Some residents are reporting bills that are double what they were the month before, and the main culprit is no big secret. The recent bitter cold weather days have driven up heating costs for many.

Tiara Harris said her bill this month was $200, twice what she expected.

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The CPS Energy Customer Center on Wednesday was busy with people wondering why their bills were so high.

Resident Luis Gonzalez said his January bill was nearly $400.

“’Oh, my God. That’s way too much,’” Gonzalez said of his reaction to seeing this month’s bill.

“When we have these extreme temperatures, we’re going to see these high bills,” said Nora Castro, with CPS Energy.

January had nine sub-freezing days. December only had one, and last January had only three.

CPS says it comes down to a homeowner’s usage. Even if you set your thermostat at your usual temperature, it was so cold that your system had to work a lot of overtime.

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Three days this month, San Antonio came close to setting all-time records for energy usage.

“We have a really helpful tool called My Energy Portal, and they can actually track their usage all month long,” Castro said.

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People can see exactly what they used by the day and even compare their usage to that of their neighbors.

While the weather is the No. 1 factor for bill spikes, second is the efficiency of a unit. Old ones may cost homeowners more. And if you haven’t weather stripped, it’s money right out the doors and windows.

RELATED: CPS Energy Casa Verde program provides free weatherization services

Another note to consider: Billing cycles can vary. If you have a bill that covered more days than usual, that will make a difference.

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