Emergency Heating (Calor/Butane gas)

[Scythe13]

Outdoor heaters are made to a lower standard of efficiency, and do not have layered burning, e.g. look on the front of a calor heater, they have multiple layers of burning. This reduces the likelihood of Carbon-monoxide (CO) being released into the atmosphere.

The smaller outdoor camp gas heaters are pretty inefficient burners and do release some CO...as expected. But they are used in a well ventilated area, e.g. a tent. Which means less of a danger of carbon monoxide poisoning for the users.

Also, it's just a good security cover for the companies to write 'not for indoor use' on their stuff, so incase something does go wrong (in my opinion, it's very unlikely anything will go wrong) then they're covered and can't be sued.