In a Denver winter, the furnace uses most of the gas. A gas water heater in Colorado uses about 13 to 19 therms a month, so in January nearly everything above that is heat.
Weather
NOAA counts heating degree days at Denver's airport. A normal January has 1,034. January 2025 had 1,211, 17% colder than normal. January 2026 had 947, 8% milder. The same house at the same thermostat setting needed about 28% more heat in January 2025 than in January 2026.
Last winter, December to February, ran 23% milder than normal. A normal winter this year will raise the heating part of the bill even if rates stood still.
Rates
Xcel's gas price per therm, before taxes and city fees:
| Starting | Per therm | Monthly charge |
|---|---|---|
| January 1, 2025 | $0.8747 | $13.00 |
| July 1, 2025 | $0.8526 | $13.05 |
| October 1, 2025 | $0.8653 | $13.07 |
| January 1, 2026 | $0.8941 | $13.32 |
| April 1, 2026 | $0.7303 | $13.32 |
| July 1, 2026 | $0.8045 | $12.99 |
| October 1, 2026 | $0.8031 | $13.02 |
| October 6, 2026 | $0.8782 | $13.82 |
The October 6 change is Xcel's gas rate case, about 8.6% on the average residential gas bill. The rest of the movement is the gas cost adjustment, Xcel's charge for the gas itself, which changes at least every quarter.
The house
If your therms rose more than the degree days did, something in the house changed. Look at the thermostat schedule first, then drafts, attic insulation and the furnace. Xcel's Home Energy Squad Plus visit runs a blower-door test and infrared imaging to find the leaks.
The decoder on the home page does this math for your own bill.
Common questions
What is a heating degree day?
Each degree a day's average temperature falls below 65°F counts as one. A day that averages 20°F adds 45.