There are only two recognized methods of heating our glass structures, steam and hot water. Brick flues have gone and electricity has not come, but it may. Some fifteen years ago heating greenhouses by steam came with a rush, although it had long been used as a means of heating dwellings and large buildings. Men who had been at first most sanguine about its superiority over water began to hesitate and consider whether after all hot water had not the most advantages. A patriarch of the business, Mr. Peter Henderson, being asked by the writer in 1889 which was the best way to heat, inquired what system I was then using. On being told "hot water," the reply came quick and brief, "Keep on with the hot water."
But after all this ebb and flow of popular favor it is now well established that with an improved system of piping, steam for many establishments is the cheapest and best, and although by no means claiming to know of steam what I do of the circulation of water, we will first consider
Steam as applied to heating greenhouses has several advantages over water. Heat is quickly produced by steam and sent through the houses in case of a quick fall of the outside temperature. It is also quickly reduced or entirely absent in the pipes should you see in the early morning that it is going to be a bright, warm day and no steam heat will be needed. This I consider one of its best features, for we all know how we have suffered with overheated houses when the water in the pipes would not cool.
With a number of pipes and a valve at each, a house with steam and proper attention can be kept at almost the desired degree. It is cheaper to put in a steam plant. The piping is much cheaper, sufficiently less to offset the larger cost of the boiler.
Steam is undoubtedly the best system when a block of houses is devoted to one purpose, but where two rose houses and two carnation houses are heated by one boiler it would not be so economical, because a month or more after no heat was needed in the carnation houses you would have to still make steam for the rose houses.
Where a dozen houses are used for many different plants water is to be preferred. Water can be heated to a temperature of about 140 degrees, just sufficient to take the chill off the house; a very slow burning fire will do this. With steam you must have sufficient fire to make steam or you may as well have no fire at all. If you wish only to fill one 1-inch pipe the boiler must be full of steam or none will pass into the pipe. Steam is most convenient for evaporating tobacco. Altogether, steam is the plan for large establishments, where four or five houses will want heat at the same time, and water is the best for houses where less quantities but greater varieties are grown.
Cast iron boilers of several makes are used by greenhouse men to generate steam, but wherever there is much work to be done a steel tubular boiler, return flue, is the best. If for locomotives, steamships and factories the tubular boiler is the best, why is it not the best for the greenhouse with some modification of the way the fire is applied?
I have seen some greenhouse boilers where the fire or heat from it first passed under the whole length of the boiler, then returned to the front by half of the flues and again returned to the rear by the other half of the flues. We believe that was overdoing it. On returning the third time the smoke would be so cool that it could not help in making steam, therefore it was no help. If the flame and smoke is carried beneath the boiler, returning to the smoke stack through the flues and the draught is what it should be, you will have got about all the heat from the fuel that is possible towards making steam.
This is a proper place to say something on fuel. We have within a very few years been compelled to use under steel tubular boilers several kinds and grades of coal. We think the most economical fuel, which gives the best all-round results, is soft or bituminous coal. The grade known as three-fourths lump is very satisfactory, that is, all dust and small particles that would pass through a 3/4 -inch screen are not present. Soft coal needs attention, so do the small sizes, pea and buckwheat, of anthracite, which some use because they can purchase it at a low figure. You can bank down soft coal for many hours, keeping in a fire, while there is little or no combustion going on; with added draught it is quickly made into a lively fire. Unless your draught is very powerful there is a serious objection to the larger sizes of anthracite, and more particularly coke. During the coal famine of two years ago we burned hard coal under a fifty horsepower boiler, and we never burnt up $5 bills so quickly. This hard coal, and still more, coke, will lay over the fire bars a red-hot fire, just what you want in a cast iron heater, giving little distribution of heat, but burning out the crown sheet of your boiler. This actually occurred with us with a boiler but a few months installed, and the boiler-maker who put in a patch told us the cause. Altogether, a good grade of soft coal is the most satisfactory and economical for a steel tubular boiler. There is one duty with soft coal that must never be neglected, viz., cleaning the flues. Once a day for this most essential part of stoking may do in mild weather, but when you are running the boilers to their capacity the flues should be cleaned twice a day. It will save your coal pile.
Many prefer to use old marine boilers that have been condemned for use where high pressure was needed. They may last a long time, but as in everything else a new boiler made for you is the cheapest in the end.
There are a few things connected with the care of a steam boiler worth mentioning, which never should, but sometimes are, neglected. One is to frequently open the valve on the blow-off pipe, which is or should be connected with the lowest part of the boiler, and into which any dirt or sediment is sure to settle. Simple as this is, we have known the day fireman to think it was the duty of the night fireman, and the night fireman also to shirk this little effort; between the two an accident occurred that might have been most serious. Water that is used over and over again, as it is in our greenhouse boilers, will deposit much less sediment than where a new supply of water is continually being supplied to make up for that constantly evaporated. Still, once a month your boilers should have a good wash out. It is easily done, and, like cleaning the flues of soot if you want to save fuel, is an economy that is worth while.