Sean you have the most intelligent response here.
( peak loads during summer and winter )( base loads year round)
As a energy rater here in California I have seen anywhere between $ 125 to $700 during summer. Depending on many factors like: location ,The home air changes per hour ( ACH50), bad or no insulation, windows, Bad air and heating installations ( THAT IS A SUBJECT ITSELF), pools ( if applicable), irresponsible people, not maintaining H VAC equipment, and many more....Most people buy for the properties aesthetics and completely forget the house is a system itself. How the home is put together and the quality of the air conditioning and heating system / maintenance are fundamental factors for comfort and energy use.
I suggest asking for previous bills for the home - ask how the ac and heating system was used previously ( conservative or non conservative) - Was the equipment maintained properly and all the above and more.
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