This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
W. H. L., (post-office indistinct) writes: "Will you please give explicit direction for building furnace and flue to heat small or large greenhouses, in Gardener's Monthly and Horticulturist? or if such directions have been given in previous numbers will you please give their numbers and volumes that I may procure them, as I desire to build a furnace to heat a small greenhouse? Please state the price of the numbers also. I never saw Gardener's Monthly until this month's number fell accidentally into my hands, and as a lover of flowers am much pleased with it. I intend to become one of its regular subscribers."
[No particular directions can be given, because how to build will vary with each one's particular circumstances. In a general way one may say that it pays to have a furnace well built. The heat soon uses up a poor thing. Double doors are good. Single doors warp, crack, and soon loosen from their holdings. Good fire brick should form the sides and roof of the furnace, convenient the roof is best arched. The frame inside supporting the building arch can be burnt out. The mouth of the furnace, if possible, should be outside the greenhouse. Besides avoiding dust it is a saving of fuel, as when inside the fire is fed from the warmed atmosphere of the house. Where flues are made of brick, these should be soaked in water when about to be used, and the mortar should be of the best quality. The flue should be elevated from the ground, in order to keep the flue dry, which favors draught, as well as to save heat, as when the flue is in contact with the earth much is lost by conduction. - Ed. G. M.]