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NEBB Testing, Adjusting and Balancing Certified Technician (CT) study materials
NEBB Testing, Adjusting and Balancing Certified Technician (CT) study resources

NEBB Testing, Adjusting and Balancing Certified Technician (CT) practice questions

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Question 1Air Systems Testing, Adjusting and Balancing

In a duct, the total pressure at a point is equal to which of the following?

  1. Velocity pressure minus static pressure
  2. Static pressure divided by velocity pressure
  3. Velocity pressure squared plus static pressure
  4. Static pressure plus velocity pressure Correct answer.

Explanation

Total pressure is the sum of static pressure and velocity pressure at the same point. Static pressure pushes against the duct wall, while velocity pressure represents the kinetic energy of the moving air.

Question 2Air Systems Testing, Adjusting and Balancing

At standard air density (0.075 lb/ft³), a velocity pressure of 0.25 in. w.c. corresponds to approximately what duct velocity?

  1. 500 fpm
  2. 2,000 fpm Correct answer.
  3. 4,000 fpm
  4. 1,000 fpm

Explanation

At standard air, V (fpm) = 4005 × √VP, where VP is in in. w.c. Since √0.25 = 0.50, V = 4005 × 0.50 ≈ 2,000 fpm.

Question 3Air Systems Testing, Adjusting and Balancing

A pitot tube connected to a manometer measures velocity pressure by taking the difference between:

  1. velocity pressure and static pressure
  2. total pressure and static pressure Correct answer.
  3. total pressure at two different points
  4. static pressure and atmospheric pressure

Explanation

The pitot tube has a total-pressure port facing the flow and static-pressure ports that sense pressure normal to the flow. Connecting the two sides of a manometer gives the velocity pressure.

Question 4Air Systems Testing, Adjusting and Balancing

According to fan laws, if fan speed is increased from 800 to 1000 rpm, airflow changes by what factor?

  1. 0.64
  2. 1.25 Correct answer.
  3. 1.56
  4. 2.00

Explanation

For a constant-density fan, airflow varies directly with fan speed. The speed ratio is 1000/800 = 1.25, so airflow becomes 1.25 times the original.

Question 5Air Systems Testing, Adjusting and Balancing

A room measures 40 ft × 30 ft × 10 ft and receives 3,600 cfm. What is the air change rate?

  1. 12 ACH
  2. 18 ACH Correct answer.
  3. 6 ACH
  4. 36 ACH

Explanation

ACH = (cfm × 60) ÷ room volume. The room volume is 40 × 30 × 10 = 12,000 ft³, so (3,600 × 60) ÷ 12,000 = 18 ACH.

Question 6Air Systems Testing, Adjusting and Balancing

An air balancing hood (balometer) is used primarily to:

  1. measure airflow at a grille Correct answer.
  2. measure fan motor current
  3. measure duct leakage
  4. measure static pressure in a duct

Explanation

A balancing hood captures the entire discharge from a grille and measures airflow directly in cfm. It is not used for internal duct traverses, static pressure, or leakage testing.

Question 7Air Systems Testing, Adjusting and Balancing

In proportional balancing, branch dampers are adjusted so that each branch:

  1. is fully open at final conditions
  2. reaches design flow before the next branch
  3. has the lowest possible static pressure
  4. has the same percent of design flow Correct answer.

Explanation

Proportional balancing adjusts branch dampers so every branch operates at the same percentage of its design airflow. The main damper or fan speed is then used to bring the whole system to 100%.

Question 8Air Systems Testing, Adjusting and Balancing

Static pressure in a duct should be measured with the sensing port:

  1. facing directly into the airflow
  2. perpendicular to airflow Correct answer.
  3. pointing downstream with the airflow
  4. at a 45-degree angle to airflow

Explanation

Static pressure acts perpendicular to the duct wall and to the direction of flow. A port facing into the airstream would sense total pressure, which includes velocity pressure.

Question 9Air Systems Testing, Adjusting and Balancing

For a duct traverse, the preferred straight duct length is approximately:

  1. 7.5 diameters downstream and 3 upstream Correct answer.
  2. 2 diameters downstream and 1 upstream
  3. 1 diameter downstream and 1 upstream
  4. 3 diameters downstream and 7.5 upstream

Explanation

Traverses are taken in a straight section far enough from fittings to limit turbulence. A common guideline is at least 7.5 duct diameters downstream and 3 diameters upstream of the traverse.

Question 10Air Systems Testing, Adjusting and Balancing

A duct is moving 4,000 cfm of air at density 0.070 lb/ft³. What is the equivalent standard airflow (0.075 lb/ft³)?

  1. 4,000 cfm
  2. 3,733 cfm Correct answer.
  3. 4,286 cfm
  4. 3,500 cfm

Explanation

Mass flow is constant, so standard cfm = actual cfm × (actual density ÷ 0.075). Thus 4,000 × (0.070 ÷ 0.075) ≈ 3,733 cfm.

Question 11Air Systems Testing, Adjusting and Balancing

If fan speed is increased by 20%, the fan static pressure changes by approximately:

  1. 44% increase Correct answer.
  2. 72.8% increase
  3. 20% decrease
  4. 20% increase

Explanation

Fan static pressure varies with the square of the speed ratio. A 20% speed increase gives 1.20² = 1.44, or a 44% increase in pressure.

Question 12Air Systems Testing, Adjusting and Balancing

If fan speed is doubled, fan power changes by what factor?

  1. 4
  2. 16
  3. 2
  4. 8 Correct answer.

Explanation

Fan power varies with the cube of the speed ratio. Doubling speed gives 2³ = 8 times the power.

Question 13Air Systems Testing, Adjusting and Balancing

System effect in a fan installation is caused primarily by:

  1. using a VFD instead of a starter
  2. a dirty air filter downstream of the fan
  3. operating the fan below design rpm
  4. poor fan inlet or outlet connections Correct answer.

Explanation

System effect is a loss caused by poor airflow patterns at the fan inlet or outlet, such as elbows or restrictions mounted too close. It reduces the fan's usable performance compared with factory test conditions.

Question 14Air Systems Testing, Adjusting and Balancing

Which damper blade arrangement is generally preferred for modulating airflow with a more linear relationship between blade position and flow?

  1. Parallel blade dampers
  2. Radial blade dampers
  3. Opposed blade dampers Correct answer.
  4. Single-blade dampers

Explanation

Opposed-blade dampers move in opposite directions, keeping the flow area more centered and producing a more linear modulation characteristic. Parallel-blade dampers tend to deflect airflow toward one side.

Question 15Air Systems Testing, Adjusting and Balancing

A VAV terminal box has a minimum airflow setpoint of 30% of design. If design airflow is 1,200 cfm, what is the minimum airflow?

  1. 400 cfm
  2. 120 cfm
  3. 360 cfm Correct answer.
  4. 300 cfm

Explanation

Minimum airflow = 0.30 × 1,200 cfm = 360 cfm. The VAV box must not modulate below this value under normal control.

Question 16Air Systems Testing, Adjusting and Balancing

Outside air is 40°F, return air is 75°F, and mixed air is 65°F. What percentage of the mixed air is outside air?

  1. 29% Correct answer.
  2. 40%
  3. 57%
  4. 20%

Explanation

The outside-air fraction is (mixed-air temperature − return-air temperature) ÷ (outside-air temperature − return-air temperature). That is (65 − 75) ÷ (40 − 75) = 0.286, or about 29%.

Question 17Air Systems Testing, Adjusting and Balancing

A cooling coil has a face area of 20 ft² and handles 8,000 cfm. What is the face velocity?

  1. 250 fpm
  2. 800 fpm
  3. 160 fpm
  4. 400 fpm Correct answer.

Explanation

Face velocity = airflow ÷ coil face area. 8,000 cfm ÷ 20 ft² = 400 fpm.

Question 18Air Systems Testing, Adjusting and Balancing

Duct leakage class is typically expressed as:

  1. inches of water per 100 feet of duct
  2. percentage of fan motor horsepower
  3. cfm per 100 ft² at test pressure Correct answer.
  4. cfm per linear foot at design airflow

Explanation

Duct leakage is quantified in cfm per 100 ft² of duct surface at a specified test pressure. This allows duct of different sizes to be compared on the same basis.

Question 19Air Systems Testing, Adjusting and Balancing

When performing a pitot-tube traverse in a round duct, the number of measurement points is generally selected based on:

  1. the fan motor horsepower and drive type
  2. duct diameter and log-linear spacing Correct answer.
  3. the duct static pressure at the fan
  4. the air temperature only

Explanation

The number of traverse points is set by duct size and the accuracy needed, usually with a log-linear or equal-area layout. More points are needed in larger ducts to represent the velocity profile.

Question 20Air Systems Testing, Adjusting and Balancing

A fan operating point is the intersection of:

  1. the static pressure and velocity pressure curves
  2. the design airflow line and motor curve
  3. the fan curve and the system curve Correct answer.
  4. the duct leakage curve and the fan curve

Explanation

The fan curve shows the pressure the fan can produce at each airflow; the system curve shows the pressure required by the duct system. Their intersection is the actual operating point.

Question 21Air Systems Testing, Adjusting and Balancing

A coil handles 2,000 cfm and the air temperature rises 18°F. Using Qs = 1.08 × cfm × ΔT, what is the sensible heat gain?

  1. 38,900 Btu/h Correct answer.
  2. 21,600 Btu/h
  3. 36,000 Btu/h
  4. 43,200 Btu/h

Explanation

The sensible heat equation is Qs = 1.08 × cfm × ΔT. Here 1.08 × 2,000 × 18 = 38,880 Btu/h, approximately 38,900 Btu/h.

Question 22Air Systems Testing, Adjusting and Balancing

A duct traverse yields velocity pressures of 0.16, 0.25, 0.36, and 0.49 in. w.c. What is the average velocity at standard air?

  1. 1,800 fpm
  2. 2,002 fpm
  3. 2,404 fpm
  4. 2,203 fpm Correct answer.

Explanation

Velocity is found for each point from V = 4005√VP, then the velocities are averaged. The four velocities are about 1,602, 2,003, 2,403, and 2,804 fpm, averaging about 2,203 fpm.

Question 23Air Systems Testing, Adjusting and Balancing

A fan delivers 10,000 cfm at 2.0 in. w.c. static pressure. If a system damper is partially closed, the operating airflow will:

  1. remain the same because speed is unchanged
  2. increase until the fan curve is reached
  3. increase because fan static pressure rises
  4. decrease at a higher fan static pressure Correct answer.

Explanation

Partially closing a damper adds resistance to the system, steepening the system curve. The operating point moves to a lower airflow and a higher fan static pressure.

Question 24Air Systems Testing, Adjusting and Balancing

A velocity pressure reading of 0.09 in. w.c. is taken in air at 0.060 lb/ft³. What is the actual velocity?

  1. 1,500 fpm
  2. 1,096 fpm
  3. 1,342 fpm Correct answer.
  4. 1,202 fpm

Explanation

At nonstandard density, V = 1096 × √(VP ÷ density). Thus 1096 × √(0.09 ÷ 0.060) = 1096 × 1.225 ≈ 1,342 fpm.

Question 25Air Systems Testing, Adjusting and Balancing

After a proportional balance has brought all branches to the same percentage of design airflow, the final step is to:

  1. re-traverse the main duct and reset the fan curve
  2. adjust main damper or fan speed to 100% Correct answer.
  3. close the branch with the lowest percentage
  4. fully open all branch dampers

Explanation

Once all branches share the same percentage of design, they are proportionally correct relative to one another. The final adjustment is made at the main damper or fan speed to bring all branches to 100% design.

Question 26Air Systems Testing, Adjusting and Balancing

Total pressure in a duct is equal to which combination of pressures?

  1. Static pressure minus velocity pressure
  2. Static pressure plus velocity pressure Correct answer.
  3. Velocity pressure minus static pressure
  4. Static pressure multiplied by velocity pressure

Explanation

Total pressure is the sum of the static pressure and the velocity pressure at the same point in the duct. Static pressure acts against the duct walls, while velocity pressure represents the kinetic energy of the moving air. Total pressure is the quantity that decreases in the direction of flow because of friction and dynamic losses.

Question 27Air Systems Testing, Adjusting and Balancing

The main function of a volume damper installed in a branch duct is to:

  1. Remove dust from the supply air
  2. Regulate branch airflow Correct answer.
  3. Measure the duct velocity pressure
  4. Increase the fan motor speed

Explanation

A volume damper introduces a controllable resistance in the branch so the airflow can be adjusted to design. Balancing technicians use it to throttle or open the branch during proportional balancing. It does not change fan speed, filter air, or measure velocity.

Question 28Air Systems Testing, Adjusting and Balancing

At standard air conditions, duct velocity in feet per minute is calculated from velocity pressure using which expression?

  1. 4005 × Vp
  2. 4005 × √Vp Correct answer.
  3. Vp ÷ 4005
  4. 4005 × Vp²

Explanation

The standard-air velocity equation is V = 4005 times the square root of velocity pressure in inches of water column. The constant 4005 applies at a density of 0.075 lb/ft³. A density correction is needed when the air is at a different density.

Question 29Air Systems Testing, Adjusting and Balancing

A branch duct has a design airflow of 1,000 cfm. The balancing hood measures 950 cfm. What is the deviation from design?

  1. 5 percent above design
  2. 5 percent below design Correct answer.
  3. 3 percent below design
  4. 10 percent below design

Explanation

Deviation is calculated as the difference between measured and design airflow divided by design airflow: (1,000 − 950) ÷ 1,000 = 0.05, or 5 percent. Because the measured value is lower than design, the branch is 5 percent below design.

Question 30Air Systems Testing, Adjusting and Balancing

A heating coil handles 1,500 cfm with an air temperature rise of 25°F. Using Qs = 1.08 × cfm × ΔT, what is the sensible heat output?

  1. 40,500 Btu/h Correct answer.
  2. 27,000 Btu/h
  3. 16,200 Btu/h
  4. 54,000 Btu/h

Explanation

Substituting into the sensible heat equation gives Qs = 1.08 × 1,500 × 25. The product is 40,500 Btu/h. The factor 1.08 applies to standard air at sea level.

Question 31Air Systems Testing, Adjusting and Balancing

A room is supplied with 500 cfm and has 400 cfm of return air. To maintain the room at a neutral pressure relative to adjacent spaces, how much air must be exhausted from the room?

  1. 400 cfm
  2. 900 cfm
  3. 100 cfm Correct answer.
  4. 0 cfm

Explanation

For neutral room pressure, supply airflow must equal the sum of return and exhaust airflow. The exhaust required is therefore 500 − 400 = 100 cfm. Returning all 500 cfm or exhausting none would change the room pressure relationship.

Question 32Air Systems Testing, Adjusting and Balancing

Static pressure in a duct is 1.2 in. w.c. at the fan outlet and 0.4 in. w.c. at a point 50 ft downstream. What is the friction rate per 100 ft of duct?

  1. 2.4 in. w.c. per 100 ft
  2. 1.2 in. w.c. per 100 ft
  3. 1.6 in. w.c. per 100 ft Correct answer.
  4. 0.8 in. w.c. per 100 ft

Explanation

The pressure drop over the 50 ft section is 1.2 − 0.4 = 0.8 in. w.c. Scaling this to 100 ft gives 0.8 × (100 ÷ 50) = 1.6 in. w.c. per 100 ft. Friction rate is normally expressed per 100 ft of equivalent duct length.

Question 33Air Systems Testing, Adjusting and Balancing

A pitot-tube reading shows a velocity pressure of 0.20 in. w.c. in air with a density of 0.070 lb/ft³. What is the actual duct velocity?

  1. 1,650 fpm
  2. 1,850 fpm Correct answer.
  3. 1,100 fpm
  4. 1,400 fpm

Explanation

For air densities other than standard, velocity is found from V = 1096.2 × √(Vp ÷ ρ). Here V = 1096.2 × √(0.20 ÷ 0.070) ≈ 1,850 fpm. The lower density increases the velocity for a given velocity pressure compared with standard air.

Question 34Air Systems Testing, Adjusting and Balancing

A 20 in. diameter round duct has an average velocity pressure of 0.30 in. w.c. at an air density of 0.072 lb/ft³. What is the approximate airflow?

  1. 2,450 cfm
  2. 4,900 cfm Correct answer.
  3. 3,500 cfm
  4. 6,100 cfm

Explanation

The duct area is π × (10 ÷ 12)² ≈ 2.18 ft². Velocity is V = 1096.2 × √(0.30 ÷ 0.072) ≈ 2,240 fpm, so airflow is about 2.18 × 2,240 ≈ 4,900 cfm. Both the density correction and the duct area must be applied.

Question 35Hydronic Systems Testing, Adjusting and Balancing

A circulator operating at 1200 rpm delivers 400 gpm. With the same impeller, reducing the speed to 900 rpm will produce approximately:

  1. 225 gpm
  2. 400 gpm
  3. 300 gpm Correct answer.
  4. 533 gpm

Explanation

The pump affinity laws make flow proportional to rotational speed, so the new flow is 400 gpm times 900/1200, or 300 gpm.

Question 36Hydronic Systems Testing, Adjusting and Balancing

A pump producing 500 gpm at 64 ft of head is slowed to 75% of its original speed. The head at the new speed is approximately:

  1. 36 ft Correct answer.
  2. 48 ft
  3. 27 ft
  4. 64 ft

Explanation

Head varies with the square of the speed ratio, so 0.75 squared equals 0.5625 and 0.5625 times 64 ft is 36 ft.

Question 37Hydronic Systems Testing, Adjusting and Balancing

The cold fill pressure of a closed hydronic system is normally set so that:

  1. pressure at the highest point stays about 4 psi above atmosphere Correct answer.
  2. tank precharge equals the pump shutoff head
  3. pump suction pressure equals the static height
  4. pump discharge pressure equals the design head

Explanation

Fill pressure must equal the static height of the system plus a small margin, usually about 4 psi, at the highest point so that positive pressure is maintained there and air can be vented.

Question 38Hydronic Systems Testing, Adjusting and Balancing

In a hot water system, the air separator is best located:

  1. at the hottest, lowest-pressure point, near the boiler outlet Correct answer.
  2. at the lowest point, just downstream of the expansion tank
  3. at the highest point of the distribution piping
  4. on the pump discharge at the point of highest pressure

Explanation

Air comes out of solution most readily where the water is hottest and the pressure is lowest, so the separator is placed near the boiler outlet on the suction side of the pump.

Question 39Hydronic Systems Testing, Adjusting and Balancing

A technician reads 13 psi on the pump discharge gauge and 5 psi on the suction gauge. The pump head is approximately:

  1. 8 ft
  2. 18.5 ft Correct answer.
  3. 30 ft
  4. 42 ft

Explanation

Pump head is the difference between discharge and suction pressure, 8 psi, converted to feet of water by multiplying by 2.31, which gives about 18.5 ft.

Question 40Hydronic Systems Testing, Adjusting and Balancing

A balancing valve has a published Cv of 5.0. With 4 psi measured across the valve, the flow through it is:

  1. 2.5 gpm
  2. 20 gpm
  3. 1.25 gpm
  4. 10 gpm Correct answer.

Explanation

For water, flow equals Cv times the square root of the pressure drop in psi, so 5.0 times the square root of 4 equals 10 gpm.

Question 41Hydronic Systems Testing, Adjusting and Balancing

A system balanced on water is later filled with a 30% propylene glycol solution. To deliver the same capacity at the same temperature difference, the technician should:

  1. reduce flow in proportion to the higher viscosity
  2. increase flow to offset the lower specific heat of the mixture Correct answer.
  3. make no change, because glycol does not affect coil capacity
  4. lower the pump speed to avoid over-pumping

Explanation

Glycol solutions carry less heat per gallon per degree than water because their specific heat is lower, so flow must be increased to move the same Btu; viscosity also raises head, which is handled separately.

Question 42Hydronic Systems Testing, Adjusting and Balancing

A chilled water coil balanced to design flow shows a 6 degrees F water temperature rise where design is 12 degrees F, with the control valve fully open. The most likely cause is:

  1. the thermometer wells are dry
  2. the strainer upstream is partly plugged
  3. the coil is not loaded to design capacity Correct answer.
  4. the coil is air bound on the water side

Explanation

At design water flow, the water temperature difference tracks the actual load, so half the design difference indicates roughly half the design load; flow-related faults would first show up as a flow shortfall.

Question 43Hydronic Systems Testing, Adjusting and Balancing

Which distribution layout tends to deliver nearly equal flow to each terminal without individual balancing valves?

  1. two-pipe with a common return header at the near end
  2. reverse return Correct answer.
  3. direct return from a single main
  4. one-pipe series loop

Explanation

In a reverse return layout the supply and return paths to each terminal are approximately equal in length, so pressure drops are similar and flows tend to self-balance.

Question 44Hydronic Systems Testing, Adjusting and Balancing

A three-way valve piped to a terminal coil is used primarily to:

  1. balance the coil automatically to design flow
  2. hold total system flow nearly constant while coil flow varies Correct answer.
  3. vary coil flow while total system flow falls with load
  4. isolate the coil for service

Explanation

A three-way valve diverts water around or through the coil so that coil flow modulates while the total quantity of water circulating in the loop stays nearly constant.

Question 45Hydronic Systems Testing, Adjusting and Balancing

A primary-secondary system has 400 gpm in the primary loop while the secondary pump throttles back to 300 gpm. The decoupler will carry:

  1. no flow, because the loops are hydraulically separated
  2. 100 gpm from the primary supply to the primary return Correct answer.
  3. 300 gpm in the same direction as the secondary flow
  4. 100 gpm from the secondary return into the primary supply

Explanation

When primary flow exceeds secondary flow, the surplus primary water cannot enter the secondary loop, so it passes through the decoupler from supply back to return; the difference in flow is the decoupler flow.

Question 46Hydronic Systems Testing, Adjusting and Balancing

In a variable-flow system controlled by a differential pressure sensor, the sensor is normally located:

  1. across the hydraulically most remote terminal or its branch Correct answer.
  2. across the pump so that it reads pump head
  3. at the terminal closest to the pump
  4. at the expansion tank connection

Explanation

The sensor is placed on the index circuit so that the pump maintains just enough pressure at the hardest-to-feed terminal while permitting flow elsewhere to fall.

Question 47Hydronic Systems Testing, Adjusting and Balancing

Cavitation in a hydronic circulator is most often the result of:

  1. insufficient absolute pressure at the pump suction Correct answer.
  2. excessive discharge pressure
  3. throttling of a balance valve downstream of the pump
  4. an oversized impeller for the duty

Explanation

Cavitation occurs when local absolute pressure at the suction eye drops below the vapor pressure of the water, so the liquid flashes and then collapses, damaging the impeller.

Question 48Hydronic Systems Testing, Adjusting and Balancing

The expansion tank, which establishes the point of no pressure change, should be connected:

  1. at the pump suction, close to the pump Correct answer.
  2. at the highest point of the system
  3. at the discharge side of the pump
  4. at the far end of the supply main

Explanation

Connecting the tank at the pump suction fixes the pressure there, so the pump head acts to raise pressure throughout the system rather than being absorbed by the tank.

Question 49Hydronic Systems Testing, Adjusting and Balancing

Before a clamp-on ultrasonic flow meter can give a reliable reading, the technician must:

  1. remove insulation only when the pipe exceeds 4 in.
  2. install a straightening vane downstream of the transducers
  3. program pipe size, wall and material, and mount with adequate straight run Correct answer.
  4. shut down the pump so that flow stops

Explanation

Transit-time ultrasonic meters compute flow from the acoustic path, so pipe geometry, wall thickness and material must be entered and the transducers placed where the velocity profile is fully developed.

Question 50Hydronic Systems Testing, Adjusting and Balancing

A control valve selected with a valve authority of about 0.15 will:

  1. eliminate the need for a balancing valve in the branch
  2. be oversized for the coil and hunt at all loads
  3. modulate linearly with coil load
  4. have a distorted installed characteristic and poor control at part load Correct answer.

Explanation

Valve authority is the wide-open valve pressure drop divided by the variable branch pressure drop; a low value means the coil and fittings dominate, distorting the installed characteristic and making part-load control unstable.