Energy star dryers
The EU has had energy labels for quite some time now, but before the advent of heatpumps being the norm, there were few A rated dryers.
One particularly interesting aproach was the White Knight A rated vented dryer.
It had 5 electronic dryness settings, 2 heat settings and 2 modes: Speed and Eco.
The "Speed" setting made it operate like a normal vented dryer with a C rating.
On Eco, the rating cycle took 6-8 hours. All it did was tumble, no heat at all.
The motor was about 200-250W, so it never used more than 2kWh and results were apparently just as good as with heat.
Sure you had to use that over night and I wouldn't want my delicate clothing tumbled that long, but for bedding or towels, why not?
Point being that with vented dryers, the closer you get to line drying, the more efficent it gets.