

A 12 oz glass bottle takes roughly 1100 BTUs to melt the glass for. That is conveniently, roughly, 1.1 cubic ft of natural gas.
60,000 BTU/hr is a very common size for natural gas HVAC furnaces. That’s basically a bottle a minute, just to give people an idea.
There are other inputs of course, but furnace net efficiency is around 2200 BTU/lb
Yeah it’s like 30% less heat input to melt cullet and you save raw materials. The problem is the quality impact. It’s a similar problem with paper recycling. Part of that is the fault of consumer preference, and I think that’s changing.
https://www.aigmf.com/docs/105/Cullet Sorting Technologies.pdf
Some info on the challenges