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CA C-20 HVAC study materials
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CA C-20 HVAC practice questions

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Question 1Planning, Layout, and Estimating

In residential HVAC planning, a Manual J calculation is performed primarily to determine which of the following?

  1. The filter efficiency rating
  2. The refrigerant charge for the system
  3. Heating and cooling load Correct answer.
  4. The supply register locations

Explanation

Manual J is the accepted residential method for calculating room-by-room heating and cooling loads from envelope, infiltration, and internal gain data. Those loads then drive equipment selection, duct design, and room-by-room sizing.

Question 2Planning, Layout, and Estimating

Supply ductwork routed through an unconditioned attic is insulated primarily to accomplish which of the following?

  1. Provide structural support for the duct
  2. Increase the static pressure in the duct
  3. Reduce the noise produced at the register
  4. Control heat gain and condensation Correct answer.

Explanation

Insulation slows heat transfer between the duct and the attic air and keeps the duct surface above the dew point, preventing condensation. Duct insulation does not carry structural, acoustic, or pressure duties.

Question 3Planning, Layout, and Estimating

When laying out a mechanical room, the clearance left in front of a furnace is intended mainly to provide which of the following?

  1. Room for a condensate pump
  2. Space for future duct additions
  3. Service and maintenance access Correct answer.
  4. A thermal buffer from the wall

Explanation

Manufacturer clearances and mechanical codes require working space in front of equipment so technicians can remove panels, service burners, and replace components safely. The required dimension comes from the installation manual and local code.

Question 4Planning, Layout, and Estimating

A floor plan is drawn at a scale of 1/4 inch = 1 foot. A duct run measures 3 inches on the drawing. What is its actual length?

  1. 6 feet
  2. 9 feet
  3. 8 feet
  4. 12 feet Correct answer.

Explanation

Each 1/4 inch on the drawing represents 1 foot, so 3 inches contains twelve 1/4-inch units. Multiplying 12 by 1 foot gives an actual length of 12 feet.

Question 5Planning, Layout, and Estimating

The U-factor of a building assembly is best described as which of the following?

  1. The reciprocal of total R-value Correct answer.
  2. The sum of the R-values of the layers
  3. The thickness of the insulation
  4. The vapor permeability of the assembly

Explanation

U-factor is the overall conductance of an assembly and equals 1 divided by the total R-value, including surface films and all layers. It is used directly with area and temperature difference in heat transfer calculations.

Question 6Planning, Layout, and Estimating

Which rating expresses the annual heating efficiency of a gas furnace?

  1. SEER2
  2. HSPF2
  3. AFUE Correct answer.
  4. EER2

Explanation

AFUE (annual fuel utilization efficiency) is the federally defined efficiency metric for furnaces and boilers. It accounts for both steady-state efficiency and off-cycle losses over a heating season.

Question 7Planning, Layout, and Estimating

In a traditional trunk-and-branch duct layout, the trunk line is best described as which of the following?

  1. The smallest duct in the system
  2. The duct that connects only to the return grille
  3. The main duct feeding the branch runs Correct answer.
  4. The flexible connector at the air handler

Explanation

The trunk is the main distribution duct that carries the full or partial air volume and feeds smaller branch runs to individual rooms. Branch ducts are sized for the room load served.

Question 8Planning, Layout, and Estimating

A confined mechanical closet containing a natural-draft gas furnace must be provided with combustion air primarily to do which of the following?

  1. Pressurize the closet above the return duct pressure
  2. Support complete combustion and proper venting Correct answer.
  3. Reduce the flue gas temperature
  4. Cool the furnace heat exchanger

Explanation

Fuel-burning appliances need a reliable supply of air for combustion and for draft dilution so the flue gases leave the appliance properly. Code-prescribed openings or ducted outside air prevent negative pressure and incomplete combustion.

Question 9Planning, Layout, and Estimating

A duct system is sized using the equal-friction method at 0.10 in. w.c. per 100 ft. If the total effective length of the longest run is 200 ft, what total friction loss should be budgeted for that run?

  1. 0.20 in. w.c. Correct answer.
  2. 0.10 in. w.c.
  3. 0.05 in. w.c.
  4. 0.40 in. w.c.

Explanation

The friction rate is applied per 100 ft of effective length, so 200 ft is two 100-ft increments. Multiplying 0.10 in. w.c. by 2 gives 0.20 in. w.c. for the run.

Question 10Planning, Layout, and Estimating

A duct run has 120 ft of straight duct and fittings whose equivalent length totals 30 ft. Using 0.08 in. w.c. per 100 ft of effective length, what is the friction loss?

  1. 0.12 in. w.c. Correct answer.
  2. 0.096 in. w.c.
  3. 0.24 in. w.c.
  4. 0.15 in. w.c.

Explanation

Effective length equals straight length plus fitting equivalent length, or 150 ft. At 0.08 in. w.c. per 100 ft, the loss is 0.08 times 1.5, which equals 0.12 in. w.c.

Question 11Planning, Layout, and Estimating

A split-system air conditioner is installed with a vertical riser of 25 ft to the indoor coil. Which design consideration becomes most important for the suction line?

  1. Adding a filter drier at the outdoor unit
  2. Increasing the liquid line size to reduce flash gas
  3. Reducing the condenser coil face area
  4. Maintaining oil return velocity Correct answer.

Explanation

On a tall vertical riser, refrigerant velocity must stay high enough to carry compressor oil upward and back to the compressor. Line sizing and occasionally an oil trap are selected with this in mind.

Question 12Planning, Layout, and Estimating

A specification requires 0.35 air changes per hour of outdoor ventilation for a 2,000 sq ft residence with 9 ft ceilings. What outdoor airflow is required?

  1. 140 cfm
  2. 70 cfm
  3. 105 cfm Correct answer.
  4. 90 cfm

Explanation

The house volume is 2,000 sq ft times 9 ft, or 18,000 cu ft. At 0.35 air changes per hour, that is 6,300 cu ft per hour, which divided by 60 minutes equals 105 cfm.

Question 13Planning, Layout, and Estimating

A blower must overcome 0.20 in. w.c. of supply static, 0.15 in. w.c. of return static, and a 0.10 in. w.c. allowance for the filter and coil. What total external static pressure must the blower be rated for?

  1. 0.25 in. w.c.
  2. 0.35 in. w.c.
  3. 0.55 in. w.c.
  4. 0.45 in. w.c. Correct answer.

Explanation

External static pressure is the sum of all resistances outside the fan: supply, return, and any filter or coil allowance. Adding 0.20, 0.15, and 0.10 gives 0.45 in. w.c.

Question 14Planning, Layout, and Estimating

A takeoff shows 14 supply registers at $38 each and 6 return grilles at $52 each. What is the material cost for the grilles and registers?

  1. $796
  2. $844 Correct answer.
  3. $780
  4. $912

Explanation

Supply registers cost 14 times $38, or $532, and return grilles cost 6 times $52, or $312. The combined material cost is $844.

Question 15Planning, Layout, and Estimating

An estimator uses a productivity rate of 12 ft of duct installed per labor hour. A project includes 480 ft of duct, and the loaded labor rate is $65 per hour. What is the estimated labor cost for the duct installation?

  1. $3,120
  2. $2,860
  3. $2,600 Correct answer.
  4. $2,400

Explanation

Dividing 480 ft by 12 ft per hour gives 40 labor hours. Multiplying 40 hours by $65 per hour yields $2,600.

Question 16Planning, Layout, and Estimating

A contractor applies a 15% overhead and then a 10% profit markup to a $20,000 material and labor cost. What is the resulting selling price?

  1. $25,300 Correct answer.
  2. $25,000
  3. $26,000
  4. $24,500

Explanation

Applying the markups sequentially, $20,000 times 1.15 equals $23,000, and $23,000 times 1.10 equals $25,300. Sequential markups compound rather than simply adding to 25%.

Question 17Planning, Layout, and Estimating

In a hydronic heating loop, water velocity in small-diameter piping is commonly limited to about 4 ft per second primarily for which reason?

  1. To reduce the expansion tank size
  2. To limit erosion, noise, and pressure drop Correct answer.
  3. To raise the supply water temperature
  4. To increase the pump head required

Explanation

Excessive velocity causes erosion-corrosion, flow noise, and a rapid rise in friction loss. Keeping velocity near 4 ft per second balances pipe size against pump energy.

Question 18Planning, Layout, and Estimating

Infiltration load in a residence is most directly driven by which combination of factors?

  1. Envelope leakage and pressure differences Correct answer.
  2. Refrigerant charge and coil surface area
  3. Register throw and room air changes
  4. Duct static pressure and blower fan speed

Explanation

Infiltration depends on how leaky the envelope is and on the pressure and temperature differences driving air through those leaks. Wind and stack effect are the usual driving forces.

Question 19Planning, Layout, and Estimating

A room requires 250 cfm, and the selected branch duct velocity is 700 fpm. What duct cross-sectional area is required?

  1. 36 sq in.
  2. 44 sq in.
  3. 62 sq in.
  4. 51 sq in. Correct answer.

Explanation

Area equals airflow divided by velocity, so 250 cfm divided by 700 fpm equals 0.357 sq ft. Multiplying by 144 gives about 51 sq in.

Question 20Planning, Layout, and Estimating

Duct leakage testing of a newly installed system is performed primarily to verify which of the following?

  1. That the fan motor is drawing the correct amperage
  2. That the duct system meets the leakage limit Correct answer.
  3. That the register airflow is balanced
  4. That the refrigerant charge is correct

Explanation

A duct leakage test pressurizes or depressurizes the duct system and measures leakage airflow against a specified limit, often expressed as a percentage of system airflow. It verifies installation quality and code or program compliance.

Question 21Planning, Layout, and Estimating

A zone has a sensible load of 36,000 Btu/h and a latent load of 9,000 Btu/h. What is the sensible heat ratio?

  1. 0.75
  2. 0.90
  3. 0.80 Correct answer.
  4. 0.85

Explanation

Sensible heat ratio equals sensible load divided by total load. The total is 45,000 Btu/h, so 36,000 divided by 45,000 equals 0.80.

Question 22Planning, Layout, and Estimating

A furnace rated at 100,000 Btu/h input at sea level is installed at 5,000 ft elevation, where the standard derate is 4% per 1,000 ft above sea level. What input capacity should be expected?

  1. 80,000 Btu/h Correct answer.
  2. 96,000 Btu/h
  3. 84,000 Btu/h
  4. 90,000 Btu/h

Explanation

A 4% derate for each of 5,000 ft gives a 20% reduction in input. Twenty percent of 100,000 Btu/h is 20,000 Btu/h, leaving 80,000 Btu/h.

Question 23Planning, Layout, and Estimating

Manufacturer data show a 3-ton split system loses 3% of its capacity for every 25 ft of equivalent line length beyond the 25 ft base. At 100 ft equivalent length, what capacity remains?

  1. 32,760 Btu/h Correct answer.
  2. 34,920 Btu/h
  3. 33,480 Btu/h
  4. 31,320 Btu/h

Explanation

The length beyond the base is 75 ft, which is three 25-ft increments, so capacity drops 9% from the 36,000 Btu/h nominal rating. Ninety-one percent of 36,000 Btu/h is 32,760 Btu/h.

Question 24Planning, Layout, and Estimating

A system has 0.50 in. w.c. of available static pressure for the supply and return ducts combined. The longest supply path has an effective length of 150 ft and the return path 100 ft. Using the equal-friction method, what friction rate should be used for sizing?

  1. 0.20 in. w.c. per 100 ft Correct answer.
  2. 0.15 in. w.c. per 100 ft
  3. 0.10 in. w.c. per 100 ft
  4. 0.25 in. w.c. per 100 ft

Explanation

The total effective length is 250 ft. Dividing 0.50 in. w.c. by 250 ft gives 0.002 in. w.c. per ft, which equals 0.20 in. w.c. per 100 ft.

Question 25Planning, Layout, and Estimating

A designer replaces a 90-degree square heel takeoff with a 45-degree wye and a curved heel. The primary benefit of that change is which of the following?

  1. Higher velocity in the trunk
  2. Lower pressure loss at the branch Correct answer.
  3. Increased register throw
  4. Reduced need for duct insulation

Explanation

Smooth, gradual branch fittings reduce turbulence and have a lower loss coefficient than abrupt square-heel takeoffs. That lower loss frees static pressure for the rest of the system or allows a smaller fan.

Question 26Planning, Layout, and Estimating

When laying out the location of an outdoor condensing unit on a commercial project, the minimum service and airflow clearances around the unit are established by which source?

  1. The building department's standard plan-check checklist
  2. The architectural site plan showing the equipment pad
  3. The municipal zoning ordinance governing side-yard setbacks
  4. The manufacturer's published installation instructions Correct answer.

Explanation

Mechanical codes require listed equipment to be installed in accordance with its listing and the manufacturer's printed installation instructions, which state the required clearances for service access and air intake/discharge. Zoning setbacks and site plans control where the pad may sit on the lot, but they do not set the clearance envelope around the unit itself.

Question 27Planning, Layout, and Estimating

In HVAC estimating, the quantity survey commonly called the "takeoff" is best described as which of the following?

  1. The schedule of values used for monthly progress billing
  2. The log of change orders issued after the bid was submitted
  3. The summary sheet comparing subcontractors' bid amounts
  4. The itemized measurement of materials and equipment counted from the plans Correct answer.

Explanation

The takeoff is the estimator's systematic count and measurement of every duct, fitting, pipe, fixture, and piece of equipment shown on the drawings, with lengths and quantities extended for pricing. Labor hours and markups are applied to that quantity survey afterward to build the bid.

Question 28Planning, Layout, and Estimating

A horizontal furnace with a draw-through evaporator coil is planned for an attic above a finished ceiling. Which provision is most important for the condensate drainage?

  1. A drain line insulated over its full length
  2. A trapped drain pitched continuously to a safe receptor Correct answer.
  3. A drain line pitched back toward the coil so the trap stays primed
  4. A drain line connected directly to the sanitary sewer without a trap

Explanation

A draw-through coil sits on the negative-pressure side of the blower, so the condensate line needs a trap to prevent air from being pulled in and to allow drainage, and it must slope continuously downhill to a receptor located where leakage or freezing cannot damage the building. Routing it above a finished ceiling makes freeze protection and a safe discharge point especially critical.

Question 29Planning, Layout, and Estimating

While reviewing bid documents, an estimator finds that the mechanical drawings call for a 15-ton packaged unit but the equipment schedule lists a 12.5-ton unit for the same location. What is the appropriate first step?

  1. Submit a request for information to the design engineer before the bid is due Correct answer.
  2. Price the larger unit and include no comment in the bid
  3. Price the smaller unit because schedules always take precedence over plans
  4. Price the average of the two capacities to split the difference

Explanation

Conflicts between drawings and schedules are ambiguities that must be resolved by the designer of record before pricing, typically through a formal request for information or clarification issued during the bid period. Carrying an assumed scope without documentation exposes the contractor to a claim of having included the more expensive item or to a dispute after award.

Question 30Planning, Layout, and Estimating

A packaged rooftop unit is being planned for a new single-story building with steel bar joists. Which information most directly governs the design of the roof curb and the framing at the unit location?

  1. The unit's shipping weight shown on the freight bill
  2. The supply airflow in cfm at design static pressure
  3. The unit's nominal cooling capacity in tons
  4. The unit's operating weight and its point-load reactions Correct answer.

Explanation

Structural support and curb design depend on the operating weight of the unit, including refrigerant charge, accessories, and any factory options, resolved into the concentrated reactions at the unit's points of support. Shipping weight is a transient condition that excludes field-installed components, and capacity or airflow alone say nothing about the load transferred to the structure.

Question 31Ductwork and Sheet Metal Fabrication and Installation

In the equal-friction method of duct sizing, which quantity is held constant throughout the main trunk?

  1. Friction loss per unit length Correct answer.
  2. Total airflow in the trunk
  3. Static pressure at each outlet
  4. Air velocity in each section

Explanation

The equal-friction method sizes each duct section so the friction rate, usually expressed in inches of water gauge per 100 feet, remains the same. Air velocity, static pressure, and airflow change as the duct proceeds and branches take air away.

Question 32Ductwork and Sheet Metal Fabrication and Installation

Which longitudinal seam is most common on rectangular galvanized steel duct?

  1. Standing seam
  2. Pittsburgh lock Correct answer.
  3. Button-punch seam
  4. Lap seam with rivets

Explanation

The Pittsburgh lock is formed on the longitudinal edges of rectangular duct and is folded and locked to create a strong, common seam. It is the standard seam for rectangular galvanized duct in normal pressure classes.

Question 33Ductwork and Sheet Metal Fabrication and Installation

Horizontal rectangular duct is generally supported at intervals not exceeding:

  1. 6 feet
  2. 12 feet
  3. 8 feet
  4. 10 feet Correct answer.

Explanation

Standard duct construction and mechanical code practice limit horizontal rectangular duct supports to 10-foot intervals. Supports must also be placed near fittings and at changes in direction to carry the load properly.

Question 34Ductwork and Sheet Metal Fabrication and Installation

A fire damper is installed where a duct penetrates:

  1. an exterior wall
  2. a rated fire wall assembly Correct answer.
  3. a nonrated interior partition
  4. a corridor ceiling access panel

Explanation

Fire dampers are required at penetrations of fire-rated assemblies to prevent fire from spreading through the duct. The damper must be listed for the application and installed with proper sleeves and access.

Question 35Ductwork and Sheet Metal Fabrication and Installation

The purpose of installing turning vanes in a square duct elbow is to:

  1. reduce turbulence and pressure loss Correct answer.
  2. increase the duct velocity
  3. support the duct liner
  4. provide a balancing adjustment

Explanation

Turning vanes guide the air smoothly around a square elbow, reducing separation and turbulence. This lowers the pressure loss compared with an unvaned square elbow.

Question 36Ductwork and Sheet Metal Fabrication and Installation

As the size of a rectangular duct increases, the required galvanized sheet thickness is obtained by:

  1. changing to aluminum
  2. keeping the same gauge
  3. increasing the gauge number
  4. decreasing the gauge number Correct answer.

Explanation

Sheet metal gauge numbers run opposite to thickness: a smaller gauge number means thicker metal. Larger ducts require heavier metal, so the specified gauge number decreases.

Question 37Ductwork and Sheet Metal Fabrication and Installation

To minimize pressure loss, a flexible duct run should be installed with:

  1. tight 90-degree bends
  2. gentle bends with a generous radius Correct answer.
  3. a slack loop for flexibility
  4. compression at each connection

Explanation

Flexible duct has high friction when bent sharply or compressed. Gentle bends with a radius at least equal to the duct diameter keep resistance low.

Question 38Ductwork and Sheet Metal Fabrication and Installation

SMACNA Seal Class A requires sealing of:

  1. longitudinal seams only
  2. duct penetrations only
  3. all joints, seams, and penetrations Correct answer.
  4. transverse joints only

Explanation

Seal Class A is the most stringent class and requires sealing all transverse joints, longitudinal seams, and duct penetrations. It is used for systems where leakage must be tightly controlled.

Question 39Ductwork and Sheet Metal Fabrication and Installation

A duct run is 150 feet long and is sized at a friction rate of 0.10 in. wg per 100 feet. What is the approximate friction loss?

  1. 1.50 in. wg
  2. 0.25 in. wg
  3. 0.15 in. wg Correct answer.
  4. 0.10 in. wg

Explanation

Friction loss equals the friction rate multiplied by the length divided by 100 feet. Here, 0.10 times 150 divided by 100 gives 0.15 in. wg.

Question 40Ductwork and Sheet Metal Fabrication and Installation

Keeping a rectangular duct's aspect ratio at or below 4:1 primarily:

  1. increases the duct's structural strength
  2. reduces the need for insulation
  3. limits surface area, friction, and installed cost Correct answer.
  4. allows a lighter gauge of metal

Explanation

A high aspect ratio creates a wide, flat duct with more surface area and greater friction for the same airflow. Limiting the ratio to about 4:1 controls surface area, pressure loss, and material cost.

Question 41Ductwork and Sheet Metal Fabrication and Installation

SMACNA recommends that a supply air transition have an included angle no greater than:

  1. 30 degrees
  2. 60 degrees
  3. 15 degrees
  4. 45 degrees Correct answer.

Explanation

A gradual transition limits turbulence and pressure loss; SMACNA generally limits supply air transitions to a 45-degree included angle. Exhaust or high-velocity systems may require an even smaller angle.

Question 42Ductwork and Sheet Metal Fabrication and Installation

Which damper type is preferred for modulating airflow with minimal noise and good control?

  1. Parallel-blade damper
  2. Opposed-blade damper Correct answer.
  3. Barometric damper
  4. Butterfly damper

Explanation

Opposed-blade dampers modulate airflow smoothly because the blades move in opposite directions and keep the air stream more centered. Parallel-blade dampers are better suited to shutoff and two-position control.

Question 43Ductwork and Sheet Metal Fabrication and Installation

SMACNA duct leakage class is expressed in:

  1. cfm per 100 square feet of duct surface Correct answer.
  2. cfm per linear foot of joint
  3. in. wg per 100 feet of duct
  4. percent of total airflow

Explanation

Leakage class is stated as cubic feet per minute of leakage per 100 square feet of duct surface at a specified test pressure. This allows comparison of leakage regardless of duct size.

Question 44Ductwork and Sheet Metal Fabrication and Installation

On a cold-air duct in a humid space, the vapor barrier of the insulation should be installed:

  1. on the inside, next to the metal
  2. on the outside, facing the ambient air Correct answer.
  3. omitted to allow drying
  4. between two layers of insulation

Explanation

The vapor barrier must be on the warm side of the insulation to stop moisture from entering the insulation. For a cold duct, that means the outer jacket facing the humid ambient air.

Question 45Ductwork and Sheet Metal Fabrication and Installation

Compared with a straight tap, a 45-degree angled branch takeoff:

  1. eliminates the need for a volume damper
  2. requires a larger main duct
  3. reduces pressure loss into the branch Correct answer.
  4. increases turbulence at the main

Explanation

An angled takeoff guides air into the branch more gradually, reducing turbulence and pressure loss. A straight tap creates a sharper turn and higher resistance.

Question 46Ductwork and Sheet Metal Fabrication and Installation

Cross-breaking of large rectangular duct panels is done to:

  1. stiffen flat sides and reduce noise Correct answer.
  2. increase the airflow capacity
  3. allow thinner insulation
  4. provide a seal at the seams

Explanation

Cross-breaking adds a shallow bend or crease across large flat panels to increase stiffness. This reduces oil-canning, vibration, and noise in the duct.

Question 47Ductwork and Sheet Metal Fabrication and Installation

A key advantage of spiral round duct over rectangular duct is:

  1. fewer joints and lower leakage Correct answer.
  2. easier concealment in shallow spaces
  3. higher friction loss per foot
  4. lower material cost per pound

Explanation

Spiral duct is made in long sections, so it requires fewer transverse joints than rectangular duct. Fewer joints generally mean lower leakage and faster installation.

Question 48Ductwork and Sheet Metal Fabrication and Installation

A smoke damper is required where a duct penetrates a:

  1. smoke barrier Correct answer.
  2. fire-rated floor assembly
  3. nonrated ceiling
  4. exterior wall

Explanation

Smoke dampers are installed at smoke barriers to prevent smoke from migrating through the duct system. They are listed and controlled to close when smoke is detected.

Question 49Ductwork and Sheet Metal Fabrication and Installation

For proper balancing, a volume damper is best located:

  1. in the middle of the main trunk
  2. at the branch takeoff with access provided Correct answer.
  3. inside the return plenum
  4. at the room diffuser face

Explanation

A volume damper at the branch takeoff adjusts airflow to that branch while affecting the rest of the system as little as possible. Access must be provided so the damper can be adjusted and locked.

Question 50Ductwork and Sheet Metal Fabrication and Installation

Flexible duct should be supported at intervals not exceeding:

  1. 4.5 feet Correct answer.
  2. 8 feet
  3. 10 feet
  4. 6 feet

Explanation

Flexible duct is limited to supports at intervals not exceeding 4.5 feet and within 12 inches of each fitting. This prevents sagging and collapse of the duct's internal liner.