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.
I think there must be a great many readers of your paper that heat their houses with furnace heat that would be pleased to know how to heat a small greenhouse by the same fire.
I know that I should have been very much pleased to be informed how the thing could be accomplished last fall. Now I know by practical experience, and if you think it will be of use to any one you are at liberty to use it.
My greenhouse, or perhaps it might be better named pit, is a lean-to, adjoining the house, about 12 feet square, facing south, about 3 feet of it being under the piazza. The heating arrangement is what I intend to refer to principally, as follows:
I procured a copper boiler, holding, perhaps, 2 gallons, made to fit a section of the fire-pot of the furnace. From this I led the flow pipe (1-inch gas pipe) to the ceiling of the basement, thence to the greenhouse, about 20 feet from the boilers, along the side to the front, where I connected with a coil of l 1/2-inch gas pipe, which passes four times across the front of the greenhouse, then returns to the boiler with a 1-inch gas pipe, to be heated and go over the same ground again. It requires no care, about one-half pint of water per week, and works perfectly; and if flowers could say anything they would say that it suits them perfectly, too; not having the gift of speech they do the best they can by looking their very prettiest. At the present writing I have in bloom Auriculas, Azaleas, Roses, Hyacinths, Pansies, Cyclamens, Camellias, Choroze-mas, Abutilons, etc, all in perfect health, which plants never have when heated by stove or furnace heat.
If you conclude to publish the above, you will have to dress it up a little. If there is anything that you cannot understand, and think it worth a letter of inquiry, I will answer it. If I was to wait till I had time to write in shape fit for publishing I am thinking my plan would never reach you; and if on reading the above scrawl, you think that the best place for it is in the basket under the table, I shall offer no objection.
One thing I really forgot, which is essential to the working of hot water - keep all the pipes above the level of the bottom of the boiler. This I learned by experience. I tried to have my return pipe lay on the floor of the basement, which was about 18 inches below the bottom of the boiler, but the water would not flow properly; did not work at all satisfactory until I changed it to have all the water used a trifle higher than the bottom of the boiler. The expense of the whole heating arrangement was about twenty-five dollars. The boiler must be made to fit the fire-pot of the furnace very close; and I think, probably, 2-inch pipe for the front pipe would be better than 1 1/2. This winter has been a very mild one, but I have no fears but that with a few mate for covering I shall be able to keep frost out in a severe winter. If the pipe has to be carried far before entering the greenhouse, it will be necessary to cover it with a coating of asbestos or sawdust, or some good non-conducting material, otherwise a considerable amount of heat will be lost by radiation. With such a covering it can be carried quite a long distance without much loss of heat. Probably two 4-inch nines across the front of greenhouse would be much better than four l 1/2 ones.
This is only suggested; I have only written as I have it in operation. I hope some one will give you something better before next winter for heating small houses.