SIZING HANDBOOK SIZING HANDBOOK & APPLICATION GUIDE Chimney & Gas Vent For Capacities to 100 Million B.T.U. The primary aim of this Sizing Handbook is to provide more detailed guidance on appliance venting than can be found in the codes or in appliance manufacturers' instructions.
Sizing Handbook & APPLICATION GUIDE Gas Vent and chimney products for capacities to 100 million BTU per hour 2001 Revision Including Tables For Fan-Assisted Combustion Appliances WARNING Failure to follow the installation instructions could cause FIRE, CARBON MONOXIDE POISONING, OR DEATH. If you are unsure of installation requirements, call the phone number listed on the instructions or Sizing Handbook.
CONTENTS FOREWORD Application Maximum and Minimum Capacities Selkirk Product Information SECTION 1 Individual Vent Table 1-1 1-2 1-3 1-4 1-5 1-6 Definitions Procedure for Using the Individual Vent Table Example 1, Vent for a FAN-Assisted Appliance Vent Size Reductions Vertical Vents Additional Important Information SECTION 2 Combined Vent Tables 2-1 2-2 2-3 2-4 2-5 2-6 Definitions Headings in the Combined Vent Tables General Procedure Procedure to Find Each Connector Size Procedure to Find Common Ven
CONTENTS SECTION 7 SECTION 11 7-1 7-2 7-3 7-4 7-5 7-6 7-7 7-8 7-9 7-10 7-11 7-12 7-13 11-1 11-2 11-3 11-4 11-5 Multi-Story Venting General Indirect Appliances Only Excluded Appliances: Direct Types Fundamental Design Principles Separation from Occupied Spaces Air Supply Functions and Sources Air Supply Methods and Details Common Vent Location Applying Combined Vent Tables to Multi-Story Systems Example of Multi-Story Vent Design Some Important Precautions Number of Connections to Multi-Story Vents Para
FIGURES FIGURE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 4 SEC. REF. Individual Vent - Lateral and Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 Example of Individual Vent Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FOREWARD APPLICATION This updated version of the Selkirk Sizing Handbook features tables of maximum input capacity rating for fan-assisted combustion Category I appliances, as well as those for draft hood appliances. Both individual and combined vents are included. In addition, the tables include minimum capacity values for fan-assisted combustion Category I appliances.
The first seven sections of this Handbook are applicable to gas-burning Category I equipment. Sections 1 and 2 provide tabulation of maximum inputs for both draft hood and fan-assisted equipment, as well as minimum inputs applicable only to fan-assisted equipment. Sizes from 3" to 24" diameter are covered with allowances for height and lateral length, as well as connector rise and operating combinations for combined vents.
PRODUCT INFORMATION These tables for individual and combined vents apply to size selection and system design for the complete spectrum of Selkirk vent and chimney products, with exceptions as noted in the Application Table below.
INDIVIDUAL VENTS - TABLE I Capacity of Selkirk Gas Vents when connected directly to one appliance. (Not applicable to combined vents.
INDIVIDUAL VENTS - TABLE I Capacity of Selkirk Gas Vents when connected directly to one appliance. (Not applicable to combined vents.
INDIVIDUAL VENTS - TABLE II Capacity of Selkirk Gas Vents with single wall metal connectors.* (Not applicable to combined vents.
1-4 VENT SIZE REDUCTIONS If the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the smaller size may be used provided: A. The total vent height "H" is at least 10'. B. Vents or connectors for appliance draft hood outlets or flue collars 12" in diameter or smaller are not reduced more than one size (e.g., 12" to 10" is a one-size reduction). C.
The "Common Vent" is that portion of the system serving two or more connected appliances. If connectors are joined before reaching the vertical vent, the run between the last entering connector and the vertical portion is also treated as part of the common vent. In Figure 3C, the vertical common vent is cross-hatched beginning at the interconnection tee.
COMBINED VENTS - TABLE III Capacity of Selkirk gas vents with Selkirk connector serving two or more appliances.
COMBINED VENTS - TABLE III Capacity of Selkirk gas vents with Selkirk connector serving two or more appliances.
COMBINED VENTS - TABLE IV Capacity of Selkirk gas vents with single wall metal connector* serving two or more appliances.
B. For the 105,000 BTU per hour furnace, enter the vent connector table at the same least total height (15') at a connector rise of 3'. Read across to 163,000 under the FAN MAX column. The MIN is 51,000. Therefore, 5" is the correct connector size. See Figure 3B. Specific types of appliances and/or equipment to which these tables apply include: C. For the common vent, the sum of the two ratings is 140,000 BTU per hour. Enter the common vent table at 15' least total height.
3-4 PROHIBITED APPLICATIONS OF TABLES The tables do not apply directly to: A. Wall furnaces (recessed heaters) which require Type BW vents. (See 4-1 A) B. Decorative gas appliances (gas fireplaces or logs) which generally require a specific vent size and are best individually vented. (See 4-1 D) C. Category II, III, or IV gas appliances, except that a Category III appliance may also be vented in accordance with Category I conditions.
There are several existing restrictions on single wall metal connectors in venting codes. These recognize that cold environments can lead to material or venting failure. Single wall metal connectors are prohibited in attics and cold areas by provisions in the National Fuel Gas Code as follows: "7.10.2 Materials: (b).
Rule 11 (14" and larger - or near walls) For installations other than covered by the table above, or closer than 8' from a wall or similar obstruction, the top should be located such that the lowest discharge opening is at least 2' higher than any portion of a building within 10'. Vent tops 14" size and larger must comply with Rule 11 regardless of pitch. 3-12 USE OF THE CHIMNEY FOR GAS VENTING The individual and combined gas vent tables apply to the Chimney only for draft hood (NAT) appliances.
SECTION 4 INDIVIDUAL VENTING length of lateral, the following maximum lengths for all Selkirk Type B vents are obtained from the individual vent table: (Table 4-1 APPLIANCE TYPES, SPECIAL CONSIDERATIONS A. ROOM HEATERS, FLOOR FURNACES, WALL FURNACES: If the appliance has a draft hood, assume an adjusted input 40 percent greater than name plate value and design vent for this increased input. Example: The vent for a 50,000 BTU per hour room heater will be 10' high with a 2' lateral. Adjusted input is 1.
4-4 COMPENSATING FOR EXTRA ELBOWS Capacities shown for individual vents with laterals make allowance for two 90 degree turns anywhere in the system. Fittings for these turns may be: A. Two 90 degree elbows B. One 90 degree elbow and one tee C. Four 45 degree elbows D. Two 45 degree elbows and one tee When more than two 90 degree turns are needed, a reduction in maximum (MAX) capacity must be made for each added turn. (Minimum capacity is not affect.
The connector tables for combined vents show MIN and MAX capacities only for FAN appliances because it has been found that no minimums are needed for NAT appliances with Type B gas vent connectors.
5-6 CONNECTOR TURN LIMITS: ELBOWS AND TEES To obtain full capacity, connectors for a combined vent should be limited to two 90 degree turns; either two elbows or an elbow and a tee as previously shown in Figure 3. If more turns are needed, there are three choices: A. Use the next size larger connector (this may increase minimum capacity) B. Use 1' more rise, if this is possible C. Reduce maximum connector capacity by 5 percent for each additional elbow up to and including 45 degrees.
5-10 WHEN IN DOUBT USE LARGER CONNECTOR Especially for combined vents, the maximum input for a connector may not allow it to be the same size as the draft hood or flue collar and a size increase may be needed. Also, if there is any uncertainty that connector rise may be insufficient, use the next larger size and increase the size directly at the draft hood outlet. This simple size increase precaution will help avert draft hood spillage or positive pressure problems with a fan-assisted appliance.
6-3 COMMON VENT INTERCONNECTION FITTINGS Any tee used to join two connectors must be the same size as the common vent. The size of common vent called for by any of the three appliance combinations (FAN+FAN, FAN+NAT, NAT+NAT) determines the size of the tee. Using too small a tee will restrict flow when both appliances are operating. Correct choice of tee size is shown in Figure 16. This same rule applies to tee fittings used in manifolds, as will be discussed in Section 6-6.
6-9 CONNECTORS TO A MANIFOLD All connectors to a manifold must have the required minimum rise. If a small connector enters the lower end of a large tee, as in Figure 8, the rise should be measured from appliance outlet up to the level of the size increase. This rule of adequate rise is extremely important if more than two appliances are manifolded. Many codes required that lateral parts of a venting system be sloped upward 1/4" per foot.
6-13 SINGLE APPLIANCES WITH TWO OR MORE DRAFT HOODS OR FLUE OUTLETS 7-2 INDIRECT APPLIANCES ONLY Instructions for manifolding appliances having two or more outlets should be furnished by the appliance manufacturer. If not, the area of the manifold and its outlet connector should equal the sum of the outlet areas. If it is possible to shut off one or more of the side-by-side sections of such an appliance, all connectors into the manifold should conform to the connector rise provisions in the tables.
The recommendations for multi-story venting of gas appliances are theoretically sound and have proven themselves in many years of successful operation. The method of design of vents serving indirect appliances is simply an extension of previously developed combined venting principles and now applies to both draft hood and fan-assisted combustion appliances. The capability of multi-story venting combining these two types of appliances has been verified by laboratory tests.
To illustrate the ready applicability of the outside wall method, Figure 21 shows a small portion of a typical highrise venting system. A closed solid door or panel separates the appliance room from the inside of the building and both the cold air return and outlet plenum are attached to the furnace. Additionally, a change to horizontal ducts would permit the appliance room to be more centrally located.
7-11 SOME IMPORTANT PRECAUTIONS The connector for the single appliance at the lowest level is sized as an individual vent, terminating at the first tee or interconnection. For two appliances at the first and succeeding levels, as in Figure 21, both the connector and common vent tables are used starting at the lowest level and a total height up to the next tee or interconnection. A. Offsets in the common vent are limited to a single offset and can not exceed 45 degrees from vertical.
7-12 NUMBER OF CONNECTIONS TO MULTISTORY VENTS 7-13 PARALLEL SYSTEMS Using the Combined Vent Tables, the connector rise of the entering connector must be 1' greater than shown wherever the common vent size becomes more than 7 times the area of that connector. This permits the first several appliances at lower levels of the multi-story system to use tabulated connector rises.
REQUIRED FREE AREA FOR EACH OPENING OR DUCT, SQUARE INCHES BASED ON TOTAL INPUT* APPLIANCE TYPES IN ROOM Air Supply Draft Hood Combination Method (NAT) (FAN + NAT) A. All Air From sq. in. = Total Input Total Input Inside Building 1000 1000 B. All Air From sq. in. = Total Input Total Input Outdoors Through 4000 4000 wall Openings B. All Air From sq. in. = Total Input Total Input Outdoors Through 2000 2000 Ducts C. All Air From sq. in. = Total Input Total Input Ventilated Attic 4000 4000 D.
There are three possible locations for a draft blower or fan relative to the vent system: A. Connector or breeching inlet (same as equipment outlet). With a blower at this location, producing greater than atmospheric static pressure in the vent, all parts of the system can be considered under forced draft. This location is shown in Figure 26. B. Between the chimney connector and the vertical vent.
There is an added cost of electrical power, plus the draft equipment itself, and of controls to prove vent or chimney flow before burner ignition is permitted. 9-5 PRODUCT APPLICATIONS WITH MECHANICAL DRAFT For those Models RV, QC, DF, and Chimney products in the table below, the operating pressure requirement of neutral or negative requires that the draft inducer be placed either at the vent outlet or just ahead of the final single chimney length.
10-2 COMBINED GAS VENT GRAPH For combined gas vents serving appliances with draft hoods, Figure 30 indicates the size of the common vents only, or the size of a manifold for a given input and vent height. The capacities are thus conservative for vertical common vents serving just two appliances if there is no manifold or offset. In the 14" to 24" size range, the tables are to be preferred, however, Figure 30 is useful for heights greater than 100'.
10-3 CHIMNEYS FOR EQUIPMENT NEEDING DRAFT Many types of fuel-burning equipment require negative (below atmospheric) static draft at their outlets. This draft may be needed to assure adequate combustion air, to overcome variations in flow resistance through a fuel bed, or to prevent escape of combustion products from the combustion system. Studies of vents and chimneys larger than 10" diameter have shown that the effect of heat loss on capacity or draft drops appreciably up to 18" size.
10-5 CHIMNEYS OPERATING AT FORCED DRAFT 10-6 GENERAL FACTORS FOR CHIMNEY SIZING GRAPHS Many boilers and other types of fuel-burning equipment have sufficient blower power to develop positive outlet flue gas pressures. A common operating condition for their chimneys is at 0.50" water column greater than atmospheric pressure. With this much pressure added to theoretical draft, chimney size may be smaller than for neutral or negative draft systems.
The sizes and draft capability of systems using natural gas and propane have been compared with results from the Battelle computer program VENT II V 4.1. The comparison indicates that capacities given for those gases are adequate. Specifically, when Model PS resistance coefficients are used, VENT II V 4.1 shows that the chimney will produce negative, neutral, or positive pressure draft using the same operating parameters as were used for three graphs.
SECTION 11 GENERAL DESIGN METHODS For chimney systems of any complexity or differing from the specific configuration shown in Section 10, the general chimney design chart, Figure 34, can be used. This chart, technically a "Cascade Chart," is based on equations first published by ASHRAE in 1971. The equations and resulting design method are explained in the ASHRAE Handbook Equipment Volume, Chimney Chapter, and are given here in the sections to follow. 11-1 THE CHIMNEY DESIGN EQUATION (di2) I = 4.
11-3 DESIGN CHART RECOMMENDED FACTORS THEORETICAL DRAFT AT SEA LEVEL, Dt The tables to follow are for guidance in selecting reference points and lines on the design chart, or for solution of the design equation. (Relative to 60 degree F.
41 FIG.
G. Turn left again, horizontally, to temperature rise line in "C" grid. H. At temperature rise in "C," go vertically to the ∆p value as previously calculated in "D" grid. I. From ∆p, go horizontally to right to or between curved lines of input as appropriate in "E" grid. A. Enter grid A at 5.3% CO2 line, go to natural gas line, then vertically to 300 degree rise. B. Go to transfer line in grid B then to assumed k=7.5. At this point, follow dashed line for first trial.
43 FIG.
SECTION 12 CHECKING VENT SYSTEM OPERATION The major purpose of this Handbook is to provide dimensional and capacity information for venting systems to assure prior to installation that there will be adequate vent capacity and trouble-free operation. Many vents in the field, however, may deviate from these recommendations yet not pose any problems. Just because dimensions may differ is no automatic indication of a real or potential malfunction.
12-3 COLD BACKDRAFT If a draft hood appliance is not operating and cold air is coming out the relief opening, this is actually not a venting malfunction. For this to occur there must be an indoor outdoor temperature difference which causes cold air to be drawn down the vent, such as might occur if the vertical vent piping is entirely outdoors. This flow reversal also can be caused by fan or fireplace operation. See Section 3-13 for more discussion of this problem.
12-8 SUMMARY THE TROUBLE SHOOTING The following table indicates by X marks which problem may be expected in the many possible combinations of appliance and vents. The analysis is very brief for Categories II, III, and IV because these appliances are not likely to be used with Type B gas vent, nor are they permitted to be combined with draft hood appliances.
Canada Only CHIMNEY SIZING CHART FOR FIREPLACES Example: Fireplace Opening 42” W by 30” H Chimney Height 12’ Use 14” Diameter E AC 400 300 250 200 150 125 80 100 60 50 40 20 15 30 10 8 25 20 48 15 12 42 10 L EP R FI 60 36 8 30 6 5 4 24 3 Note: Chimney offsets are limited to 30° from vertical and require no additional considerations. 18 2 24 30 36 ALWAYS FOLLOW MANUFACTURER'S INSTALLATION INSTRUCTIONS. 48 60 72 84 FIREPLACE OPENING WIDTH, in.
SECTION 14 RELINING MASONRY CHIMNEYS 14-1 OPTIONS FOR RELINING When an existing masonry chimney is inspected and found to require modification in order to make it suitable for use with gas burning appliances, a variety of options are available.
From Appliance to Rooftop THE COOLEST UNDER THE HOTTEST CONDITIONS When independently tested at 2100° F in accordance with the UL 103HT chimney test protocol, "The Selkirk Sure-Temp Chimney exhibited the coolest (outer skin) temperatures..." Not surprising! Our unique insulation is designed and is thoroughly tested to meet our own strict internal standards before being pressure packed into each chimney section, ensuring a 100% fill.
