To estimate energy cost, multiply your kilowatt hours by the cost per kilowatt hour. For example, if you ran the unit a constant one hour a day at the max 1500 Watt level, you would use 1.5 KW-hrs x 30 days = 45 kilowatt hours per month. At 30 cents per kilowatt hour (CA average cost), it would cost $13.50 a month. That's a rather extreme example, and I expect your actual cost to be less. The unit is best used to warm your body, not heat your house.