How Many Watts Does a Gas Furnace Use? (Blower Motor Power)

A gas furnace typically uses 300 to 800 watts of electricity during a heating cycle — far less than the 10,000–24,000 watts an electric furnace consumes. About 80–90% of that electricity goes to the blower motor, with the rest powering the gas valve, inducer motor, control board, and igniter. A variable-speed (ECM) blower uses 75–200 watts on low speed versus 400–700 watts for a single-speed motor — saving $50–$150/year in electricity.

This matters for sizing a backup generator, understanding your electricity bill, and recognizing the hidden electrical operating cost beyond just gas.

Wattage Breakdown by Component

Annual Electricity Cost

Variable-speed ECM blowers save $50–$150/year in electricity versus single-speed motors. They also deliver better comfort and quieter operation. The $400–$800 upgrade cost pays back in 3–8 years from electricity savings alone — plus the comfort benefits.

Generator Sizing for a Gas Furnace

A gas furnace needs electricity for the blower, controls, and igniter — so it won't work during a power outage without a generator or battery backup.

Pro Tip

A 3,500–5,000 watt portable generator is sufficient to run most gas furnaces plus a few essentials (lights, refrigerator, phone charging). If you have a variable-speed furnace, you can get by with a smaller 2,000W generator. Always run the generator outdoors and at least 20 feet from windows and doors to prevent carbon monoxide poisoning.

Gas Furnace vs. Electric Furnace Wattage

This massive wattage difference is why gas furnaces remain practical during power outages with a modest generator, while electric furnaces are essentially useless without grid power.

Real-World Examples

Real-World Example

Example 1: The Millers — Generator Sizing in Ice Storm (Louisville, KY) During a winter ice storm that knocked out power for 3 days, the Millers ran their gas furnace on a 3,500W portable generator ($450). The furnace (single-speed PSC blower) drew about 600W running. They also powered their refrigerator (150W), a few LED lights (30W), and phone chargers. Total load: ~800W running, well within the generator's capacity. Their house stayed at 65°F while neighbors with electric heat had no option.

Real-World Example

Example 2: The Nguyens — ECM Motor Savings (Denver, CO) When the Nguyens replaced their 18-year-old furnace (single-speed PSC blower, 600W) with a new 96% AFUE model with a variable-speed ECM blower (average 200W during heating), their winter electricity bill dropped by $18/month. Over a 6-month heating season, that's $108/year in electricity savings — on top of the gas savings from the higher AFUE rating.

Key Takeaways

Key Takeaway

A gas furnace uses 300–800 watts — mostly from the blower motor. This is tiny compared to an electric furnace (10,000–24,000W).
Variable-speed ECM blowers use 60–75% less electricity than single-speed PSC motors, saving $50–$150/year.
A 3,500–5,000W portable generator can power a gas furnace during outages. Electric furnaces cannot practically run on generators.
The startup surge from single-speed motors is 3–4× the running watts — size your generator for surge, not running watts.
Annual electricity cost for a gas furnace blower: $43–$190 depending on motor type and runtime. A small but real addition to your heating costs.

Frequently Asked Questions

Sources

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