I think that propane would be the better of two. the gos released by burning is CO2, while ail burners release co for the most part but the others are anyones guess. I would probably lower the cieling for the winter carefully, carefully with bubble wrap to confine the heat. the less gas you burn the less CO2 (less $$too ). CO2 is a greenhouse gas so it should have an insulating effect. dont forget that night is when plants need O2, so ventilation is a must !

Oh yeagh, I lived with an oilheater in my room for a while... never again,

John