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Quiz: Fan Selection and Writing the Specification

Test your understanding of application requirements, the selection decisions, sound and dimension checks, and writing and reviewing a fan specification.

1. What does a fan efficiency grade (FEG) under AMCA Standard 205 rate?

  1. The fan's efficiency at the actual duty point, including the motor and drive
  2. The efficiency class of the motor that drives the fan
  3. The fan's peak total efficiency, adjusted for impeller diameter, for the fan alone
  4. The ratio of a reference fan's electrical input power to the actual fan's input power
Show Answer

The correct answer is C. An FEG classifies a fan's peak total efficiency, adjusted for impeller diameter, into bands such as FEG 67, 71, 75, 80 and 85. It rates the fan alone and says nothing about where on the curve the fan will run. Options A and D describe the fan energy index (FEI, AMCA Standard 208), which rates efficiency at the duty point and includes motor and drive losses. Motor efficiency (B) is a separate requirement.

Concept Tested: Fan Efficiency Grade

See: Efficiency Requirements

2. Why should you ask a customer for the range of airstream temperatures rather than a single value?

  1. Because the average temperature sets both the construction package and the motor size
  2. Because the hottest temperature sets the construction package, while the coldest sets the motor
  3. Because only the maximum temperature affects the selection, and the range confirms it
  4. Because the coldest temperature sets the construction class, while the hottest sets the motor
Show Answer

The correct answer is B. Temperature sets air density, which changes the pressure and power the fan needs. The hottest temperature decides the construction package, such as high temperature bearings, shaft seal and shaft cooler. The coldest temperature gives the densest air, so it decides the motor through the cold-start load. Option D reverses the two roles, and an average (A) hides both extremes. Missing requirements like this, not calculation errors, cause most bad selections.

Concept Tested: Airstream Conditions

See: Airstream Conditions

3. A fan at sea level must deliver its airflow against 6.0 in. wg static pressure with 400°F gas. Using d = (Pb ÷ 29.92) × 530 ÷ (T + 460), at what static pressure should you read the standard-air catalog table?

  1. 3.70 in. wg
  2. 4.53 in. wg
  3. 6.00 in. wg
  4. 9.74 in. wg
Show Answer

The correct answer is D. The density ratio is d = 1.00 × 530 ÷ (400 + 460) = 0.616. The standard-air pressure is the actual pressure divided by d: 6.0 ÷ 0.616 = 9.74 in. wg. Option A multiplies by d instead of dividing. Option B uses 400 instead of 860 in the temperature term, forgetting the conversion to absolute temperature. Option C skips the correction. Airflow is read unchanged, and table BHP is multiplied by d to get hot power.

Concept Tested: Fan Selection

See: Fan Selection: From Duty Point to Catalog Size

4. A selection needs 1,500 RPM. If the fan were instead coupled directly to a 1,780 RPM four-pole motor on the same system with no VFD, what would happen according to the fan laws?

  1. About 19% more airflow and about 1.67 times the power
  2. About 19% more airflow and about 1.19 times the power
  3. About 19% more airflow and about 1.41 times the power
  4. The same airflow and about 1.67 times the power
Show Answer

The correct answer is A. The speed ratio is 1,780 ÷ 1,500 = 1.187. Airflow scales with the speed ratio, giving about 19% more air than the duty, and power scales with its cube: 1.187³ = 1.67. Option B scales power linearly, option C uses the square, and option D forgets that airflow also rises with speed. A belt drive or a VFD set to the required speed avoids this mismatch, which is why the fan laws are run before choosing direct drive.

Concept Tested: Drive Selection

See: Drive Selection

5. A fan's outlet sound power is 100 dB in the 63 Hz band and 90 dB in the 1,000 Hz band. The A-weighting corrections are −26.2 dB at 63 Hz and 0 dB at 1,000 Hz. Which band contributes more to the A-weighted overall level?

  1. The 63 Hz band, because it is 10 dB louder before weighting
  2. Neither, because the two bands contribute equally after weighting
  3. The 1,000 Hz band, at about 90 dB against about 73.8 dB for the 63 Hz band
  4. The 63 Hz band, because low frequencies pass through walls more easily
Show Answer

The correct answer is C. Each band is weighted before the bands are added: 100 − 26.2 = 73.8 dB at 63 Hz and 90 + 0 = 90 dB at 1,000 Hz. The 1,000 Hz band is about 16 dB higher after weighting, so it dominates the A-weighted total. Option A reads the unweighted levels, which the chapter warns against when comparing with an A-weighted limit. Low-frequency transmission (D) is a real concern for noise control but does not change the A-weighted arithmetic.

Concept Tested: Octave Band Sound Data

See: Octave Band Sound Data

6. A belt-driven SWSI fan handles 500°F gas, must sit directly on spring isolators on a mezzanine, and should be the shortest assembly that ships complete. Following FanPedia's arrangement descriptions, which arrangement fits best?

  1. Arrangement 4, with the impeller on the motor shaft
  2. Arrangement 9, with the motor on the side of the bearing pedestal
  3. Arrangement 9F, with an extended frame for the motor
  4. Arrangement 1, with the motor on a separate base
Show Answer

The correct answer is B. Arrangement 4 puts the motor against the hot housing, and FanPedia notes that high airstream temperatures may limit it. Arrangement 9F is not suitable for mounting isolators directly under the fan. Arrangement 1 keeps the bearings out of the gas but needs a separate motor base, which lengthens the assembly. Arrangement 9 hangs the motor on the side of the pedestal, keeps the assembly short and ships complete, provided the catalog confirms the motor frame fits.

Concept Tested: Arrangement Selection

See: Arrangement Selection

7. While reviewing a draft specification for a fan handling 500°F combustible dust, which pair of clauses cannot both be true?

  1. "Maximum operating temperature 500°F" and "Provide a shaft seal and shaft cooler"
  2. "Abrasive dust in the airstream" and "Provide a 7-gauge steel scroll liner, welded in place"
  3. "Mount the fan on spring isolators" and "Provide inlet and outlet flex connectors"
  4. "Maximum operating temperature 500°F" and "Provide AMCA Type B spark-resistant construction"
Show Answer

The correct answer is D. The RTF guide specification limits AMCA spark-resistance Types A and B to 250°F, so at 500°F only Type C applies; the two clauses contradict each other. The other pairs agree: a shaft seal and shaft cooler belong to the 500°F tier, a welded liner answers abrasive dust, and FanPedia requires flex connectors on all isolated fans. Most specification errors are two right-looking lines that cannot both be true, which is why review checks pairs.

Concept Tested: Specification Review

See: Specification Review

8. How does a complete fan description differ from a fan specification?

  1. The description states one fan from one manufacturer for the factory to build, while the specification states requirements, names a basis of design and may allow comparable products
  2. The description lists only the duty point, while the specification lists only construction features and accessories
  3. The description is written in CSI three-part format, while the specification is a single quote line on the fan schedule
  4. The description is prepared after installation, while the specification is prepared before bidding
Show Answer

The correct answer is A. A complete fan description is the compact, ordered statement of every attribute the factory needs to build one fan, and it is complete when two readers would build the same fan. A fan specification tells bidders what the fan must do and how it must be built, tested, documented and installed, so any compliant product is acceptable. Option C reverses the formats, and both documents include the duty point (B). Both are written before the fan is ordered (D).

Concept Tested: Complete Fan Description

See: Fan Specification

9. Which specification sentence best lets a reviewer prove from the submittal whether the high temperature requirement is met?

  1. "Fan shall be suitable for high temperature."
  2. "Fan shall be suitable for 500°F."
  3. "Maximum operating temperature: 500°F (260°C). Provide high temperature grease and bearings, shaft seal and shaft cooler."
  4. "Fan shall be of heavy-duty high temperature construction per the manufacturer's standard."
Show Answer

The correct answer is C. It states the condition and the required features, so each item can be checked against a submittal line by line, following the Twin City Fan guide specification's wording. Option A names no temperature and no construction. Option B names the temperature, but a bidder can omit the shaft cooler and still argue the fan is "suitable." Option D hands the definition to the bidder. The test for every sentence is whether a reviewer could prove compliance from the submittal.

Concept Tested: Fan Specification

See: Fan Specification

10. You are composing the performance clause for the dryer exhaust fan (20,000 ACFM at 12.0 in. wg, 500°F gas, sea level, 70°F cold start, 95 dB A-weighted outlet limit). Which draft is complete?

  1. Fan shall deliver 20,000 ACFM at 12.0 in. wg with 500°F gas at sea level, rated per AMCA 210 and certified under AMCA 211; motor sized for a 70°F start; outlet sound power not over 95 dB A-weighted, tested per AMCA 300 in eight octave bands.
  2. Fan shall deliver 20,000 CFM at 12.0 in. wg static pressure, rated per AMCA 210 and certified under AMCA 211; motor sized for the brake horsepower; outlet sound power not over 95 dB A-weighted.
  3. Fan shall deliver 20,000 ACFM at 12.0 in. wg at standard air, rated per AMCA 210; motor sized for the operating brake horsepower at 500°F; outlet sound power not over 95 dB A-weighted.
  4. Fan shall deliver 20,000 ACFM at 12.0 in. wg with 500°F gas at sea level, rated per AMCA 210; motor sized for a 70°F start; sound not over 95 dBA overall measured 5 ft from the fan.
Show Answer

The correct answer is A. A complete performance clause states the airflow and pressure, the air temperature and elevation at which they apply, the rating standards, and the limits on power and sound in a provable form. Option B gives no air condition, so a bidder could rate the fan at standard air. Option C states standard air and sizes the motor for the hot condition, which overloads on a cold start. Option D asks for sound pressure at a distance instead of octave band sound power per AMCA 300.

Concept Tested: Specification Performance Clause

See: Specification Performance Clause