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How to Heat Your Hothouse: 1841 and Earlier


It’s the time of year when I visit old haunts, figuratively and literally. One of the oldest (literally speaking) is the Providence Atheneum, a library that’s been around so long that all the reading desks and chairs are antiques, and gardening books from the 1800s are still on the shelves, waiting to have their depths plumbed by people like me.

Plumbing, it turns out, is the mot juste. On this year’s expedition, I was surprised to discover that radiant floor heating was the heating system of choice for hothouses in 1841.

But as I started writing this post about it, I remembered a long-ago visit to the Alhambra, where I found radiant floor heating systems much older than that. Eight hundred years ago, the architect had caused a bath area to be built, and I remember the guide saying that the hot water was piped under the floors above, as heating. (Why is it that I can remember this comment from over thirty years ago, but I can’t recall the name of someone who introduced themselves five minutes earlier? Memory is indeed like a sieve, as a friend of mine used to say.) Since the entire palace is out of stone, the heating was probably welcome in the winter.

I am not sure if radiant floor heating was invented by the Arabs, but it seems likely. They were leaders in water engineering, likely due to their development of mathematics. I still remember the water in the gardens of the Alhambra, because they amazed me: though the place was neglected and crumbling around the edges (it was the very end of the Franco regime), all the fountains and pools and watercourses still worked: they had been designed to run on gravity alone, no pumps needed. On one staircase, where railings would normally have been, there were channels in the tops of the sidewalls, cascading water down to yet another pool and fountain. The flumes in my goldrush area sent timber from the mountains to port cities on the same principle, but they didn’t last nearly as long as the watercourses of the Alhambra gardens.

If anyone knows the history of radiant floor heating, or cares to speculate, I’d be interested to read your comments. But for now I will jump ahead to 1841, and Robert Buist’s The American Flower Garden Directory.

Garden writers of the mid-eighteen hundreds usually ran nurseries. They also bred plants, traveled long distances to see what other breeders were doing and to find new stock to introduce into their lists and breeding programs. Any aspect of gardening was their purview; there was much less specialization than there is today.

That’s because in 1840s U.S., gardening and plants were undergoing a huge boom. For the first time, the newly monied middle class could afford the ornamental plants and gardens that had been a rich person’s privilege in the century before.  Farmers wanted to know what the latest crops and plant techniques were. Literacy had become common, so there was a large readership for the books nursery owners began putting out, books that covered everything from the poetic values of tilling the soil to how to deal with the Rose slug, one of the catastrophic insect invasions of the 1800s.

Hothouse building was definitely on the agenda, and in The American Flower Garden Directory,  Buist tackles the construction of hothouses and greenhouses. He describes the siting of the hothouse: “…set the front directly to the south. Any deviation from that point should incline to the east.” And he gives a detailed description of the heating system.  “As workmen are not generally conversant on the subject, nor yet understand the effect or distribution of heat in these departments, we will give minute details on their construction.”

Coal- or wood-fired furnaces were the basis of the heating system  (wood-fired furnaces had to be built twice as big as the coal ones). The cheaper way was to run flues from the furnace through the greenhouse.

“Where capital, taste, and practical science can be united, a more elegant disposition of heating conveniences can be adopted: an excavation should be made for the flue to pass along under the pathway, which pathway may be a casting of iron, or wooden slats, fancifully put together, and at least six inches above the flue.”

But the flue system created problems with smoke and coal gas–dangerous to humans as well as plants. By adding a small boiler to the furnace (he recommend a size about 2 feet (about 61 cm) by 2 feet, and 4 inches (10.2 cm) wide), hothouse owners could have fumeless heating that was better for them and the plants.The boiler was built of cast iron or copper, with a zinc or copper lid. Two pipes were attached to the boiler, one to run hot water through the flues, the other to take the cold water back to the boiler for reheating–a simpler version of the way a boiler works in a steam-heated apartment building.

Clearly, it was the day of different manufacturing methods and abundant cheap skilled labor. Buist expected the incipient hothouse owner to easily find workmen who could build not only the boiler and the plumbing system, but the many wooden frames needed for the 6 by 6 inch (15.2 cm) panes of glass he thought were ideal. But a handy person today could easily rig a similar system for a hothouse, using modern materials.

Next post: How to Heat Your Hothouse: 1841 and Later


Robert Buist, The American Flower Garden Directory, Philadelphia, Carey and Hart, 1841

Great Buildings website

{ 5 comments… add one }

  • Helen/patientgardener December 23, 2008, 11:30 am

    Is this the same sort of system the Romans used – I think it is called hypercaust?

  • Nancy Bond December 23, 2008, 2:50 pm

    A fascinating read! (Merry Christmas, Pomona!)

  • Pomona Belvedere December 23, 2008, 7:52 pm

    Patient Gardener, I was impressed at your knowledge of hypercaust. I looked it up online, and it appears to be similar to the flue system of heating (without the water pipes and boiler)–there are pictures with brief descriptions at http://www.mylot.com/w/photokeywords/hypercaust.aspx I never knew about this before, thanks for bringing it to my attention.

    Nancy, glad you enjoyed it, and Merry Christmas to you, too.

    More ideas and history welcome!

  • catmint December 27, 2008, 3:48 am

    I don’t have anything to add about the hothouse construction but you did start me thinking about the relationship between accepting the limitations of the climate like indigenous people did /do, versus using technology to grow stuff that is not suitable for the climate. I know I was surprised to visit the tropics and see plants growing wild that are fussy indoor plants here. I visited Siberia recently, didn’t notice any hothouses, they pickle cabbage and onion , have a restricted diet in winter and make up for it by gorging on berries and other fruit in summer. My other comment is about the Atheneum Library. One exists in Melbourne, it started in the 1830s and is full of antique furniture as well. Pomona, you have given me the idea to go there to check out their old gardening books! Thanks for a stimulating post – and fascinating blog.

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