[m0xte]

M600 fanless is around 15W full whack and 5.5W idle (measured). The CPU in it has a 4W TDP.

For that you gain:

Decent thermal design., A decent quality enclosure, A power supply (thinkpad brick), Two displayport holes, An SATA interface (M.2 form) for an SSD, Built in Wifi, A RAM slot you can chuck 16Gb in, 2 more USB ports.

There's no competition. I paid 79 GBP each for mine (I own 3). Pi is 57 GBP bare board.

Pictures. Mac mini for scale: https://imgur.com/a/jXjLusb

And on CO2, perhaps you should just do without it if it's a problem.