How Many Amps Does a Gas Furnace Draw: Typical Loads and What to Expect

How Many Amps Does A Gas Furnace Draw is a common question for homeowners planning electrical capacity, troubleshooting tripped breakers, or sizing a generator. This article explains typical amp draws for gas furnace components, differences between motor types, how to measure current, and practical guidance for circuit sizing and troubleshooting.

Component	Typical Running Amps	Typical Starting/Peak Amps
Blower Motor (PSC)	3–10 A	6–30 A
Blower Motor (ECM/Variable)	0.5–6 A	1–10 A
Inducer Motor	1–4 A	2–8 A
Hot Surface Ignitor	2–3 A (when active)	2–3 A
Spark Igniter / Control Board	<1 A	<1 A
Gas Valve	0.2–1.5 A	0.2–1.5 A

How Gas Furnaces Use Electricity

Although a gas furnace burns natural gas to produce heat, it still depends on electricity for fans, controls, ignition, and safety systems. These electrical components determine how many amps a gas furnace draws from the house electrical system during each stage of operation.

Key electrical stages include thermostat call, inducer motor start, ignition sequence, burner operation, and blower fan run. Each stage has a distinct current draw profile that affects overall circuit demand.

Typical Amp Draw By Component

Blower Motor (Air Handler/Blower)

The blower motor is usually the largest electrical load in a gas furnace. There are two main motor types: PSC (permanent split capacitor) and ECM (electronically commutated motor).

• PSC motors commonly run between 3 and 10 amps, with startup (inrush) currents that can be several times the running amps, sometimes reaching 6–30 amps briefly.
• ECM motors are more efficient and variable-speed, typically running between 0.5 and 6 amps. ECM inrush is much lower, often 1–10 amps.

Inducer Motor

The inducer motor powers the draft fan that clears combustion gases before ignition. Inducer motors often draw 1–4 amps during operation. Startup may briefly double that value for heavy-duty units.

Ignitor Types: Hot Surface vs Spark

Hot surface ignitors (HSI) draw noticeable current—commonly 2–3 amps while heating the ceramic element. Spark ignitors draw much less current; the control board and transformer supplying the spark use under 1 amp total.

Gas Valve and Control Board

Gas valves typically draw between 0.2 and 1.5 amps depending on design. The control board and low-voltage transformer for the thermostat usually consume under 1 amp combined.

Overall Furnace Amp Draw: Typical Ranges

Most single-stage residential gas furnaces on a 120-volt circuit draw between 5 and 15 amps during normal operation, depending on blower motor type and speed.

High-efficiency or variable-speed furnaces with ECM blowers often draw 2–8 amps in normal heating. Older PSC systems or systems with larger blowers can draw 8–15 amps or briefly more during startup.

Some air handlers or large furnaces use 240 volts for the blower; those systems will show lower amp numbers on each hot leg but still require appropriately sized breakers, often 10–20 amps depending on motor power.

Why Startup (Inrush) Current Matters

Electric motors draw more current on startup than while running. Inrush current can be 3–6 times the running current for PSC motors. Circuit breakers are designed to tolerate short surges, but repeated high inrush or a weak breaker can cause nuisance trips.

ECM motors have lower inrush, which often prevents nuisance trips and reduces peak electrical demand.

How To Measure Furnace Amps Safely

1. Use A Clamp Meter: Place the clamp around a single conductor (hot lead) while furnace is running to read amps without disconnecting wires.
2. Measure Each Component Stage: Record amps for inducer, ignitor, and blower individually by observing during their active intervals.
3. Ensure Safety: Turn off power before installing or removing measurement devices. Follow manufacturer instructions and wear appropriate safety gear.

Recommended Measurement Steps

Start by measuring the blower motor while the furnace blower is running. Next, measure the inducer during startup and the ignitor during its heating period. For total load, measure at the furnace’s main supply conductor.

Circuit Sizing And Breaker Considerations

Furnaces are typically connected to a dedicated 120V or 240V circuit. National Electrical Code (NEC) requires continuous loads be calculated at 125% for circuit rating.

• A furnace drawing 12 amps continuously should be on a circuit rated for at least 15 amps (12A × 125% = 15A) and more commonly a 20A breaker is used for margin.
• For systems with higher startup current or combined loads (e.g., furnace plus humidifier), a 20-amp or larger dedicated circuit may be required.

Always consult local code and a licensed electrician for final circuit selection and breaker sizing.

Common Problems Indicated By Abnormal Amps

High Running Amps can indicate mechanical resistance, failing bearings, blocked airflow, or an overworked blower motor. Persistent high amps shorten motor life and may trip breakers.

Low Running Amps on a PSC motor can signal capacitor failure or motor winding issues. On ECM motors, unusually low current during operation could mean motor control issues or the motor running at a low commanded speed.

Frequent Breaker Trips typically point to undervalued breakers, high inrush with older motors, or an overloaded circuit shared with other appliances.

Upgrading To Improve Electrical Performance

Switching to an ECM blower can reduce typical running amps and inrush, improving efficiency and reducing electrical stress. Variable-speed blowers better match airflow needs and often lower energy use.

Other upgrades include installing a soft-start device for PSC motors, ensuring proper capacitor sizing, and fixing duct restrictions to reduce motor load.

Generator Sizing And Portable Power Considerations

When connecting a gas furnace to a portable generator, consider both running and starting amps. For older PSC motors, choose a generator with enough surge capacity to handle 3–6× the motor’s running amps for a few seconds.

Example: A furnace with a 10A blower (running) and 30A inrush would typically need a generator that can supply a surge of at least 30A on the same voltage leg. A conservative selection often places the generator capacity at 2000–3500 watts for smaller furnaces and larger for high-efficiency systems with multiple motors.

Practical Examples And Typical Systems

Furnace Type	Voltage	Typical Running Amps	Recommended Breaker
Older Single-Stage, PSC Blower	120V	8–15 A	20 A
High-Efficiency Furnace With ECM	120V	2–8 A	15–20 A
Furnace With 240V Blower Motor	240V	5–12 A (per leg)	15–20 A

Best Practices For Homeowners

• Document measured amp values for normal operation to compare during troubleshooting.
• Schedule periodic HVAC maintenance to prevent airflow restrictions and motor strain.
• Use a dedicated circuit for the furnace to avoid shared-load problems.
• Consult a licensed HVAC technician or electrician if furnace amps are outside typical ranges.

Frequently Asked Questions

Can A Furnace Trip A 15-Amp Breaker?

Yes. A furnace with a high inrush PSC motor or combined loads on the same circuit can trip a 15-amp breaker. Many installers use a 20-amp dedicated circuit to avoid nuisance trips.

Does A High-Efficiency Furnace Draw Less Electricity?

Generally yes. High-efficiency furnaces with ECM blowers draw less electrical current and have lower inrush, reducing electricity use and decreasing the chance of tripping breakers.

Is It Normal For The Ignitor To Use 2–3 Amps?

Yes. Hot surface ignitors draw a few amps while heating. The draw is temporary and occurs only during the ignition sequence.

When To Call A Professional

If amp readings are consistently outside the typical ranges, breakers trip repeatedly, or the blower sounds strained, a licensed HVAC technician or electrician should inspect the system. Professionals can measure amps accurately, test capacitors and motor windings, and ensure safe, code-compliant electrical connections.

For Accurate Assessment, homeowners should provide technicians with measurements taken with a clamp meter and describe when trips or abnormalities occur to speed diagnosis.