The math there gets pretty bad pretty fast. A cubic foot of snow represents ~15 lbs of ice. That corresponds to at 144 BTU to melt a lb of ice, that means you need at a minimum 2160 BTU of fuel (assuming 100% of your heat goes to melting the snow). A gallon of gasoline represents about 114,000 BTU, so each gallon of gas could clear, in a best case scenario where you can capture 100% of the heat, only 50 cubic feet of snow. That's a 10-foot by 10-foot area covered in 6 inches of snow.

But even that's in the dream scenario where somehow your snow is in a sealed, insulated space. In the real world, snow tends to be outside, in the cold air, which is very eager to sink and replace any hot air you make at ground level. So you're losing any heat that warms the air at all. And all that air in the snow makes it a fantastic insulator, meaning the vast majority of your heat isn't going to penetrate.

Interestingly, this same phenomena makes melting snow from underneath much more effective (as the great insulating snow captures the heat). You still need to grapple with the kinda nuts amount of energy it takes to melt ice, but at least you're not wasting 90% of it.

Yes, but it's nowhere near as effective as you might think. Also, due to its ineffectiveness, it ends up costing a LOT of fuel.

those handheld propane torches, oft used for weedburning on asphault/concrete, are very good for clearing "post snow clean up ice patches, IE tire treads that iced over, foot prints.

Not useful for snow as you'll quickly be swimming and out of propane

xkcd explored this question. too fuel-inefficient to be practical. much better to use that same fuel to run a giant snowblower (and move the snow rather than melt it).

https://what-if.xkcd.com/130/