Is it true that the more stuff there is in the freezer the less energy it consumes? I’ve been told that keeping air cold takes more energy than keeping solid stuff like water or meat cold, so you should keep the freezer filled to keep the electricity bill down.
Not exactly; if you never opened your freezer door it would make no difference whether it was full or empty, your freezer would run at whatever rate made up for the trickle of heat through the insulation.
The main burden on your freezer is cooling it down again once you’ve opened the door and let lots of hot air in. A full freezer has less room and so less hot air can enter. Plus, the frozen food acts as a buffer so that the increase in temperature isn’t as dramatic. The same total amount of heat still has to be pumped out, but the compressor doesn’t face as huge a load at one time.