I'f your havinga pot bellied stove, I'd think about looking out for a solid fuel boiler & pipes it will spread the heat better around the greenhouse. Maybe you could even use the heat store principle & have the path as a 10ft x 2ft heat store to leach out over night.

Also, line your greenhouse with bubble wrap that will help no end with heat retention & get the 1" bubbles rather than the small ones - you don't loose so much light.

Have you thought about Propane heaters? they are quite efficient to use and you can always have two bottles and an automatic switch over so you won't run out.

__________________
ntg

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Remember that a lone amateur built the Ark.
A large group of professionals built the Titanic

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