The article explains gas furnace amp draw, including typical amp usage for blowers, ignitors, and control boards, how to measure amps safely, and tips to reduce electrical load. It helps homeowners and technicians understand how many amps a gas furnace uses and interpret those readings for troubleshooting and efficiency improvements.
| Component | Typical Amp Draw (Amps) | Notes |
|---|---|---|
| Inducer Motor | 1–3 A | Runs during draft cycle and ignition |
| Blower Motor (PSC) | 3–8 A | Depends on speed and motor type |
| Blower Motor (ECM/Variable) | 1–6 A | Lower at low speeds, higher at high speeds |
| Ignitor/Hot Surface | 2–10 A (surge) | High inrush during ignition for short duration |
| Control Board/Relay | <1 A | Steady low power draw |
| Total Typical System | 3–12 A | Varies by model, size, and accessory loads |
Content Navigation
- Why Amp Draw Matters For Gas Furnaces
- Key Electrical Components And Their Amp Draw
- How To Measure Gas Furnace Amp Draw Safely
- Interpreting Amp Readings: Normal Versus Problem Signs
- Common Causes Of Excessive Amp Draw And Fixes
- Electrical Circuit Considerations And Breaker Sizing
- Energy Efficiency And Amp Draw: ECM Versus PSC Motors
- How Amp Draw Affects Utility Costs And Performance
- Troubleshooting Checklist For High Or Low Amp Readings
- When To Call A Professional
- Recordkeeping And Maintenance Best Practices
- Additional Resources And Tools
Why Amp Draw Matters For Gas Furnaces
Understanding gas furnace amp draw is essential for diagnosing electrical problems, ensuring circuits are not overloaded, and verifying that components operate within manufacturer specifications.
Accurate amp readings can prevent nuisance tripping of breakers, reduce fire risk, and extend furnace lifespan by catching failing motors or shorted components early.
Key Electrical Components And Their Amp Draw
Blower Motor
The blower motor moves heated air through the ductwork and is typically the largest continuous electrical load. Blower amp draw varies by motor type: PSC (permanent split capacitor) motors draw more current at equivalent airflow than modern ECM (electronically commutated) motors.
PSC motors often draw 3–8 amps on single-phase 120V systems for residential furnaces, while ECM motors can range from 1–6 amps depending on speed and load due to higher efficiency and variable-speed operation.
Inducer Motor
The inducer motor ensures proper venting and assists with combustion air flow. It typically runs during the heating cycle except when the blower operates at low-speed cooling modes. Inducer motors usually draw between 1 and 3 amps on 120V circuits.
Ignitor And Ignition Controls
Modern hot surface ignitors briefly draw significant current during warm-up, and spark igniters draw in short bursts. Hot surface ignitors can show an inrush that appears higher on meters but last only a few seconds. Typical readings can be 2–10 amps transiently, depending on design.
Control Board, Thermostat, And Accessories
The control board and thermostat draw minimal continuous current, typically under 1 amp. Accessories such as humidifiers, electronic air cleaners, or zone dampers add to total amp draw and should be included in circuit calculations.
How To Measure Gas Furnace Amp Draw Safely
Measuring amp draw requires a clamp meter or ammeter and adherence to safety protocols. Always follow manufacturer guidelines and local electrical codes. If unsure, hire a qualified HVAC electrician or technician.
- Turn off power at the furnace switch and the breaker before opening panels.
- Access motor wiring where the conductors are exposed or at the control terminals.
- Use a clamp meter around a single conductor, not the entire cable with both hot and neutral, to get an accurate reading.
- Record readings during relevant stages: inducer start, ignition, blower on low/medium/high, and steady state heating.
- Compare readings to nameplate values and manufacturer specs.
Interpreting Amp Readings: Normal Versus Problem Signs
Normal amp draw values vary by model and motor type. Use the furnace nameplate and installation manual as the primary reference. Unexpected readings can indicate issues such as worn bearings, failing capacitors, electrical short, or mechanical blockage.
- High Continuous Amps: May indicate motor strain due to dirty blower wheel, failing bearings, or incorrect blower speed settings.
- High Inrush Only: Typical for ignitors and motors at startup but should settle quickly.
- Fluctuating or Intermittent Readings: Could signify capacitor issues, loose wiring, or failing motor windings.
- Near Zero Amps: Suggests an open circuit, blown fuse, or failed component that is not receiving power.
Common Causes Of Excessive Amp Draw And Fixes
Dirty Blower Wheel Or Filter
A clogged filter or debris on the blower wheel increases static pressure and motor load. Cleaning or replacing the filter and cleaning the blower wheel typically restores normal amp draw.
Worn Motor Bearings Or Windings
Worn bearings or deteriorating motor windings cause increased friction and electrical resistance, raising amp draw. Replacing the motor is the usual remedy; some motors are not serviceable.
Incorrect Motor Speed/Tap Setting
PSC motors have discrete speed taps. If incorrectly set to a high-speed tap for a fixed blower curve, the motor may draw more current than needed. Verify tap settings per manufacturer documentation.
Failing Capacitor (For PSC Motors)
A weak start/run capacitor increases motor current and reduces torque. Testing and replacing the capacitor often resolves elevated amp draw for starting or running issues.
Electrical Circuit Considerations And Breaker Sizing
Furnaces are typically wired to a dedicated 120V or 240V circuit depending on model and accessories. The National Electrical Code recommends continuous loads not exceed 80% of the circuit rating.
For a 120V circuit on a 15A breaker, the safe continuous amp limit is 12 amps. If the furnace and accessories draw near this value, consider a 20A circuit or dividing loads as appropriate.
Energy Efficiency And Amp Draw: ECM Versus PSC Motors
ECM motors improve energy efficiency by varying speed to match demand and often draw less average current than PSC motors for equivalent airflow. ECM-driven systems can lower electrical consumption and reduce peak amp draw during heating cycles.
Upgrading to an ECM blower motor can be a cost-effective efficiency measure, but initial equipment compatibility and control wiring should be evaluated by an HVAC professional.
How Amp Draw Affects Utility Costs And Performance
Electrical consumption from a gas furnace is modest compared to fuel use, but amp draw impacts electricity bills and system reliability. Lower amp draw reduces run-time electrical costs and decreases the likelihood of tripped breakers.
Monitoring amp draw can also reveal performance degradation before it causes a full component failure, allowing for planned maintenance and reduced emergency repair costs.
Troubleshooting Checklist For High Or Low Amp Readings
- Verify correct measurement technique and tool calibration.
- Inspect and replace dirty air filters and clean blower components.
- Check blower wheel alignment and motor mounting for mechanical binding.
- Test capacitors and replace if outside tolerance.
- Measure voltage at the motor to confirm proper supply; low voltage can cause higher current draw.
- Inspect wiring and terminals for corrosion, loose connections, or shorted insulation.
- Compare readings to nameplate and consult manufacturer error codes for related symptoms.
When To Call A Professional
If amp draw readings are outside expected ranges despite simple fixes like filters and cleaning, a licensed HVAC technician should evaluate motors, control boards, and electrical components. Handling live electrical components carries risk and may require specialized tools and expertise.
Professional evaluation is also recommended when considering motor upgrades, circuit modifications, or if the furnace is tripping breakers repeatedly.
Recordkeeping And Maintenance Best Practices
Keeping a log of amp readings over time helps track degradation and the impact of repairs. Record readings for inducer start, ignition, and blower at multiple speeds after maintenance or seasonal startup.
Regular preventive maintenance, including filter replacement, duct cleaning, and annual tune-ups, maintains optimal amp draw and system reliability.
Tips for Getting the Best HVAC Prices
- Prioritize Quality Over Cost
The most critical factor in any HVAC project is the quality of the installation. Don’t compromise on contractor expertise just to save money. - Check for Rebates
Always research current rebates and incentives — they can significantly reduce your overall cost. - Compare Multiple Quotes
Request at least three estimates before making your choice. You can click here to get three free quotes from local professionals. These quotes include available rebates and tax credits and automatically exclude unqualified contractors. - Negotiate Smartly
Once you've chosen a contractor, use the proven strategies from our guide — How Homeowners Can Negotiate with HVAC Dealers — to get the best possible final price.
Additional Resources And Tools
- Clamp meters with True RMS capability for accurate AC measurements.
- Manufacturer technical manuals and nameplate data for amp and voltage specifications.
- HVAC technician training guides and electrical code references (NEC).
- Online diagnostic forums and OEM support for model-specific troubleshooting.