Illinois energy rates pre-filled from EIA. Estimate your heating cost below, and see the assumptions behind every figure.
Electricity: EIA Electric Power Monthly, Table 5.6.A, May 2026. That is a single month, not a 2026 annual average — annual state figures are not published until the following year. Natural gas: EIA Natural Gas Monthly residential price, winter average, Dec 2025 – Feb 2026, converted to $/therm. “Lowest running cost” is a calculation from those rates, not a survey of what people own: it is whichever system delivers a unit of heat for the least money in Illinois, comparing a heat pump at a seasonal COP of 2.4 against a 92% AFUE gas furnace. Rates vary by provider and season.
Illinois averages 28.3°F in winter. Cold winters (avg 28.3°F) and gas at $0.98/therm make a gas furnace about 63% cheaper per unit of delivered heat than a heat pump here.
On running cost alone a 92% AFUE gas furnace wins in Illinois: about $0.0107 per 1,000 BTU delivered, against $0.0291 for a heat pump at a seasonal COP of 2.4 — roughly 63% less. Gas is not available at every address, and a heat pump also cools.
Illinois electricity costs 23.85¢/kWh, about 29% above the US average of 18.44¢/kWh (EIA Electric Power Monthly, Table 5.6.A, May 2026). Where electricity is expensive, the efficiency of the equipment matters more: a heat pump buys the same heat for a fraction of the kilowatt-hours a resistance heater needs.
Compare Illinois against other states using our heating cost by state index, or use our free heating cost calculator to estimate your monthly spend.
Based on Illinois EIA rates: 23.85¢/kWh electricity (May 2026), $0.98/therm gas (winter average, Dec 2025 – Feb 2026).
| Heater Type | Small Home | Medium Home | Large Home |
|---|---|---|---|
| Electric Resistance | ~$554/mo | ~$923/mo | ~$1385/mo |
| Gas Furnace (92% AFUE) | ~$85/mo | ~$141/mo | ~$211/mo |
| Heat Pump (COP 2.4) | ~$231/mo | ~$385/mo | ~$577/mo |
How these are worked out. Whole-home heating for a full winter month, not a plug-in heater. We take Illinois's 28.3°F average winter temperature, which gives about 1,101 heating degree days in a 30-day month against a 65°F base, and multiply by a heat-loss coefficient of 300 (small, ~1,000 sq ft), 500 (medium, ~2,000 sq ft) or 750 BTU/hr/°F (large, ~3,000 sq ft) for an average-insulated home. That delivered heat is then priced at the rates above, at the efficiencies shown in each row. Those coefficients are round engineering figures, not measurements — they exist so every page on this site derives monthly cost the same way. A poorly sealed house can easily run double these numbers.
Figures above are calculated from EIA Electric Power Monthly, Table 5.6.A (May 2026) and EIA residential natural gas prices, using a seasonal COP of 2.4 for a heat pump in Illinois's climate and 92% AFUE for a modern condensing gas furnace.