A.I.A. File No. 30-D-3

design ofgrease filter

equippedkitchen exhaust

systems

RPJtoU RESEARCH PRODUCTS CORPORATION

® Research Products Corporation 1967

.

Table of Contents

PAGE NO.

HOODS, WHY? 3

GREASE FILTERS, WHY? 3

TYPES OF HOODS —_ 3

Ventilator Hood 4

Canopy Hoods 4

Canopy Standard Hood . 4

Canopy Slot Hood = 5

DESIGNING THE KITCHEN EXHAUST SYSTEM 6

Step No. 1, Hood 6

Step No. 2 Air Volume _ 6

Step No. 3 Filters Required 6

Step No. 4 Exhaust Duct 7

Step No. 5 Resistance to Air Flow 8

MAKE-UP AIR 9

CODES 10

ACCESSORY ITEMS 10

SUMMARY 10

SAMPLE PROBLEM DRAWING 11

SAMPLE CALCULATION 12

CALCULATION SHEET .__ 13

2

Design of GreaseFilter EquippedKitchen ExhaustSystems

The need for a well designed grease filter equippedkitchen exhaust system has become widely recog-nized. Authoritative organizations, as well as localfire and health inspectors and industrial commissions,realize its importance. The properly designed ex-haust system encourages better \vorking conditionsand, therefore, improves employee efficiency.

Hoods, Why?The purpose of the hood is to capture, as nearly as

possible, all the heat, smoke, odors, grease, and greasevapors produced in the cooking process and to containthem until the fan can exhaust them.

Grease Filters, Why?Frequently, flash fires originating from cooking

operations spread from the stove to grease deposits inthe exhaust system. Non-filtered systems are prone tocollect accumulations of highly combustible grease de-posits throughout the entire duct system. Because ofthe chimney effect created in vertical duct work, avery intense rapidly spreading fire can engulf the en-tire system. A filtered system is protected from ex-tensive damage because grease filter deposits arelimited in quantity to that collected between cleanings(usually once a week) and the smaller amount ofgrease is confined to the grease filters. The build-upof extensive grease deposits in out-of-sight, inacces-sible locations is limited to the very small amount thatpasses through the filters (with efficient grease filters,usually less than 5%).

Grease filters protect exhaust equipment. Whenfilters are not used in the exhaust system, grease willcollect on the blower wheel and motor. This is detri-mental in many ways. Grease deposits on the wheelwill cause unbalance resulting in unnecessary bearingwear. Grease accumulations on the motor will causeoverheating which will create an additional fire haz-ard. The grease also has a tendency to deteriorate theinsulation on wires thus adding another fire hazard.

Grease filters simplify cleaning because grease de-posits are collected on the filter in an easily accessiblearea. Minimum cleaning problems promote regularcleaning, thus safety, sanitation, and health standardsare greatly improved.

Grease filters have established themselves as an ex-tremely important part of any kitchen exhaust system.In many areas, they are required by law. They shouldbe included in any newly designed hoods and incor-porated in remodeled hoods. The design and selec-tion of grease filters play an important role in the over-all effectiveness of the entire kitchen exhaust system.

Types of HoodsThere are two basic hood types:1.2.

Ventilator or back shelf hood. (Pi fa L ]Canopy type hoods.a. Canopy — island hood.b. Canopy — wall hood.c. Canopy — corner wall hood.d. Canopy — apron or wall protected.e. Canopy — slot type hood.

Ventilator or Back Shelf HoodThe ventilator or back shelf hood (Figure 1) is

designed to be as close as possible to the cookingsurface, usually 18 to 24 inches above it. Heat andfumes are caught close to the point of origin. Theentrainment velocity moves the air under the shelfaway from the cook. The design details of ventila-tors and auxiliary equipment are generally furnishedas a package by the manufacturer of this type equip-ment. Various patented features may be included.Usually the hood is pre-assembled, then installed ac-cording to manufacturers' recommendations. Thedesign of the filter and hood will not be covered inthis brochure because of this fact; however, the fan,motor and duct work are basically the same as willbe covered in detail later in the text.

The exhaust air volume through a ventilator hoodwill vary from approximately 300 to 350 cfm per linealfoot of hood length. If a hood of this type is beingconsidered, the manufacturer should be consulted(see Figure 1, Ventilator Type Hood).

Canopy HoodsThe more commonly used canopy hoods have sev-

eral variations. Figures 2a, b, c, & d show the fourbasic variations of this hood design.

Fig. 2a CANOPY-ISLAND type with 4 sides exposed.

Fig. 2b CANOPY-WALL type with 3 sides exposed.

Fig. 2c CANOPY-CORNER WALL type with 2 sidesexposed.

Fig. 2d CANOPY-APRON protected with only 1 sideexposed.

The canopy type hood, since it is by far the mostwidely field fabricated will be used as the hood inthe step-by-step design problem that we will develop.

0

Fig. 1

Fig. 2a

ISLAND CANOPY

-IfT

Fig. 2d

APRON CANOPY

Fig. 2bFig. 2c

CORNER CANOPY

WALL CANOPY

Fig. 2eFig. 2e CANOPY-SLOT type hood. An example

lay-up and filter placement for a typical hoodis shown.

The slot type hood is not primarily designed for thecommercial kitchen exhaust system; however, it isperiodically called for by the design engineer. Thishood is also sometimes called a double cavity hood orjust plain slotted hood.

There are potential problem areas when utilizinga hood of this design.

The heat generated in the cooking process is not jexhausted as rapidly as in the conventional design.

Filter placement and design and good fit are diffi-cult in a hood of this design.

The cleanability of the filters, as well as the clean-ability of the entire hood cavity becomes more diffi-cult with this design.

If the canopy-slot type hood is to be used, it hasits greatest value in the extremely large island type(4 sides exposed) hood design.

The greatest asset of this type hood is the removalof smoke and grease contaminants with the minimumexhaust requirement. However in .many applicationsmore ventilation air is required than exhausted, sothe prime reason for having this type hood is lost.

The hot contaminated air rises from the cookingsurface and is held in the hood cavity until such timeas it can be removed through the slot that goes com-pletely around the perimeter of the hood. Two im-portant design considerations are (1) have the hoodas low as possible over the cooking surface and (2)extend the hood out 1 foot minimum beyond the edgeof the cooking surface.

Typical hood construction would have a 2 to 4 inchslot around the entire perimeter of the hood. The airvelocity through this slot is normally between 350and 450 fpm.

The placement and choice of filters is importantsince the optimum air flow through grease filters isapproximately 350 fpm. This will make it necessaryto blank off several areas in the filter rack to increasethe speed of air through the remaining spaces thathave filters.

Lack of field information and design criteria forthis type hood limits its use.

SLOT

-^3"USO'3"SLOT - SO 'L4OG /v"/V 7Wf<y SLOT4OO FfMl • 400 CfMfVf&Y 4'Of SCOTso/4 s 12. ff SLOT je*A/2.s x 400 • sooo

. 400

Designing the Kitchen Exhaust System(See Sample Problem)

Following is an example of the recommendedstep-by-step procedure for the design of a grease filterequipped kitchen exhaust system. Critical specifica-tions to be determined are:

1. Dimensions of the hood.2. Volume of air to be exhausted.3. Number of filters required.4. Diameter of the duct from the hood to the

point of discharge.5. Resistance against which the blower must ex-

haust the calculated volume of air.6. Make-up air.7. Codes.

Step No. 1To Determine Dimensions of the Hood

The dimensions of the base of the hood are largerthan the cooking surface it covers to adequately re-move the contaminants generated in the cookingprocess. A general rule that has proved very satis-factory is summarized as follows: The length andwidth of the hood base should equal the overalldimension of the appliances it covers plus a 1 footminimum overhang on each side of the equipmentthat is not enclosed by an apron or an adjacent wall.The distance from the base of the hood to the cookingsurface will normally be 3 to 4 ft. since the kitchenemployees must work underneath the hood. Excessiveclearance between the cooking surface and hoodhampers the effectiveness of the exhaust system andshould be avoided. Four feet is maximum.

Step No. 2Volume of Air to be Exhausted

The volume of air to be exhausted is governed bystate or local codes. The velocities, as shown on thefollowing table, will insure efficient removal of the

o 'cooking contaminants.

TABLE 1Number ofExposed Sides4 canopy-island3 canopy-wall2 canopy-corner wall1 canopy-protected apron

(Note: Identification drawings of the 4 variations ofthe canopy hood can be seen on the calculation sheet.)

Air Velocity (FPM)Across Area of Hood

125100100100

The previous figures should be somewhat higherfor charcoal and charcoal type cooking. Some citycodes demand double exhaust volumes for these cook-ing areas.

Step No. 3Number of Filters Required

It is necessary to select the proper number of thecorrect size grease filters of a reputable make. Toomany filters increase cost and reduce the filter effi-ciency since the velocity through the filter will bereduced below the optimum rating. Too few filtersincrease the resistance to air flow and also increase thefilter cleaning frequency. Optimum operating con-ditions for most grease filters is at a face velocity of350 fpm.

The number of filters required in the hood can bedetermined by dividing the total volume of air to beexhausted by the cfm rating of the filters. The manu-facturer's optimum rating should be used (see TableII). The use of standard size filters is advisable froma cost, delivery, and replacement standpoint. Anyspace in the hood not filtered should be blanked offwith sheet metal. It is important to install filters atthe ends of the hood. The blanked-off space, if re-quired, should be divided equally between the filters.This will insure optimum performance and will equal-ize the air velocity over the entire length of the hoodopening.

TABLE IINominal Sizes Optimum Ratings (CFM)

20 x 25 100020 x 20 80016 x 25 80016 x 20 64015 x 20 60010 x 20 400

The hood itself must be deep enough to permit theinstallation of the grease filters at a minimum 45°angle from the horizontal. This "will eliminate greaseglobules dropping back onto the cooking surface.Most filters are designed so that the accumulatedgrease will run down the face of the filter and dropfrom the lowest edge into a drip tray. A design ofthis type also permits enough volume in the hood sothat unusually large "puffs" of steam and greasyvapors have a place to accumulate until the exhaustfan can remove them. This design also allows mixingof room air with the hot air over the cooking area.Proper design keeps the temperature at the filters less €

than 200 °F., and reduces the possibility of accumulat-ed grease run-off or vaporizing and passing throughthe filters. There isn't a grease filter made that willeffectively remove vapors. Assuming that the temper-ature at the filters is less than 200°, the grease depositwill be brownish and easily removed. Above 200°,the deposit tends to bake on the filter media, darken-ing in color, and is extremely difficult to remove.

Some codes suggest that the minimum height fromthe cooking surface to the lower edge of the greasefilter should not be less than:

a. No exposed flames — grills, French fryers, etc.— 2^ ft.

b. Exposed charcoal and charcoal type fires — 4M ft.c. Exposed fires other than b. — 8/2 ft.

Step No. 4Design of the Exhaust Duct

The duct leading from the kitchen exhaust hood tothe point where the exhaust air is discharged must becorrectly sized. The velocity of the exhaust air mustbe high enough to minimize condensation on the vari-ous parts of the duct system; however, avoid the useof excessively high air velocities because of the result-ing noise. Also, more power is required to drive theblower.

It is important to discharge the air at a loca-tion that will not cause discomfort to the people inthe vicinity or damage surrounding property. Thebends and elbows of the duct work should be kept ata minimum. When elbows are used, a radius of 2 to2)2 times the duct diameter is recommended. Thiswill minimize the resistance against which the blowermust remove the air.

The duct take-off at the top of the hood should betransitioned. This will reduce the entrance loss andresistance offered to air flow at the entrance point.If the hood length exceeds 10 ft, it is desirable tohave two discharge ducts from the top of the hoodjoin the main exhaust duct. These should also betransitioned where they join the hood. This insuresgood air distribution throughout the entire hood area.

Two thousand (2000) ft. per minute velocity shouldbe used to determine the duct diameter, unless other-wise specified. The area of the duct (sq. ft.) can becalculated by dividing the total exhaust CFM by 2000fpm. This duct area is converted to a diameter inTable III.

Table III can also be used to determine the branch ":duct size if more than one discharge duct is required.Divide the total volume of air to be exhausted by the Snumber of branches to determine the cfm per branch. \Then divide the cfm per branch by 2000 fpm to givethe sq. ft. area which can be converted to a ductdiameter.

TABLE III

Duct Area(Sq. Ft.)

.545

.7851.0691.3961.7672.1822.6403.1423.690

, 4.2764.9095.5806.3106.0807.8808.720

10.55012.550

Duct Diameter(Inches)

101214161820222426283032343638404448

Friction Loss/Ft. of Duct

(Inches W.G.)

.0058.0047.0039.0033.0029.0025.0023.0020.0018.0016.0015.0014.0013.0012.0012.0011.0010.0009

DUCT CONSTRUCTION

See National Fire Protection Association StandardNo. 96, Ventilation of Restaurant Cooking Equip-ment 1964 for more information.

Important considerations in duct construction are:1- A circular duct requires a smaller space. If rec-

tangular ducts are used, they should be as nearlysquare as possible.

2. The duot should be constructed of 18 gauge orheavier steel (see NFPA #96).

3. A minimum of 18" clearance should be providedfrom unprotected combustible construction. (SeeNFPA #96, Appendix B, for clearance from pro-tected construction.)

4. The joints in the exhaust duct must be made air-tight to prevent any leakage.

5. Exhaust ducts from kitchen hoods must be inde-pendent and not connected with any other ventil-iating system.

6. Access openings for inspection and cleaning pur-poses should be provided at least every 20 ft.in the system.

7. Vertical risers should be located outside thebuilding and adequately supported by the exteriorbuilding wall. When risers must be locatedwithin the building, they should be enclosed in ashaft constructed of 4" hollow tile or its equiva-lent. Access openings and a base residue trapshould be provided on all risers. Exhaust ductsshould not pass through fire wall.

Step No. 5Resistance Against Which the Blower Exhauststhe Calculated Volume of AirIt is essential that the blower selected meet the follow-ing two requirements:1. It must exhaust the calculated volume of air.2. It must exhaust this air against the maximum re-

sistance encountered in the entire kitchen exhaustsystem.

While the use of a propeller type fan may be tempt-ing, they normally do not work well against the resist-ance encountered in a commercial kitchen exhaustsystem. The use of a blower for best results is stronglyrecommended. To conserve the exhaust air, a 2 speedmotor is suggested. Low speed can be used duringthe "off," or low production time, and the high speedfor peak production loads.

Other factors that might influence the selection ofa blower are location, space limitations, permissiblenoise level, installation and operation costs; however,#1 and #2 are the primary requirements.

This resistance is usually assumed to be the total ofthe following four items:1. The resistance of the grease filter as based on the

manufacturer's rating. Rather than using theclean resistance, a value should be used whichrepresents the filter's resistance after it has accum-ulated a substantial quantity of grease. A valueof .2" water gauge is ample for most filters.

O O i-

2. "The entrance loss" resistance occurring wherethe exhaust duct attaches to the hood will beapproximately .1" water gauge when the exhaustduct velocity is approximately 2000 fpm. Theopening at the hood and discharge duct should betransitioned as shown by the hood sketches on thecalculation sheet.

3. The resistance from wind currents at the exhaustopening will vary anywhere from .1" to .5" watergauge depending upon the type and location ofthe outlet and on local wind conditions. .5 inchesis a maximum figure and should be used only ifthe exhaust is directly into the prevailing winds.Normally, something substantially less will beused. .2" water gauge is satisfactory in mostinstallations.

4. The resistance of the duct system is the total ofall the straight duct, plus the elbows and bends

expressed in equivalent length of straight duct.

The total of the two sums is then multiplied bythe friction loss per foot for the duct size and airvelocity involved. Table III can be used to deter-mine the friction loss per foot of duct. The equiv-alent length of straight duct for bends varies con-siderably depending upon the angle of the turnand the radius of the bend. A radius of 2 to 2&times the duct diameter is desirable and wouldrepresent what is considered long bends. If theradius of the bends is less than 2 times the ductdiameter, they are considered short bends. TableIV can be used to determine the equivalent lengthof straight duct represented by 90° and 45° longbends.

TABLE IVEquivalent Length of Long Bends

Type of Duct Diameter Duct DiameterBend Under 12" Over 12"90° 1 ft./in. of 1.25 ft./in. of

duct diameter duct diameter

S\W

45° % ft./in. ofduct diameter

% ft/in, ofduct diameter

As mentioned previously, the hood that exceeds 10ft. should have more than one duct take-off. Whentwo or more discharge ducts are used, there will bean entrance loss where the branch duct enters intothe main discharge duct. This must be included incalculating the system resistance. Table V givesresistance figures for air velocities of 2000 ft. perminute.

TABLE V30° angle of entrance = .05" water gauge45° angle of entrance = .07" water gauge60° angle of entrance = .12" water gauge

For uniform air movement over the entire length ofthe hood, the resistance in each branch should beequal.

For purpose of fan selection, the highest single re-sistance of any branch connection is added to theresistance of the system beyond the point of entry atthe main duct.

The total resistance against which the blower mustmove the calculated volume of air is then determinedby totaling the resistance values obtained as describedabove.

For more detailed information on duct sizing, en-trance loss, equivalent lengths of different type bendsand elbows, consult the ASHRAE Guide or NationalWarm Air Duct Calculation Manuals.

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mm.

Make-up AirMake-up air or replacement air must be introduced

into the establishment and be approximately equal tothe amount of air exhausted by the kitchen equipmentand any other exhaust fans in the building. If make-up air is not designed into the system, the buildingwill be under a negative pressure and this could causethe following serious problems:1. The exhaust fan could not exhaust the design

volume of air because it is not available.2. Negative pressure would cause improper venting

of water heaters, space heaters, or other individ-ually vented gas appliances in the building.

3. It would also cause a rush of unconditioned out-side air into the building whenever entrancedoors are opened.

The codes of most cities and states require ventila-tion to the dining area. This provides clean, freshair to maintain comfortable air temperatures andhumidities. Since most codes will specify a specificamount of ventilation air, this air can be exhaustedthrough the kitchen exhaust system after it movesfrom the dining area into the kitchen area. If theventilation air is less than the calculated exhaust re-quirement over the cooking area, and it normally is,the difference should be supplied directly into thekitchen through a make-up air system. Introducingoutside air by simply opening a kitchen windowshould be avoided since there is no control over whenand how much air will come in or actually even whenthe windows will be open. Cold, outside air duringthe winter months would be extremely uncomfortableand create serious drafts.

The recommended procedure is to supply outsideair through a designed make-up air system located toprevent drafts. The air should be tempered by sepa-rate control and filtered. The air velocity through themake-up air system should be low enough to eliminatethe possibility of drafts. It is important that the lo-cation of the air inlets is carefully considered to elim-inate any short circuiting.

A hypothetical restaurant layout as shown on Fig.3 will be a typical example. This is a one-storybuilding, 40 ft. wide by 100 ft. long with a 10 ft.ceiling. The dining area is 40 x 85 and the kitchenis 15 x 40.

The dining area of the restaurant, including thecocktail lounge, will seat 100 persons. Assuming thatthe local code requirement is 15 cfm of outside airper person, the heating and air conditioning system isdesigned to bring in 1500 cfm of outside air. Thisfresh air, along with the recirculated air, is condi-tioned year-round. It is generally considered gooddesign practice to have the air moved from thedining area into the kitchen.

Correct kitchen exhaust design procedure requiresthat we discharge 100 cfm per sq. ft. of hood base.

A 3& x 7 ft. wall type hood is required to cover the2& x 5 ft. cooking surface. This gives us a hood basearea of 24M sq. ft. 100 fpm x 243a sq. ft. gives anexhaust requirement of 2450 cfm.

It would be impossible to exhaust 2450 cfm. whenwe bring in only 1500 cfm; therefore, an additionalquantity must be introduced. The air should bebrought in the kitchen area with properly locatedoutlets.

It is desirable to have the kitchen under a veryslight negative pressure (.02" water gauge maximum) .This prevents any infiltration of cooking odors fromthe kitchen into the dining area. If the exhaust ex-ceeded the intake, it could create the problems aspointed out in the opening paragraph. Our hypo-thetical restaurant layout keeps the dining area underslight positive pressure and the kitchen area undera slight negative pressure.

3200 -SQ.fT.

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SAMPLE PROBLEM

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NOTE; tf 4 D&fW/M? OA/LY.

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SAMPLE CALCULATION

STEP NO. 1TO DETERMINE WIDTH & LENGTH OF HOOD1 - _J60_"; w - ^3Q_"W = w+(12"xY) .W = j2€L + ( 12 x — f- — ) = -z2_" = 5/a. ft.L = l+(12"xZJL = &+ (-UL*-2^)= -S4_- = _Z_ ft.

STEP NO. 2TO DETERMINE VOLUME OF AIR TO BE EX-HAUSTED

CFM = FPM (See Table 1) x L(f t ) x W(ft.)CFM = -&Q- x -3— x -ifc- = l&SD

TABLE 1Number of Air Velocity (FPM)Exposed Sides Across Area of Hood4 canopy — island 1253 canopy — wall 1002 canopy — corner wall 1001 canopy — protected apron 100

STEP NO. 3TO DETERMINE THE NUMBER OF FILTERSREQUIRED

Nc ff l t - CFM (see step No: 2)Filter rating (see Table 11)

isi,, ^ffilto 2450 CFM 3 filNa of filters - 800 CFM- fllters

(For a fraction of a filter, use next whole number)

- n0^ TABLE II7

fr« RATING OF RP GREASE FILTERS4 Norn. Sizes RP Stock No. Opt. Rating (CFM)^^0x25 931 1000

W 20x20 932 800/0<^l6x25 933 800*%, 16 x 20 934 640,9 15x20 935 600

10 x 20 936 400

STEP NO. 4TO DETERMINE DESIGN OF EXHAUSTDUCT.

^ t CFM (see Step No. 2)UC r a Duct Velocity (If not specified, use 2000 FPM)

n f A < , 245O CFM /22 „ ftDuct Area- 2000 FPM sq'Use Table III to convert to duct diameter.

/ 2.2 „„ fj- — /5"/p fjiipf Hiimeter

\

TABLE IIIFriction Loss/

Duct Area Duct Diameter Ft. of Duct(Sq. Ft.) (Inches) (Inches W.G.)

.545 10 .0058

.785 12 .00471.069 14 .00391.396 16 .00331.767 18 .00292.182. 20 .00252.640 22 .00233.142 24 .00203.690 26 .00184.276 28 .00164.909 30 .00155.580 32 .00146.310 34 .00137.080 36 .00127.880 38 .00128.720 40 .0011

10.550 44 .001012.550 48 .0009

If more than 1 duct take-off is required, see body ofbrochure.

STEP NO. 5TO DETERMINE RESISTANCE FOR BLOWER &MOTOR SIZING

1. Resistance of grease filters when loaded (use.2"w.g.) .2

2. "Entrance loss" of air from hood to duct (if notspecified use .1" w.g. ) -1

3. Resistance of exhaust duct (use Table III Step 4and Tables IV & V below for calculating. ) 44

TABLE IVEquivalent Length of Lang Bends

Type of Duct Diameter Duct DiameterBend Under 12" Over 12"

90° 1 ft./in. of 1.25 ft./in. ofduct diameter duct diameter

45° M ft./in. of % ft./in ofduct diameter duct diameter

TABLE V30° angle of entrance — .05" water gauge45° angle of entrance — .07" w.g.60° ansle of entrance 12" w ET 'o o

4. Resistance from wind current at exhaust opening(if not specified, use .2) -2

Total resistance of system -94Siw> Vilowpir «r motor for 2450 <~!FM

(Step 2) against total resistance -94 (Step S),

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2? Grease Filter Equipped Kitchen Exhaust System Calculation SheetRESEARCH PRODUCTS CORPORATION

Madison, Wisconsin 53701

DATE:

NAME:

The recommended minimum distance from cookingsurface to grease filter shall be not less than:

1. No exposed flame (grills, French fryers, etc.) —2% ft.

ADDRESS:

CITY: STATE:

2. Charcoal and charcoal type fires — 4/2 ft.

3. Exposed fires other than Item 2 — 8/2 ft.

1 —length of cooking surface.w — width of cooking surface.L — Length of hood.W — Width of hood.D — Diameter of exhaust duct.Y — Number exposed sides in hood width.Z — Number exposed sides in hood length.

ISLAND CANOPY WALL CANOPY

CORNER WALL CANOPY PROTECTED APRON CANOPY

v=/z=o

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CALCULATION SHEET

STEP NO. 1TO DETERMINE WIDTH & LENGTH OF HOOD

1 "• w "W = w+ (12"xY)W i n ° ic } " ftL= 1 + (12"xZ)T 1 ( Y > " ftj_i — T ( x ; — - — - - • rt.

STEP NO. 2TO DETERMINE VOLUME OF AIR TO BE EX-HAUSTED

CFM = FPM (See Table 1) x L(ft . ) x W(ft .)/"•irXyf „ v

TABLE 1Number of Air Velocity (FPM)Exposed Sides Across Area of Hood4 canopy — island 1253 canopy — wall 1002 canopy — corner wall 1001 canopy — protected apron 100

STEP NO. 3TO DETERMINE THE NUMBER OF FILTERSREQUIRED

Filter rating (see Table II)

( For a fraction of a filter, use next whole number )

TABLE IIRATING OF RP GREASE FILTERS

Nom. Sizes RP Stock No. Opt. Rating (CFM)20 x 25 931 100020 x 20 932 80016 x 25 933 80016 x 20 934 64015 x 20 935 60010 x 20 936 400

STEP NO. 4TO DETERMINE DESIGN OF EXHAUSTDUCT.

CFM (see Step No. 2)Duct Velocity (If not specified, use 2000 FPM)

r> f \rr CFM r.Duct Area— FPM

Use Table III to convert to duct diameter.

<*q fa — duct diameter

TABLE 111Friction Loss/

Duct Area Duct Diameter Ft. of Duct(Sq. Ft.) (Inches) (Inches W.G.)

.545 10 .0058

.785 12 .00471.069 14 .00391.396 16 .00331.767 18 .00292.182 20 .00252.640 22 .00233.142 24 .00203.690 26 .00184.276 28 .00164.909 30 .00155.580 32 .00146.310 34 .00137,080 36 .00127.880 38 .00128.720 40 .0011

10.550 44 .001012.550 48 .0009

If more than 1 duct take-off is required, see body ofbrochure.

STEP NO. 5TO DETERMINE RESISTANCE FOR BLOWER &MOTOR SIZING

1. Resistance of grease filters when loaded (use.2" w.g.)

2. "Entrance loss" of air from hood to duct (if notspecified use .1" w.g. )

3. Resistance of exhaust duct (use Table III Step 4and Tables IV & V below for calculating. )

TABLE IVEquivalent Length of Long Bends

Type of Duct Diameter Duct DiameterBend Under 12" Over 12"

90° 1 ft./in. of 1.25 ft./in. ofduct diameter duct diameter

45° M ft/in, of % ft./in ofduct diameter duct diameter

TABLE V30° angle of entrance — .05" water gauge45° angle of entrance — .07" w.g.60° angle of entrance — .12" w.g.

4. Resistance from wind current at exhaust opening(if not specified, use .2)

Total resistance nf system

Si?* blower & motor for CFM

(Step 2) against total resistance (Step 5),

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