Running your air purifier all day and all night will cost you about 86 cents a week, around $3.70 a month, and a whopping $44 bucks a year! These estimates are based on the average cost of electricity in the US, which is around 12 cents per kilowatt hour. And here's the thing, most HEPA air purifiers use up to 50 to 100 watts of juice per hour. So, keep that in mind!