Pre-Startup Safety & JHA (Job Hazard Analysis)
Perform a JHA before you touch the appliance. Confirm site access, lighting, ladder safety, and clear work zones. Lock out/tag out the disconnect and gas cock; verify with a non-contact tester and a manometer reading of zero downstream. Check clearances to combustibles against the nameplate and local code. Confirm ventilation adequacy for both combustion and technician safety—especially in tight mechanical rooms or crawlspaces. PPE: safety glasses, cut-resistant/insulated gloves, steel-toe boots, and respiratory protection if dust or combustion byproducts are present.
If the existing furnace is being replaced, stage filters, traps, and gaskets from Accessories to avoid mid-startup delays.
Pre-Installation Verification & Receiving Inspection
Match the installed model/serial to the work order. Inspect cabinet, heat exchanger access panels, and shipping blocks. Verify orientation (upflow/downflow/horizontal) matches duct geometry. Confirm filter rack and new filter are present and properly sized; record the MERV rating. Check that the condensate kit (if 90%+) is complete and correctly trapped. Ensure electrical feed, circuit size, and overcurrent protection align with nameplate voltage/FLA.
Visual:
Electrical Feed → Disconnect → Furnace L1/L2
Gas Meter → Regulator → Shutoff → Drip Leg → Gas Valve → Manifold
Document all findings on your startup form. Correct minor issues now; note anything deferred for owner approval.
Where to get parts: gaskets, traps, line sets, pads, and more in Accessories.
Visual & Physical Inspection (Steps 1–6)
Open the burner compartment. Clean burners, crossover ports, and the burner box—no scale, lint, or insect debris. Verify grounding and screw-tight wire terminations; look for heat-stressed insulation. Inspect the heat exchanger with a bright light and mirror; any suspected crack or rust-through is a red tag until resolved. Clean and test the flame sensor (light scuff only) and verify ignitor resistance against manufacturer spec.
Visual – Heat Exchanger/Flame Path:
Return → Blower → Heat Exchanger → Burners/Flame → Supply
Replace or document filter condition (record size and MERV). Confirm door switch operation and gasket integrity. Tighten neutral/ground bonds.
Record baseline micro-amp flame signal after ignition; trend it yearly in your maintenance log. For replacement filters and media cabinets, see Accessories.
Mechanical Components Assessment (Steps 7–13)
Remove and clean the blower wheel; impacted dust can slash airflow and raise temperature rise. Spin the motor; check for rough bearings. Test the run capacitor under load replace it with outside tolerance. Verify set screws on wheel/shaft and fan orientation. Check manual and automatic dampers; position for the heating season. Inspect and flush condensate drains; confirm proper trap height and slope to an approved termination.
Visual – Condensate Trap:
HX Drain → P-Trap (min. 2" water seal) → Slope 1/8" per ft → Condensate Pump/Drain
Lubricate moving parts if the OEM allows it (many ECM/SEALED motors do not). Inspect isolation rails and cabinet fasteners to reduce vibration.
After cleaning, measure total external static pressure (TESP) to confirm the blower is actually delivering the expected CFM. If not, correct duct restrictions before calling the furnace “ready.”
Venting & Combustion Air Verification
For 80% units, verify vent connector rise, minimal horizontal runs, and continuous positive slope to the chimney/vent. For 90%+ PVC/CPVC/PP systems, confirm slope back to the furnace for condensate return, glue type, and hangers per spec. Check terminations for separation, height, and clearance to openings.
Visual – Vent Slope:
Furnace →====(¼" per foot back to furnace)====→ Termination
Confirm adequate combustion air: dedicated ducts/intakes per manual or code equations for confined spaces. Inspect intake screens for debris. Verify clearances to combustibles around the vent and at roof/wall penetrations.
If local wind conditions cause nuisance trips, consider factory-approved termination kits or wind hoods. Replacement vent kits and sealants are stocked under Accessories.
Gas System Pressures & Leak Testing
Attach a calibrated manometer. Verify inlet (supply) pressure: Natural Gas ≥ 5" WC (never above ~10.5"), LP ≥ 11" WC (never above ~13"). Set manifold pressure to the OEM range: NG typically 3.2–3.8" WC; LP 10–11" WC. Adjust using the gas valve regulator screw with burners firing at steady state.
Perform leak checks at every threaded/appliance joint using approved leak solution or an electronic detector. Verify drip leg and union placement.
Side note – Manometer hook-up:
Supply test port = inlet; valve outlet port = manifold. Cap ports after testing.
If you’re planning a system changeout, explore Design Center support.
Electrical Safety & Performance Checks
Confirm supply voltage within OEM tolerance and correct polarity/hot-neutral orientation. Verify equipment ground continuity. Check breaker/fuse sizing versus nameplate MCA/MOP. Inspect the control board for discoloration, bulged components, or loose standoffs. Measure motor amperage at high heat tap and compare to motor FLA; excessive draw points to airflow issues or failing bearings.
Quick Map:
L1/L2 → Transformer → Board → Inducer → Ignition → Gas Valve → Blower
Confirm low-voltage wiring integrity (stat cable, splices, and C-wire continuity). Tighten all lugs o torque spec if provided.
Log voltage sag during ignition sequence; poor utility or undersized conductors can drop the inducer/ignitor and cause lockouts. For smart stat integrations, see our Help Center.
Operational Testing & Temperature Rise
With the cabinet closed and filter installed, initiate a heat call. Verify ignition timing, flame carryover, and steady blue flame without lifting or rollout. Confirm inducer and pressure switch sequence. Measure temperature rise between return and supply downstream of the heat exchanger; adjust blower speed to keep rise within the nameplate window.
Visual – Temp Rise Points:
Return Probe →[HX]→ Supply Probe (post-mixing, before first branch)
Simulate a power loss and gas interruption; confirm safe shutdown and clean relight.: Use TESP and temperature rise together to back-calculate approximate airflow. If rise is high and TESP is high, the restriction is real—often filter, coil face, or undersized return.
Carbon Monoxide Testing & Combustion Analysis
Use a combustion analyzer after at least 10 minutes of steady operation. Measure CO and O₂/CO₂ in the flue, plus ambient CO in the mechanical space and supply air. Surrounding air should not exceed 10 ppm CO; any elevated reading demands immediate correction. Verify draft (for non-condensing) and confirm no flue spillage at startup.
Visual – Test Points:
Flue Sample Port • Room Air (free air) • Supply Plenum (circulating air)
If CO is high, inspect for blocked heat exchanger passages, incorrect gas pressure, poor primary air, or recirculation via a leaky vent or return. Document analyzer make/model, calibration date, and all readings on the commissioning sheet.
On modulating/multistage furnaces, record readings at each firing rate; some issues only present at low fire.
Commissioning Docs, Warranty Protection & Owner Handoff
Complete a commissioning checklist: model/serials, gas pressures (inlet/manifold), TESP, airflow verification (within ±15% of design), temperature rise, electrical readings, CO/combustion data, and control settings. Keep records ≥ 3 years. Many warranties require proof of professional commissioning and compliance with manufacturer procedures—missing paperwork can void coverage.
Provide the owner with filter sizes, replacement intervals, and a simple operating guide. Label the furnace with your baseline readings and the commissioning date. Discuss financing/options if the system needs upgrades or accessories via HVAC Financing.
