Pleasant surprise on the low power consumption of my new 2017 iMac, and I haven't seen this mentioned before in other threads so I thought it might be helpful for those making buying decisions: Note: All power measurements are from a Belkin Conserve Insight watt-meter: My old machine: 2009 Mac Mini 2.0GHz, 256GB HD, 4GB RAM: 26 watts Dell SP2208WFP monitor: 41 watts Dell 1901FP monitor: 36 watts Labtec LCS 2422 speakers: 6 watts Total dual monitor Mac Mini setup: 109 watts New Machine: 2017 27 inch iMac, 4.2 GHz i7, 1TB SSD, 16GB RAM, Radeon Pro 580 graphics: 40-50 watts in light use. That's an efficiency improvement of about 60 watts, with all the advantages of a 5K screen and the headroom of a quad core CPU with hyperthreading, so I get the benefit of power when I need it and energy efficiency when I don't. I know that the Apple help site says that the 2017 27 inch iMac consumes 71 watts at idle, but that configuration was 64GB RAM and 3TB fusion drive. My system power's usage with an SSD and less RAM is a real-world 40-50 watts for web browsing and office applications, with occasional spikes to 60 or 70 watts. I know that I have gone from two monitors to one, but the 27 inch 5k monitor is making a great first impression. Quite easy to place two documents side by side, and much sharper resolution with a retina display. Speaker sound quality is excellent, by the way. Better than the freestanding speakers I was using. They have been retired. Fan noise is unnoticeable. It's easier to hear the Seagate portable hard drive attached to the iMac than to hear the iMac fans. I'm sure it will spool up when needed but for light use it is essentially silent. Conclusion: for web browsing and office applications my new computer uses about 60 watts less than my old computer, is essentially silent (lower fan noise than my old Mac Mini), and provides an otherworldly improvement in computing power. Your mileage may vary. August 6th update: Power consumption varies with screen brightness by about 40 watts. In a brightly lit room near a sunny window the iMac is at nearly full brightness and power consumption is at 70 to 80 watts. At dusk with room light off the iMac is at about 1/8 brightness (settings menu, Display) and power is about 36 watts. My initial measurements were likely with the monitor in moderate room light.