During the December 2025 polar vortex, variable-rate natural gas customers saw their supply rates spike 47 percent in week one as Henry Hub commodity prices ran above $14 per MMBtu. Locked-rate customers paid the November contract price through the entire cold snap. The locked-vs-variable bill gap on a typical home was $180 to $310 for the month. Here is the math behind why fixed-rate gas wins during a polar vortex and how to time the lock for the next winter event.
What happened in December 2025
A deep cold-air mass moved south from Canada the week of December 14 to 21. Temperatures in the Chicago to Boston corridor dropped to -10 F to -22 F. Heating load on the interstate pipeline system hit the year peak.
Henry Hub spot natural gas prices spiked from $3.80 per MMBtu (December 8) to $14.40 per MMBtu (December 17). Pipeline capacity charges spiked similarly. Variable-rate retail gas customers absorbed the spike in the next billing cycle.
Who paid what during the cold snap
Variable customers in the PJM and ISO-NE footprint saw December bills 32 to 47 percent above their November bills. The typical PA, OH, and NJ household variable bill ran $310 to $450 vs the locked-rate equivalent of $180 to $230.
Locked customers who had signed September contracts at $0.78 per therm paid that rate through the entire spike. The supplier had hedged the contract at signing and absorbed the spike. The customer paid the contracted rate.
How to time the lock for the next winter event
Lock in August through October. Supplier offers price most aggressively in this window because winter spike risk has not yet priced into the forward curve.
Lock for 18 to 24 months. A 12-month lock signed in August exposes you to next winter at re-rate time, which is the worst possible timing for re-shopping. An 18 to 24 month lock takes you past two winters.
Lock the rate before the next reset.
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Quick answers from the editorial desk
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