Ok, so about 6 months ago I installed a new automatic thermostat and it ended up being the wrong type and was not able to control the aux heat. I then bought a new one that was compatible and worked throughout the winter and did very well at keeping the house warm when I need it. However, when I looked at my bill that is usually around $170 in the summer and had been $270 with the dumb thermostat last year in January and February, it jumped to $400. The only thing that changed was that I installed a new thermostat that I thought would save me money and I did put a filter in the large return in the house as well as inside the unit under my house. Thanks in advance for any help you can provide!