A technician needs to measure total external static pressure (TESP) on a residential furnace. Where should the two pressure probes be placed?
Service
Question · Medium
Most residential furnace blowers are rated to deliver their nameplate airflow at a total external static pressure no greater than what value?
Question · Easy
Using the standard air formula, what is the air velocity in feet per minute (fpm) when a pitot tube and manometer read a velocity pressure of 0.25 in. w.c.?
Installation
Question · Hard
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A duct traverse with a pitot tube measures an average velocity of 800 fpm in a duct with a cross-sectional area of 2.0 square feet. What is the airflow?
Which instrument directly captures all the air leaving a supply register so the technician can read total CFM at that outlet?
According to the fan laws, if a blower's speed (RPM) is increased by 10%, the airflow (CFM) will change by approximately how much?
Applied Knowledge
A blower's speed is increased by 10%. By approximately how much does the static pressure increase, per the fan laws?
A blower speed is increased by 10%. The required brake horsepower (BHP) will increase by approximately what amount, per the fan laws?
During air balancing, after adjusting dampers the technician must verify that measured total supply and return airflow is within what tolerance of the design airflow?
A homeowner reports one upstairs bedroom is always too warm in cooling. The supply register CFM there is far below the others. What is the most appropriate first corrective action?
In a duct-leakage test, airflow measured through the duct tester when the duct system is pressurized to 25 Pascals is reported as which value?
Which sealing method is NOT acceptable for permanently sealing duct joints and seams?
The conversion 1 PSI equals approximately how many inches of water column (in. w.c.)?
A typical residential cooling system is designed for approximately how much airflow per ton of capacity?
Using the sensible heat formula, what is the sensible Btuh of an air handler delivering 1,000 CFM with a 20F temperature difference between return and supply air?
A gas furnace nameplate specifies a temperature rise range of 40-70F. During service the measured rise is 90F. What does this most likely indicate?
A 'whistling' or high-pitched noise at supply registers when the blower runs is most commonly caused by which condition?
When measuring return-side static pressure on a furnace, the reading on a digital manometer is typically displayed as which type of value?
Which configuration is a common residential supply duct system using a large trunk that stays the same size, with branch runs tapping off it?
System Components
A diffuser's 'throw' specification refers to what?
Which type of damper is installed in a duct that penetrates a fire-rated assembly and closes automatically when heat melts a fusible link?
Per ASHRAE Standard 62.2, the primary purpose of mechanical whole-house ventilation in a residence is to:
Indoor air quality is sometimes evaluated using air changes per hour (ACH). If a 12,000 ft3 space needs 4 air changes per hour, what continuous airflow is required?
A high-efficiency pleated filter (MERV 13) is installed in a system originally sized for a 1-inch fiberglass filter. What airflow problem is most likely?
An anemometer (rotating-vane or hot-wire) measures which property of the airflow?
A blower has a 4-speed PSC motor wired on the medium-low tap, and airflow is below design. Which adjustment most directly increases CFM (assuming static is acceptable)?
An ECM (electronically commutated motor) blower differs from a PSC blower in air distribution because it:
When charting airflow against external static pressure for a blower, the curve that plots CFM versus static pressure is called the:
A return-air duct system is significantly undersized. What is the most likely symptom the technician will measure?
The total external static pressure measured on a furnace is 0.95 in. w.c., well above the 0.50 in. w.c. rating. Component readings show 0.55 in. w.c. across the cooling coil. What is the best conclusion?
Why must a flexible duct be pulled taut and fully extended rather than left compressed or sagging?
Turning vanes are installed in which duct location to reduce turbulence and pressure loss?
A 'Pittsburgh' seam is a type of joint used primarily in which duct material?
Which condition during air balancing would cause a flow hood reading to be artificially LOW on a high-velocity, high-throw diffuser?
When performing proportional air balancing, the technician typically sets which outlet's damper fully open as the reference?
A complete air-balance report should record total pressure, static pressure, and which third pressure reading at measurement points?
Total pressure in a moving air stream is the sum of which two pressures?
A homeowner complains of high utility bills. Inspection finds supply ducts running through a vented attic with torn insulation and unsealed joints. Which problem is the technician most directly addressing by sealing and re-insulating?
For supply ducts located in an unconditioned attic, energy codes (IECC) commonly require a minimum insulation level of about:
A heat recovery ventilator (HRV) improves indoor air quality primarily by:
A 'reducing extended plenum' duct system differs from a plain extended plenum in that it:
Which standard is the primary reference for HVAC duct construction (gauge, reinforcement, sealing) in metal and flexible ductwork?
A technician measures 1,000 CFM total supply and only 700 CFM total return on a system. What does this airflow imbalance most likely indicate?
When sealing the connection of a flexible duct to a sheet-metal collar, the proper sequence is to secure the inner core, then:
A sequencer in an electric-heat air handler controls the heating elements by:
What is the main air-side function of a relay or contactor in an air-distribution system?
A grille selected for a given airflow is chosen primarily on the basis of its:
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