HVAC Excellence Gas Heat Certification study plan

Define complete and incomplete combustion, then write the products of reaction for methane with both sufficient and insufficient primary air.

Calculate the stoichiometric air requirement for natural gas at 1,000 Btu/ft³ and explain how excess air changes the flue CO₂ and O₂ readings.

Distinguish the three legs of the combustion triangle plus the role of ignition energy, and describe what happens to the flame when any leg is reduced.

Explain the difference between ignition temperature, flashback, flame lift, and flame rollout using burner-port velocity and primary aeration.

Identify the Btu content, specific gravity, and Wobbe index significance of natural gas versus propane and explain why orifices are not interchangeable.

Sequence the complete furnace operating cycle from thermostat call to blower off-delay, naming each switch and control that acts at each step.

Trace the gas train from manual shutoff through the gas valve, manifold, and burner, stating the function of each component.

Compare hot-surface, direct-spark, and intermittent-pilot ignition systems and list what each proves before opening the gas valve.

Describe the role of the pressure switch, inducer, limit, and rollout switch in proving safe operation and in lockout.

Explain how a two-stage or modulating gas valve and variable-speed blower change the sequence and airflow profile.

Classify Category I, II, III, and IV venting by pressure and temperature and match each to acceptable vent materials.

Size a natural-draft vent connector and common vent using the tables, including the effects of connector rise, lateral run, and manifold height.

Determine required combustion air by the indoor-air, outdoor-air, and known-infiltration methods, and calculate free area for two-permanent-opening designs.

Explain how a direct-vent, two-pipe system differs from a single-pipe plus indoor-air design, including termination clearances.

Size a gas supply line by load, length, and pressure drop, and identify where a sediment trap, union, and drip leg are required.

Read a furnace wiring diagram and trace the 24 V circuit from transformer through thermostat, pressure switch, and gas valve.

Test a hot-surface igniter and flame sensor with a meter and state pass/fail criteria for each.

Explain flame rectification, why microamps matter, and the effect of a dirty sensor, poor ground, or reversed polarity.

Describe the lockout and retry logic of a modern integrated control board, including blink-code interpretation.

List the safety devices in series in the gas valve circuit and explain what each protects against.

Perform a startup checklist including gas pressure, manifold pressure adjustment, temperature rise, and static pressure measurement.

Adjust manifold pressure for natural gas and propane and explain derating for altitude.

Set airflow to hit the nameplate temperature rise by measuring supply and return temperatures in the correct locations.

Interpret combustion analyzer results for O₂, CO, CO₂, excess air, and stack temperature, and identify acceptable versus unsafe values.

Explain why CO air-free readings and draft measurement must be taken together and how to correct a reading for dilution.

Diagnose no-heat, short-cycling, and lockout complaints by applying the sequence of operation as a decision tree.

Distinguish flame rollout, delayed ignition, and sooting symptoms and identify their likely causes.

Test for spillage and draft at the vent connector and describe the steps to take when spillage is found.

Explain carbon monoxide exposure limits and the procedure for red-tagging an unsafe appliance.

Revisit combustion fundamentals to explain how a cracked heat exchanger, overfiring, or blocked flue raises CO.

Re-sequence the operating cycle from memory and identify the control or switch that fails to advance at each step.

Re-check venting and combustion-air calculations for a tight-construction scenario and justify the upgrade chosen.

Explain how negative building pressure affects draft, spillage, and combustion air in a natural-draft furnace.

Compare common venting, direct venting, and power venting for a replacement installation and state the code-driven constraints.

Take two timed practice exams and score each domain to find weak areas.

Re-study the two lowest-scoring domains and rewrite the cheat sheet and flowchart from memory.

Recite the sequence of operation, combustion targets, and safety limits without notes.

Review all deliverables and fix any calculation or reading you could not justify.