If the size of the fixture drain was three inches in diameter, with a 3-inch trap, and one-eighth of an inch of fall per foot, the vent could be up to 10 feet from the trap. Obviously, this type of table is easy to understand and to work with.

Vent sizing is based on developed length. This is the measured distance of all pipe used in the system. Measurements are taken on a center-to-center basis. You can see in Figure 5.28 how the measurements are assessed. Once you know the developed length of a vent, you can use a sizing chart to de­termine the minimum diameter of the vent pipe. The sizing of a vent or vent system is not difficult. Let me show you how it’s done.

Look at Figure 5.29. This is a chart designed for sizing individual and branch vents serving horizontal soil and waste branches. As you look at the table, you will see two types of abbreviations. The abbreviation shown as NP means "Not Permitted". When you see the abbreviation of UL, it means "Un­limited". Aside from these two clarifications, the table pretty much speaks for itself. Try to find the answer to the question I’m about to give you. Assume that you have a drain that has a 2-inch diameter. The amount of fall on the pipe is set at one quarter of an inch per foot. You want to run a vent with a di­ameter of 1.5 inches. How far can you run the vent in that size? The answer is that there is no limit to the length of the vent run. But, suppose you wanted the vent diameter to be 1.25 inch, how far could it go? A vent of this size

FIGURE 5.28 ■ Distance of fixture trap from vent. (Courtesy of Standard Plumbing Code)

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Diameter of horizontal drainage piping (inches)1 Slope of horizontal drainage branch (inches per foot) Maximum developed length (feet): measured from the connection to the most remote fixture served to either the outside termination or the connection to either the stack vent or vent stack diameter of vent (in) ІУ4 ІУ2 2 2У2 3 4 5 6 8 10 IV* V4 UL3 У2 UL l‘/2 ‘/4 UL UL Vi UL UL 2 Vi 874 UL UL V’2 437 UL UL 2 Vi ‘Л 286 756 UL UL Vi 143 378 UL UL 3 V. в NP 606 UL UL UL ‘/4 NP 303 UL UL UL ‘/2 NP 152 704 UL UL 4 Уя NP NP 666 UL UL UL ‘/4 NP NP 333 UL UL UL */2 NP NP 166 548 UL UL 5 ‘/я NP NP 218 716 UL UL UL ‘/4 NP NP 109 358 948 UL UL ‘/2 NP NP 54 179 474 UL UL

FIGURE 5.29 ■ Individual and branch vent sizing table for horizontal soil and waste branches. [Courtesy of Standard Plumbing Code)

could run for a developed length of 874 feet, which is far more than you would be likely to run it.

Now assume that you have a 3-inch drain and you want to run a vent that has a diameter of 1.25 inches. How far can it go? It can’t be used. This is in­dicated by the NP symbol. The reason for this is that the vent must be at least half the size, in diameter, of what the drain being served is. There are excep­tions to this rule as the size of drains become larger. This means that the smallest vent diameter allowed for a 3-inch drain is a 1.5-inch vent. A vent of this size could run for 606 feet. When you deal with large-diameter drains, you have to move up to larger vent sizes to achieve unlimited runs of distance. This can be seen in Figure 5.30. You would use the table in Figure 5.30 in the same way that we used the previous sizing table.

Sizing tables are often used when sizing vent pipes (Fig. 5.21). There can be many different types of tables to use during a sizing procedure. For example,

FIGURE 5.21 ■ Vent sizing table for Zone Three (for use with individual, branch, and circuit vents for horizontal drain pipes). (Courtesy of McGraw-Hill)

you might use one table to size a vent stack (Fig. 5.22) and another table to size a wet stack vent (Fig. 5.23). Some codes might use one table for both types of vents (Fig. 5.24). Then you might have a different table to use when sizing branch vents or circuit vents (Fig. 5.25). Battery vents may require a dif­ferent table (Fig. 5.26). Once you have a sizing table to work with, sizing a vent system is not a complicated process.

FIGURE 5.22 ■ Sizing a vent stack for wet-venting in Zone Two. (Courtesy of McGraw-Hill)

FIGURE 5.23 ■ Sizing a wet stack vent in Zone Two. (Courtesy of McGraw-Hill)

FIGURE 5.24 ■ Vent sizing for Zone Three (for use with vent stacks and stack vents). (Courtesy of McGraw-Hill)

FIGURE 5.25 ■ Vent sizing for Zone Three (for use with individual, branch, and circuit vents for horizontal drain pipes. (Courtesy of McGraw-Hill)

The distance from a trap to a vent is determined by local plumbing code re­quirements. Allowable distances are usually given either in text or in tables within a codebook. There can be a sig­nificant difference from one code to the other. To illustrate this, I’d like you to refer to Figures 5.18, 5.19, and 5.20. The tables you see in these illustrations represent differences between three major plumbing codes. You should no­tice that the distances from traps to vents is the same for two codes and dif­ferent for one code. You must refer to the plumbing code that is being en­forced in your area for specific sizing requirements. The information pro­vided here is representative of the types of charts, tables, and information you will likely work with, but it is not necessarily the code that you will be

FIGURE 5.18 ■ Trap-to-vent distances in Zone One. (Courtesy of McGraw-Hill)

working with. Our intent here is to learn how to size systems, so consider the information here as a learning tool, rather than a code ruling.

Types of vents are numerous. Do you know what an island vent is? How much do you know about relief vents? Depending upon your level of knowledge in the plumbing trade, you might be aware of all types of vents, but not all read­ers are. Before we jump into sizing examples, I’d like to make sure that all of my readers are aware of the various types of vents. With this in mind, I will provide a number of vent drawings for readers to devour. So, let’s get on with the visual examples of various vent types.

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vent

Оси It Vert

Drain*

Vert

Branch Vent

<=Vent

Vent

Drain

Drain

L*Qend

Vent

Drain

Legend

Drain

Vent

Vent Stack

11/2* Trap

Trap Ann

Drainage Branch

vent Stack

Drainage Branch

Drainage Branch

Drainage Branch

Soil Stack

Building Drain

► sensible shortcut