Are Two Case Fans Costing Me $6.00 Every Year?
Maybe. I don’t know that I have enough data to know for sure. I stuck a Cloudfree smart plug running Tasmota onto my homelab server a few months ago. That got me messing around with maximum clock speeds and CPU governors. Switching and tuning governors brought my ancient FX-8350 server down from 2.2 kWh per day to 1.97 kWh per day while still allowing the server to crank up to 4 GHz when necessary.
This year, I pulled three of the four 4 TB hard disks out of my homelab server and replaced them with a single 14 TB USB hard disk. That gave me about a week’s worth of reading very near 1.65 kWh per day. I did some math on that!
(1.97 kWh - 1.65 kWh) * 365 days * $0.12 per kWh = $14.02 per year
Our electric bill is more complicated than this. Google says the average residential electricity rate is $0.15 per kWh. The twelve cents I’ve been using might be rounded down, but I am going to call it close enough. That means it costs around $7 to spin each hard disk for a year.
Part of this year’s hard disk gymnastics also involved moving the homelab server out of my office to the other side of the house. It now lives underneath the network cupboard.
I just had wires spilling out of the cupboard door for a few weeks. I drilled a new hole in the bottom of the cupboard and cleaned that mess up a few days ago. I also popped open the case and unplugged two 120-mm fans.
I don’t know how these fans were configured. They were plugged into the motherboard, so they may have been speed controlled. If they are speed controlled, the BIOS was set to spin them pretty fast!
It is tough to get a handle on what sort of wattage a computer is running at. The reading bounces around by at least three or four watts most of the time, and it is normal to spike a bit if there’s some activity. Even so, it was immediately obvious that numbers were trending something like 5 watts lower after unplugging the fans.
I checked power consumption after the next full day running on the Tasmota plug. I was really surprised to see a reading of 1.52 kWh for the day!
(1.65 kWh - 1.52 kWh) * 365 days * $0.12 per kWh = $5.70 per year
NOTE: 1.52 kWh happened to be the highest reading over a handful of days, but only by a bit!
My guess wasn’t far off. Math says that the homelab server was averaging 68.75 watts with the fans and 63.3 watts without the fans.
Is three dollars per fan per year a big deal? Definitely not, but if you like to fill up every available slot in your case with a fan, it might add up. I have cases with enough room for five $25 Noctua fans. That would be $125 in fans plus up to $15 per year to run them.
Maybe. Hopefully your fans are spinning down when things are already running cool!
I don’t think this is terribly exciting information, and since these particular fans were just running at a constant speed, I don’t even have all the information. I just figured that if the number surprised me, that it was worth writing a few paragraphs about it!