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If you're asking what the term stove pipe means, it's when the empty case of a fired cartridge is protruding from the ejection port.
Condution
240V is much more effecient, and you can put more heaters on a 20 amp circuit than you can a 120V.
A stove. Hopefully, a gimballed stove!
Usually 18 inches min. unless otherwise specified by the manufacturer.