If your Nicor Gas bill seems higher than expected, you're not alone. Many Northern Illinois residents experience significant bill fluctuations, especially during the cold winter months. Understanding the factors that influence your bill can help you make sense of the charges and identify potential areas for savings.
Nicor Gas serves approximately 2.2 million customers across Northern Illinois (excluding Chicago proper, which is served by Peoples Gas). As a regulated utility, Nicor provides both delivery and gas supply, though customers can choose alternative suppliers through the Customer Select program.
Illinois Winter Heating Costs
Northern Illinois winters are harsh, with temperatures regularly dropping below freezing from November through March. This creates a dramatic seasonal swing in natural gas usage—summer bills might reflect 10-20 therms (water heating, cooking), while winter heating can push usage to 150-300+ therms per month.
This 10-15x increase in usage is the primary driver of high winter bills. A typical Northern Illinois home might see bills jump from $40-60 in summer to $200-400 in the coldest months.
Fluctuating Gas Supply Charges
Nicor's gas supply charge changes monthly based on wholesale natural gas prices. In January 2026, the rate is $0.42/therm—a 50% increase from January 2025's $0.28/therm. These fluctuations directly impact your bill.
The gas supply charge typically represents 40-50% of your annual bill. When wholesale prices spike (as they did in winter 2022-2023), bills can increase significantly even without changes in your usage patterns. Learn more about how gas supply charges work.
Home Efficiency Factors
Several factors determine how much gas your home needs for heating:
- Home age and insulation: Older homes may lose 30-50% more heat than well-insulated newer homes
- Furnace efficiency: A 15-year-old furnace may be only 80% efficient vs. 95%+ for new models
- Thermostat settings: Each degree above 68°F increases heating costs by 3-5%
- Air leaks: Gaps around windows, doors, and outlets can significantly increase heating needs
Check Your Bill for Accuracy
Before assuming your high bill is due to usage or rates, it's worth verifying that the charges are calculated correctly. Check that your meter reading matches what's shown on your bill, and verify that the gas supply charge matches Nicor's published rate for that month.
Use our free sanity check tool below to see how your bill compares to typical Nicor Gas bills. If your effective rate appears significantly higher than expected, it may be worth requesting a bill review or having an independent verification performed.