Questions and Answers
What is the heating load for the walls only if the indoor temperature is to be maintained at 60°F?
867,240 btu/hr
What is flash gas?
Answer 4
What load estimating procedure should you use for this building according to code?
How many cfm of total exhaust air will be required for a 10-foot long single island canopy hood?
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How many cubic feet of air is needed for combustion air based on the standard method in a room with a 100,000 btu/hr furnace and two 45,000 btu/hr water heaters?
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How many vibration isolators should be installed in each line when experiencing horizontal and vertical vibration?
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Which of the following options are allowed according to NC Admin Code Title 21, Chapter 50 regarding subcontracting labor?
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The pressure drop for return air grills in residential duct systems is _____?
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What is the heat gain on a residential structure's west-facing wall in Charlotte, NC, with specific construction details?
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An externally equalized thermostatic expansion valve should always be used when the pressure drop across the evaporator coil exceeds ________?
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How many cubic feet of natural gas can a branch line carry in a 20-foot-long EHD18 if the longest length is 90 feet?
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What is the smallest size 2" louver with 45° blades that can bring in 600 cfm of combustion air?
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How many British thermal units does it take to melt 2000 pounds of ice in a 24-hour period?
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The term system operating point refers to the ________?
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What is the winter infiltration rate in cfm for a 4000-square foot, two-story single-family home of average construction?
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What is the cooling cfm required for a light commercial building with a sensible cooling load of 655,900 btu/hr?
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What is an acceptable slope for a converging transition in a commercial duct system?
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Assuming the duct system has 425 feet of equivalent length, what is the design friction rate for a residential air handling unit delivering 1200 cfm at a pressure drop of 0.40?
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What is the least expensive form of protection accepted by code for a clearance of 6-inches to combustible materials for a single-wall pipe?
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When installing plastic gas piping outside and underground, where shall the tracer wire terminate?
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Under what condition can UL listed and labeled Class I flexible air duct pass through a fire-resistance-rated assembly?
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What is the installation requirement for the liner near an electric resistance duct heater?
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When installing sediment traps (drip legs) in gas piping, the length of the sediment trap shall be _________?
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When installing refrigerant suction lines larger than 1 3/8", the insulation on the suction line must be at least ________?
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What is the minimum amount of outside air per minute required for a 3000 square foot seating area in a coffee shop per code?
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What is the heat loss from a residential structure with an R-19 insulated crawlspace and a floor area of 2600 square feet on a design winter day?
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What is the critical temperature of R-410A refrigerant?
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What is the roughness index for fiberglass duct board constructed with good workmanship?
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What must be the velocity of air in an 18" round duct carrying 2400 cfm?
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What is the minimum pipe insulation required for pipes carrying fluids above 105'F and below 55'F?
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What is the approximate pressure drop across a wet 1200 cfm residential evaporator coil?
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What is the manual-D default for excessive length of wire helix flexible duct?
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When running PVC pipe underground for use as part of a domestic kitchen exhaust system, no more than _______ inches of PVC duct is allowed to extend above the concrete floor surface.
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Study Notes
Access Path to Attic Appliances
- Minimum width for continuous solid flooring along access paths to attic appliances is 24 inches according to the 2018 NC Mechanical Code.
Smoke Detectors Installation
- Smoke detectors must be installed according to NFPA 72 when required by code.
Latent Load Calculation
- For 200 machine tool operators, the latent load is 125,000 BTU/hr, calculated as 625 BTU/hr per person.
Heat Loss for an Industrial Assembly
- A building in Asheville, NC with specific insulation and temperature conditions has a heat loss of 19,980 BTU/hr.
Duct Specifications for Commercial Use
- A 24" round spiral duct in a high-class restaurant can handle approximately 4,600 CFM at a maximum velocity of 1500 feet per minute.
CSST Gas Piping System
- For a new gas appliance requiring 45,000 BTU/hr, the minimum CSST size to run with a total length of 80 feet previously established is EHD 23.
Solar Heat Gain in Residential Load
- Minimum solar heat gain coefficient for glass in climate zone 3 of North Carolina is 0.30.
PVC Pipe Venting Regulations
- A maximum of 1 inch of PVC duct can extend above the concrete floor surface when used for a domestic kitchen exhaust system.
Equivalent Round Duct Size
- For a rectangular duct measuring 40" x 34" with insulation, the equivalent round duct size is 35.9".
Gas Piping Considerations
- Sediment traps in gas piping systems must be located after the shutoff valve, as close as possible to the inlet of the equipment.
Duct System Design Friction Rate
- For a residential system delivering 1000 CFM at 0.30 static pressure and 475 feet of equivalent duct length, the design friction rate is 0.063 FR/100'.
Combustion Air Requirements
- A 45,000 BTU/hr hot water heater and a 60,000 BTU/hr furnace require 5,250 cubic feet of combustion air when using indoor air.
Equivalent Length in Duct Fittings
- A 1R fitting has 70 feet more equivalent length compared to a 1Q fitting in a residential duct system.
Heat Gain from Block Walls
- A block wall in Raleigh, NC with specific attributes gains approximately 692 BTU/hr in the summer.
Electric Heaters with Heat Pumps
- The lowest temperature setting for outdoor thermostats controlling electric heaters in heat pumps is 35°F.
Appeal of Code Decisions
- A disagreement with local authority decisions can be appealed to the NC Department of Insurance within 5 days.
Pressure Drop Across Diffusers
- The average total pressure drop across a round commercial diffuser with a neck velocity of 700 feet per minute is 0.75 IWC.
Pressure Drop in Evaporator Coils
- A wet residential evaporator coil has a pressure drop of approximately 0.46 IWC when 1750 CFM of air passes through.
Maximum Face Velocity in Return Air Grills
- The maximum allowable face velocity for return air grills in North Carolina is 450 feet per minute.
Copper Tubing Support Regulations
- The maximum distance between supports for 1/2" semi-rigid copper tubing used as a gas line is 4 feet.
Duct Heater Installation
- The maximum distance a duct heater can be from the air handling unit is 4 feet.
Fire Damper Insulation Requirements
- Insulation must be interrupted by at least 6 inches upstream and downstream of fire dampers installed in duct systems.
Minimum Vapor Compression Efficiency
- The minimum vapor compression efficiency for a 120,000 BTU/hr unit at 17°F outdoor temperature has been set at 2.25.
Licensing for Ductless Units
- Installing an 18,000 BTU/hr ductless unit in a light-commercial building requires an H2 license classification in North Carolina.
Total Sensible Load from Pump Motors
- Ten 20-horsepower pump motors in a pump house produce a total sensible load of 585,000 BTU/hr.
Cooling Factor Calculation
- The cooling factor for a residential HVAC system with a heating load of 34,500 BTU/hr and cooling load of 31,350 BTU/hr is 0.036.
clearance for Gas Venting
- When venting a gas line through an insulated attic, a 1-inch clearance must be maintained with insulation shields.
Permit Validity
- Permits for regulated work in North Carolina are valid for six months, after which they expire.
Heat Loss Calculation for Commercial Walls
- A wall constructed of 8" block with specific finishes in Asheville, NC has a heat loss of approximately 2403 BTU/hr on a design winter day.
Access Requirements for Equipment
- Permanent means of access is required for servicing equipment located 16 feet above grade, even if hidden by a parapet.
HVAC Equipment Selection Procedures
- For one and two-family dwellings and townhouses, HVAC equipment should be selected following ACCA manual-S procedures.
Pipe Insulation Thickness Requirements
- The minimum thickness of pipe insulation on a 3" chilled water supply pipe located inside a building is 1.5 inches.
LP Tank Regulations
- Regulations for LP-tank installations are overseen by the NC Department of Agriculture.
U-Factor Calculation for Added R-Value
- The addition of R-30 insulation that modifies a ceiling's U-factor to 0.018 demonstrates how combined R-values affect thermal performance.
Duct System Design Friction Rate Calculation
- The design friction rate of a duct system, considering a total equivalent length of 480 feet and static pressure of 0.3 IWC, is determined to be 0.062.
Kitchen Exhaust Requirements
- For a 10-foot single island canopied kitchen hood in a commercial setting, a total exhaust air requirement of 5000 CFM is mandated.
Combustion Air Requirements for Large Appliances
- A room with a 100,000 BTU/hr furnace and two 45,000 BTU/hr water heaters needs a total of 9,500 cubic feet of air for combustion.
Vibration Isolators for Compressors
- When installing vibration isolators in lines affected by horizontal and vertical vibration, two isolators are recommended.### HVAC and Refrigeration Principles
- An externally equalized thermostatic expansion valve is necessary when the evaporator coil experiences a pressure drop greater than 25% (answer 2).
- A minimum insulation thickness of 1.5 inches is required for refrigerant suction lines larger than 1 3/8 inches (answer 2).
- The system operating point pertains to duct and blower performance (answer 4).
Airflow and Ductwork Calculations
- A 30" x 10" duct with 1" duct liner requires an airflow velocity of 645 feet per minute to achieve 1000 CFM (answer 2).
- Excessive wire helix flexible duct should have a maximum length adjustment of 0% to 4% according to Manual-D (answer 1).
- The velocity of air in an 18" round duct carrying 2400 CFM is calculated to be 1400 CFM (answer 1).
Load Calculations and Heat Transfer
- A residential west-facing wall in Charlotte experiences a heat gain of 465 BTU/hr during August at 3 PM under default conditions (answer 4).
- Heating load for 33,750 square feet of wall area in a warehouse must reach 867,240 BTU/hr to maintain 60°F indoors (answer 4).
- Heat loss from a 2600-square-foot insulated crawlspace in Charlotte on a design winter day amounts to 1363 BTU/hr (answer 4).
Air Quality and Ventilation
- A coffee shop, serving light food without heavy fryers, does not require a Type I hood for ventilation (answer 2).
- The minimum acceptable outdoor air per minute in a 3000 square feet seating area is 1200 CFM, based on occupant load (answer 1).
Code Compliance and Standards
- Under NC code, a non-binding estimate remains a non-contract after acceptance (answer 2).
- UL-listed and labeled Class I flexible ducts cannot pass through fire-resistant assemblies (answer 3).
- A minimum of 6-inch sediment traps is allowed for gas piping installations (answer 1).
Equipment Specifications
- The maximum outlet air temperature for a furnace in North Carolina is set at 200°F (answer 4).
- The minimum size for an oil supply line feeding an appliance is 3/8" ID tubing (answer 4).
- For an electric resistance duct heater with 1" insulation, the liner must be interrupted 6" before and 6" after the heater (answer 3).
Miscellaneous Topics
- Combustion air requirements for a basement with an 80,000 BTU/hr furnace and a 65,000 BTU/hr water heater total 7200 cubic feet (answer 3).
- In NC, two connected appliances should connect to a single Type B vent using the smaller connector higher in the vent (answer 3).
- The effective pressure drop across a wet 1200 CFM residential evaporator coil is approximately 0.26 IWC (answer 2).
Testing and Inspections
- A final inspection for HVAC systems must occur within 10 days after the system is operational (answer 4).
- When installing plastic gas piping underground, tracer wires must be above grade at both ends (answer 4).
Practical Applications
- For a residential installation with a vibrational issue in refrigerant lines, continuing to isolate the lines from the structure can effectively reduce vibrations (answer 1).
- The typical roughness index for fiberglass duct board with good workmanship is 0.0003 (answer 2).
Refrigerant and Heat Pump Data
- The critical temperature for R-410A refrigerant stands at 72.1°C (answer 4).
- A PTHP heat pump should have a minimum COP of 3.2 for new commercial construction projects (answer 3).
These notes provide a concise summary of important HVAC and refrigeration concepts and code compliance based on the provided text.
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Test your knowledge on residential and light commercial codes based on the NC H3-1 exam sample. This quiz includes questions about minimum requirements and installation guidelines from the 2018 NC mechanical code. Perfect for those preparing for the license exam.
