In February I replaced my 15-year old Trane XE800 heat pump and single speed air handler with an XL16i and matching variable speed air handler effectively going from a 10 SEER unit to a 17 SEER state-of-the-art system.

Today I just received my first electric bill using the new system and I don't see any savings at all. Now keep in mind that it's somewhat difficult to compare Apples to Apples since the average monthly temperature was different this year versus last.

I don't know the formular for calculating energy effieciency but perhaps someone here may. Here is my latest usage:

Mar 05 - 29 days - 3583 kWh - Avg daily use 123.6 - Avg temp 36
Mar 04 - 31 days - 2764 kWh - Avg daily use 89.2 - Avg temp 42

On both systems I have a programmable thermostat and used the exact same settings. 68 degrees during the day, 65 degrees at night (11:00 PM - 6:00 AM).

The only thing that may be negatively affecting my energy efficiency is that I had an Aprilaire whole house humidifier installed at the same time and the HVAC tech connected it to the hot water line. Of course their may be some other issues as well. I appreciated any suggestions or advice.