NATE Gas Heating Service study plan

Define the three legs of the combustion triangle and explain what happens to flame shape and CO output when each leg is starved.

Calculate stoichiometric air required for natural gas and propane using their respective heating values and air-fuel ratios, and compute percent excess air from a measured CO2 or O2 reading.

Convert between Btu, therms, and cubic feet of gas, and compute input rate from a timed meter clocking at a given manifold pressure.

Distinguish complete from incomplete combustion by interpreting flame color, lift, flashback, and yellow tipping, and state the cause of each.

Explain dew point of flue products and why condensing versus non-condensing appliances tolerate different stack temperatures.

Classify venting categories I through IV by pressure and temperature and match each to appliance types and approved vent materials.

Size a Category I natural-draft vent connector and chimney using the appliance input, connector rise, and height, and identify when a common vent is prohibited.

Compute required combustion air for a confined space using the two-permanent-opening method and the known-air-infiltration method, and state when a confined space becomes unconfined.

Explain the difference between spillage, backdrafting, and blocked-flue conditions, and list the test steps and instruments used to detect each.

Identify code requirements for termination clearances, vent slope, and condensation drainage on condensing appliances.

Trace the gas path from meter to burner, naming every safety and control device in order and stating each device's function.

Size a gas supply line using the longest-run method and the appropriate capacity table for the fuel's specific gravity and pressure drop.

Explain the operation of a redundant combination gas valve, including the regulator, safety shutoff, and operator sections, and describe the manifold pressure adjustment procedure.

Identify burner components - orifice, manifold, spuds, primary and secondary air shutters - and describe the symptom of a mis-sized or clogged orifice.

Perform and document a leak test on new piping and describe the pressure and duration requirements for the test.

Describe the ignition sequence of a hot-surface and a spark-to-pilot system, listing the safety timing windows (pre-purge, trial for ignition, flame-establishing period, post-purge) and what happens on failure at each step.

Explain flame rectification, including why the flame sensor needs a clean surface, why polarity and grounding matter, and how to measure microamp signal.

Read a ladder diagram and a manufacturer wiring schematic and trace the call for heat through the safety chain to the gas valve.

Test the limits of a rollout switch, high-limit, pressure switch, and flame rollout circuit, and explain how each interrupts the safety chain.

Demonstrate safe electrical troubleshooting practice: lockout/tagout, meter usage, and verifying 24 V control versus line voltage.

Measure static pressure across the air handler and in the supply and return plenums, and compute total external static pressure.

Calculate temperature rise from supply and return temperatures and compare it to the data plate range, then determine whether airflow must be increased or decreased.

Interpret a blower performance table to select the correct speed tap for a target CFM at a measured static pressure.

Explain how a restricted heat exchanger or dirty evaporator coil changes temperature rise and what combustion symptoms accompany it.

Perform a combustion analysis with an electronic analyzer: zero and calibrate the instrument, sample before and after the heat exchanger, and record O2, CO, CO2, stack temperature, and draft.

Calculate steady-state efficiency and excess air from analyzer readings, and interpret CO air-free versus as-measured values.

Diagnose five common faults from symptoms alone: delayed ignition, flame rollout, short cycling, pilot outage, and high CO with normal draft.

Verify draft in the vent connector and at the appliance outlet and determine whether a draft reading indicates spillage or an over-draft condition.

Write a customer-facing explanation of combustion test results that avoids jargon while remaining accurate.

Build a troubleshooting decision tree for 'no heat' that branches on thermostat call, induced-draft proving, ignition attempt, flame sensing, and gas valve operation.

Practice meter-based diagnosis of a pressure switch that will not close and a flame sensor reading below the manufacturer's minimum microamp threshold.

Verify manifold pressure and gas input on a running appliance and identify the adjustment and measurement points on a combination valve.

Describe the correct procedure for replacing a gas valve, including leak testing, clocking the meter afterward, and combustion re-verification.

List the documentation required after a repair: combustion readings, leak test, temperature rise, and any de-rating for altitude.

Complete a timed 100-question practice set weighted by domain percentage and score each domain separately to identify remaining weak areas.

Re-study the two lowest-scoring domains using the week 1–7 deliverables as reference notes.

Recite from memory the key code limits: combustion air volumes, vent termination clearances, pipe sizing pressure drop, and temperature rise tolerance.

Rehearse the combustion analysis and static pressure procedures end to end without notes to confirm procedural fluency.