G2 Gas Technician Module 13 2025: Professional Study and Review Guide

How is the heat anticipator setting determined for a thermostat with an adjustable anticipator? • a) By the supply air temperature • b) By measuring the current drawn by the components of the circuit being fed directly by the thermostat • c) By the current rating stamped on the gas valve • d) By the VA rating of the 24-volt control transformer Rationale: The heat anticipator is sized based on the current drawn through the thermostat to prevent overshooting. Other options do not directly affect anticipator sizing. A fan control is a: • a) Normally open temperature control that closes on temperature rise • b) Normally open temperature control that opens on temperature fall • c) Normally closed temperature control that opens on temperature rise • d) Normally closed temperature control that opens on temperature rise Rationale: Fan controls close on temperature rise to start the fan. Other options describe either incorrect switching logic or operation. As the temperature of a thermistor increases, the current flow through it: • a) Increases • b) Decreases • c) Remains the same • d) Fluctuates Rationale: Thermistors used in heating/cooling are typically NTC or PTC. For a PTC thermistor, current increases as temperature rises. A thermostat with a single mercury bulb which controls a single-stage heat, single-stage cool unit is a: • a) SPST (single pole single throw) • b) SPDT (single pole double throw) • c) DPST (double pole single throw) • d) DPDT (double pole double throw) Rationale: SPDT thermostats switch between heating and cooling using one pole and two throws. SPST and DP types are for simpler or more complex circuits. A thermostat serving a unit with separate heating and cooling control transformers and one stage of heating and cooling is a: • a) SPST • b) SPDT • c) DPST • d) DPDT Rationale: DPDT is used when separate transformers are present, providing double-pole double-throw switching for independent heating and cooling circuits. Which of the following heating systems would be expected to cause problems due to the “distribution effect”? • a) A direct vent furnace • b) A conventional vent type boiler • c) A forced air furnace with no return air openings in the furnace room • d) A forced air furnace with a return air opening in the furnace room Rationale: Proper return air can create distribution issues if airflow is unbalanced. Other systems are less affected by the distribution effect. The recommended range of relative humidity in a house to control indoor air contaminants and maintain comfort is: • a) 0% to 20% • b) 30% to 50% • c) 60% to 80% • d) 90% to 100% Rationale: 30–50% RH reduces mold growth and maintains comfort. Lower or higher RH can cause discomfort or material damage. Which action will have the greatest effect on reducing mold growth in a house? • a) Reducing RH to ~10% • b) Increasing RH to ~80% • c) Filtering the air in the house • d) Covering earthen floors and open water surfaces (sumps, aquariums, etc.) Rationale: Controlling moisture sources is most effective in preventing mold. Filtering or RH adjustment alone does not remove the source of mold. After a direct vent radiant heating system is installed and walls/windows are wet, the most reasonable response is: • a) Advise customer to call somebody else • b) Recommend leaving a window open • c) Advise it will disappear as the building dries • d) Recommend the installation of a mechanical ventilation system Rationale: Moisture accumulation is best addressed via proper ventilation. Other options do not solve the root cause. The most common cause of flue gas spillage from gas appliances is: • a) Positive air pressure caused by mechanical systems • b) Negative air pressure caused by mechanical systems • c) Cracked or leaking heat exchangers • d) Chimneys which are too short Rationale: Negative pressure can pull combustion gases back into the living space. Other options are less common causes. There are two appliances in a 10 ft × 10 ft × 20 ft structure with an equivalent leakage area greater than 0.05 m². A furnace has a draft hood and an input of 50,000 Btuh. The second appliance has an input of 75,000 Btuh and does not have a draft hood. The required combustion air opening size is: • a) 0 square inches (0 mm²) • b) 7 square inches (4500 mm²) • c) 9 square inches (5800 mm²) • d) 1 square inch (7000 mm²) Rationale: Combustion air is required for appliances without a draft hood; proper sizing ensures safe combustion. Other options are either too small or too large. Air enters a house through a process called: • a) Infiltration • b) Exfiltration • c) Aspiration • d) Expiration Rationale: Infiltration refers to air entering through leaks in the building envelope. Exfiltration is air leaving the house, and the other terms are unrelated.