Most homeowners worry about high winter energy bills. You might think your gas furnace only burns natural gas. But here’s the truth: it also uses electricity to run key components. Understanding how many watts does a gas furnace use helps you plan for power outages, choose the right backup generator, and manage your monthly costs better.
This guide breaks down gas furnace electricity usage in simple terms. You’ll learn exact wattage numbers, what affects power consumption, and how to calculate your actual costs.
How Many Watts Does a Gas Furnace Use on Average
A typical gas furnace uses between 400 and 1,200 watts of electricity during operation. Most residential models fall in the 600-800 watt range. This might surprise you since gas furnaces get their heating power from natural gas or propane.
The electrical components handle critical functions. Your blower motor uses the most power, drawing 300-750 watts depending on the motor type. The electronic ignition system needs 80-120 watts to light the burners. The control board and transformer use another 50-100 watts combined.
Here’s a breakdown of gas furnace power consumption by component:
| Component | Wattage Range | Function |
| Blower Motor | 300-750 watts | Circulates warm air through home |
| Ignition System | 80-120 watts | Lights gas burners |
| Control Board | 20-50 watts | Manages heating sequence |
| Draft Inducer | 50-100 watts | Vents exhaust gases safely |
| Transformer | 10-20 watts | Powers thermostat circuit |
Starting wattage differs from running wattage. When your furnace kicks on, it briefly draws 1.5 to 2 times its normal operating wattage. A furnace that uses 600 watts during normal operation might spike to 900-1,200 watts for a few seconds. This matters when sizing backup generators.
Variable-speed ECM (electronically commutated motor) blowers use less power than older single-speed motors. These newer motors adjust speed based on heating demand, saving energy and money.
At Milehi Hvac, we see many homeowners surprised by their furnace’s electrical needs. Our furnace installation services in Denver include detailed power consumption analysis to help you choose the most efficient system for your home.
Gas Furnace Wattage by Size and BTU Rating
Your furnace size directly affects gas furnace electricity usage. Larger heating capacity means bigger blowers and more electrical draw.
| Furnace Size (BTU) | Typical Wattage | Best For |
| 40,000-60,000 BTU | 400-600 watts | Homes under 1,500 sq ft |
| 60,000-100,000 BTU | 600-900 watts | Homes 1,500-2,500 sq ft |
| 100,000-150,000 BTU | 900-1,200 watts | Homes over 2,500 sq ft |
The AFUE rating (Annual Fuel Utilization Efficiency) affects electrical components too. High-efficiency furnaces above 90% AFUE often use variable-speed blowers that reduce electricity consumption by 30-50% compared to standard models.
Average Wattage by Furnace Type
Comparing different heating systems shows why gas furnaces are energy-smart.
| Heating System | Wattage Range | Energy Source |
| Gas Furnace | 400-1,200 watts | Natural gas + electricity |
| Electric Furnace | 10,000-50,000 watts | Electricity only |
| Oil Furnace | 800-1,400 watts | Heating oil + electricity |
| Heat Pump | 3,000-5,000 watts | Electricity only |
| Propane Furnace | 400-1,200 watts | Propane + electricity |
Gas furnaces offer the best balance. They use 400-1,200 watts of electricity while natural gas provides the actual heat. The gas furnace wattage stays relatively low because electricity only powers auxiliary systems.
Electric furnaces are power-hungry. They consume 10,000-50,000 watts because electricity generates all the heat. A typical 15,000-watt electric furnace costs significantly more to operate than a comparable gas unit.
You may read How Long Does A Gas Furnace Last?
Factors Affecting Wattage
Several variables change how much electricity your gas furnace actually uses.
Blower Motor Technology: Old PSC (permanent split capacitor) motors from furnaces built before 2000 draw 500-800 watts continuously. Modern ECM variable-speed motors use 200-600 watts and adjust based on demand. Upgrading to an ECM motor can cut your furnace’s electrical costs in half.
Home Size and Insulation: Poorly insulated homes make furnaces run longer. Leaky ductwork wastes heated air, forcing your blower to work harder. Both situations increase daily electricity consumption.
Climate and Runtime: In Denver, furnaces might run 8-12 hours daily during January cold snaps. Warmer regions see 2-4 hours of daily operation. Your location dramatically affects monthly kilowatt-hour totals.
Furnace Age: A 15-year-old furnace with worn bearings and dirty components draws more power than when new. The motor works harder to push air through restricted passages.
Filter Condition: A clogged filter forces the motor to work harder, increasing amperage draw. Changing filters every 1-3 months maintains proper airflow and keeps electricity usage down.
Calculating Your Gas Furnace Electricity Cost
Knowing your actual costs helps with budgeting and generator planning.
Step 1: Find your furnace’s wattage rating on the data plate inside the blower compartment door. Look for voltage and amperage. Multiply these numbers together. A furnace running on 120 volts at 5 amps uses 600 watts.
Step 2: Estimate daily runtime hours. Most furnaces run 6-10 hours per day in winter.
Step 3: Calculate daily kilowatt-hours. Multiply wattage by hours and divide by 1,000. A 700-watt furnace running 8 hours uses 5.6 kWh daily (700W × 8 hours ÷ 1,000).
Step 4: Find your electricity rate on your utility bill. The national average is 17 cents per kWh. Denver residents typically pay 12-14 cents per kWh.
Step 5: Multiply daily kWh by your rate and days per month. That 5.6 kWh furnace costs about 76 cents daily at 13.6 cents per kWh. Over a 30-day month, that’s $22.80 just for the electrical portion.
| Daily Runtime | Monthly kWh (700W furnace) | Monthly Cost (14¢/kWh) |
| 6 hours | 126 kWh | $17.64 |
| 8 hours | 168 kWh | $23.52 |
| 10 hours | 210 kWh | $29.40 |
| 12 hours | 252 kWh | $35.28 |
Generator Sizing for Gas Furnaces
Power outages can leave you without heat during winter storms. A backup generator keeps your furnace running.
Minimum Generator Size: Add 25% to your furnace’s running wattage. This accounts for starting surge. A 700-watt furnace needs at least an 875-watt generator.
Recommended Sizes:
- Small furnaces (400-600W): 1,500-2,000 watt generator
- Medium furnaces (600-900W): 2,000-2,500 watt generator
- Large furnaces (900-1,200W): 3,000-3,500 watt generator
A 2,000-watt portable generator handles most residential gas furnaces comfortably. This size also powers a few lights and your refrigerator during outages.
Whole-house standby generators typically start at 7,500 watts. These automatically switch on during outages and power your entire electrical panel.
Reducing Your Gas Furnace Electrical Draw
Simple changes can lower your electricity costs.
Upgrade to Variable-Speed Blower: This modification costs $800-1,500 but saves 30-50% on fan electricity. The payback period runs 5-8 years.
Install a Smart Thermostat: These devices optimize heating cycles and reduce unnecessary runtime. You’ll save 10-15% on both gas and electricity costs.
Seal Ductwork Leaks: Use mastic sealant or metal tape. Properly sealed ducts improve airflow, reducing blower motor strain.
Change Filters Regularly: Set a reminder for every 30-60 days during heating season. This keeps your blower motor from overworking.
Schedule Annual Maintenance: Technicians clean blower wheels, lubricate motors, and check electrical connections. These services maintain designed efficiency levels.
Add Home Insulation: Better thermal performance means shorter furnace runtimes. You’ll use less gas and less electricity.
When replacement time comes, Milehi Hvac offers furnace installation services in Denver with detailed energy savings analysis.
Conclusion
Gas furnaces use 400-1,200 watts of electricity, with most homes averaging 600-800 watts during operation. This adds $20-40 to your monthly electricity bill in winter months.
Understanding your gas furnace power consumption helps with generator sizing, energy budgeting, and making smart upgrade decisions. Regular maintenance keeps your system running efficiently.
Need expert help choosing an energy-efficient furnace? Contact Milehi Hvac for professional furnace installation services in Denver. We’ll help you find the perfect system to reduce costs and keep your home warm all winter.
FAQs
Will a 2000-watt generator run a gas furnace?
Yes, a 2000-watt generator handles most residential gas furnaces comfortably. Standard furnaces use 600-800 running watts with starting surges around 900-1,200 watts. This leaves enough capacity for a few lights and small appliances.
How many amps does a gas furnace use?
Gas furnaces typically draw 5-15 amps at 120 volts. Smaller units use 5-8 amps while larger systems with powerful blowers draw 10-15 amps. High-efficiency models with ECM motors often use fewer amps.
Can a gas furnace run without electricity?
No, modern gas furnaces cannot operate without electricity. They need power for the ignition system, blower motor, and safety controls. Even though natural gas provides the heat, electrical components are essential for safe operation.
Do variable-speed furnaces use less electricity?
Yes, variable-speed furnaces use 30-50% less electricity than single-speed models. They adjust blower speed based on heating demand rather than running at full power constantly.
How much does gas furnace electricity cost per month?
At average rates, a gas furnace adds $20-40 to monthly electricity bills during winter. A 700-watt furnace running 8 hours daily uses about 168 kWh monthly. At 14 cents per kWh, that’s roughly $23.50 for the electrical portion of heating.
