• rcbrk@lemmy.ml
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    3 years ago

    You’re not considering the energy required to smelt the iron.

    Iron filings (in a collected quantity high enough to make manufacturing these heat packs worthwhile) are not a waste product, they are recycled – saving the smelting of that much new iron.

    Sawdust+iron heat packs are a very useful and non-hazardous product, for sure, but aside from situations where a hot water bottle is impractical, hot water bottle still wins.