I have an Intertherm all in one electric AC/heating unit out on a slab outside my house. The unit works fine and the heater really heats up the house nicely however, every time I turn on the unit my power meter dial begins racing around so fast that it is a blur and my heating bill for one month is over $500 when I run the heat and only $120 a month when I do not run the heat. Do I have a defective heater or heating coil or blower motor or something? These things cannot be this expensive to run can they? The unit is several years old (maybe 10) and uses the heat coils. Can I replace the coils or the whole heating unit? These heating bills are killing me!