Page 1 of 146
NAFA Certified Air Filter Specialist (CAFS) EXAM
Questions with Correct Answers and explanations
LATEST THIS YEAR -JUST RELEASED
Summarized Exam Coverage – NAFA CAFS Exam
The exam covers basic units and particle sizes, air composition, aerosol science, filtration mechanisms
(impingement, interception, straining, diffusion), particle counters and measurement, filter types
(mechanical, electronic, HEPA/ULPA), ASHRAE standards (52.2, 62.1/62.2), MERV ratings, pressure drop
and velocity relationships, IAQ principles, gas-phase filtration, UVGI technology, PCO (photocatalytic
oxidation) systems, dust collection equipment, electrostatic precipitators, and contamination control
principles .
1. A pressure gauge reading of negative 1.5 inches of water column on the suction side of a fan indicates
what condition relative to atmospheric pressure?
A) The pressure is 1.5 psi above atmospheric
B) The pressure is 1.5 inches w.g. below atmospheric
C) The fan is operating in forward curve stall
D) The system has a major air leak downstream
Answer: B – Negative static pressure (suction) is measured below atmospheric pressure; 1.5 inches w.g.
negative is a common filter loading indicator.
2. A hospital operating room requires a filter capable of 99.97% efficiency on 0.3 micrometer particles.
What specific filter classification must be specified for this critical application?
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A) MERV 16
B) ULPA
C) HEPA
D) MERV 14
Answer: C – HEPA filters are defined as achieving 99.97% efficiency on 0.3 µm particles. ULPA is 99.999%
on 0.12 µm.
3. An air filtration specialist is designing a system for a museum archive containing sensitive paper
artifacts. Besides particulate filtration, what additional contaminant control is most critical for
preventing acid-based degradation of cellulose materials?
A) High-voltage electrostatic precipitation
B) Activated carbon chemisorption for sulfur dioxide and nitrogen oxides
C) UVGI sterilization to prevent mold growth
D) Mist elimination for humidity control
Answer: B – Paper degradation is accelerated by acidic gases (SO₂, NOₓ); chemisorption using treated
activated carbon or potassium permanganate media is required.
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4. A technician measures a filter's initial resistance at 0.30 inches w.g. at 1,000 CFM. After six months, at
the same airflow, the resistance is 1.20 inches w.g. The system fan is constant speed. What has
happened to the volumetric flow rate delivered to the conditioned space?
A) It has increased by approximately 25%
B) It has decreased by approximately 25%
C) It has decreased by approximately 50%
D) It has remained constant because the fan speed did not change
Answer: C – With a constant speed fan, increased filter resistance shifts the system operating point left
on the fan curve. At double the original resistance (from 0.30 to 1.20), airflow drops significantly.
5. A particle that follows the airstream but still contacts a filter fiber as it passes around it is captured by
which of the four primary filtration mechanisms?
A) Straining
B) Impingement
C) Interception
D) Diffusion
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Answer: C – Interception occurs when a particle follows the air streamline but its physical radius touches
the fiber even though the streamline does not intersect the fiber .
6. A building owner wants to install air cleaners to remove cooking odors from a commercial kitchen
exhaust. Which type of gas-phase filtration media is most cost-effective for removing the volatile
organic compounds (VOCs) present in cooking fumes?
A) Ultraviolet germicidal irradiation
B) Activated carbon adsorption
C) Electrostatic precipitation
D) High-efficiency particulate arrestance filters
Answer: B – Activated carbon is the standard media for VOC adsorption in commercial kitchen and
industrial exhaust applications.
7. The fan static pressure in a constant volume HVAC system is measured at 2.5 inches w.g. After
installing new high-efficiency filters, the static pressure increases to 3.8 inches w.g. The fan motor
amperage increases by 15%. What is the most likely operational consequence if no other changes are
made?
NAFA Certified Air Filter Specialist (CAFS) EXAM
Questions with Correct Answers and explanations
LATEST THIS YEAR -JUST RELEASED
Summarized Exam Coverage – NAFA CAFS Exam
The exam covers basic units and particle sizes, air composition, aerosol science, filtration mechanisms
(impingement, interception, straining, diffusion), particle counters and measurement, filter types
(mechanical, electronic, HEPA/ULPA), ASHRAE standards (52.2, 62.1/62.2), MERV ratings, pressure drop
and velocity relationships, IAQ principles, gas-phase filtration, UVGI technology, PCO (photocatalytic
oxidation) systems, dust collection equipment, electrostatic precipitators, and contamination control
principles .
1. A pressure gauge reading of negative 1.5 inches of water column on the suction side of a fan indicates
what condition relative to atmospheric pressure?
A) The pressure is 1.5 psi above atmospheric
B) The pressure is 1.5 inches w.g. below atmospheric
C) The fan is operating in forward curve stall
D) The system has a major air leak downstream
Answer: B – Negative static pressure (suction) is measured below atmospheric pressure; 1.5 inches w.g.
negative is a common filter loading indicator.
2. A hospital operating room requires a filter capable of 99.97% efficiency on 0.3 micrometer particles.
What specific filter classification must be specified for this critical application?
, Page 2 of 146
A) MERV 16
B) ULPA
C) HEPA
D) MERV 14
Answer: C – HEPA filters are defined as achieving 99.97% efficiency on 0.3 µm particles. ULPA is 99.999%
on 0.12 µm.
3. An air filtration specialist is designing a system for a museum archive containing sensitive paper
artifacts. Besides particulate filtration, what additional contaminant control is most critical for
preventing acid-based degradation of cellulose materials?
A) High-voltage electrostatic precipitation
B) Activated carbon chemisorption for sulfur dioxide and nitrogen oxides
C) UVGI sterilization to prevent mold growth
D) Mist elimination for humidity control
Answer: B – Paper degradation is accelerated by acidic gases (SO₂, NOₓ); chemisorption using treated
activated carbon or potassium permanganate media is required.
, Page 3 of 146
4. A technician measures a filter's initial resistance at 0.30 inches w.g. at 1,000 CFM. After six months, at
the same airflow, the resistance is 1.20 inches w.g. The system fan is constant speed. What has
happened to the volumetric flow rate delivered to the conditioned space?
A) It has increased by approximately 25%
B) It has decreased by approximately 25%
C) It has decreased by approximately 50%
D) It has remained constant because the fan speed did not change
Answer: C – With a constant speed fan, increased filter resistance shifts the system operating point left
on the fan curve. At double the original resistance (from 0.30 to 1.20), airflow drops significantly.
5. A particle that follows the airstream but still contacts a filter fiber as it passes around it is captured by
which of the four primary filtration mechanisms?
A) Straining
B) Impingement
C) Interception
D) Diffusion
, Page 4 of 146
Answer: C – Interception occurs when a particle follows the air streamline but its physical radius touches
the fiber even though the streamline does not intersect the fiber .
6. A building owner wants to install air cleaners to remove cooking odors from a commercial kitchen
exhaust. Which type of gas-phase filtration media is most cost-effective for removing the volatile
organic compounds (VOCs) present in cooking fumes?
A) Ultraviolet germicidal irradiation
B) Activated carbon adsorption
C) Electrostatic precipitation
D) High-efficiency particulate arrestance filters
Answer: B – Activated carbon is the standard media for VOC adsorption in commercial kitchen and
industrial exhaust applications.
7. The fan static pressure in a constant volume HVAC system is measured at 2.5 inches w.g. After
installing new high-efficiency filters, the static pressure increases to 3.8 inches w.g. The fan motor
amperage increases by 15%. What is the most likely operational consequence if no other changes are
made?
