Just about every Texas building has air conditioning which is blasting for those 100 days of summer where it's often above 100 degrees. I'm surprised that a few days of cold is a bigger load than the crazy heat of summer.
Edit: Now that the sun is up and shining through our windows, the duty cycle of our (natural gas) furnace has dropped way off. I'm pretty sure our energy usage today will be less than on a 100 degree day.