In reply to the inquiries of your correspondent, E. Holley, I may state: 1st. The number of radiating [pipes required to heat his plant-house 100x20 feet will depend on its situation, the workmanship and material in its construction, and the free flow of the pipes. 2d. The greater surface a heated body exposes to a cold atmosphere, the more heat it gives out. Many pipes emit more heat than few; so that the bore of the pipes as a whole equal each other; smaller pipes are more economical. 3d. The ascent and descent should be as gentle as possible. 4th. Hot water is safer and as cheap. Where gentle heat is needed the water is not allowed to boil, but to make steam it must boil; 212 Fahrenheit boils water. Plants could not live in that, but the steam carries off the heat to the colder parts of the house. There is danger from explosion by steam, but there are safety valves for both hot water and steam systems to prevent this danger.

For forcing cut flowers, and propagation of tropical plants in winter, steam heating and many small pipes are best. Either hot water or steam is preferable to drying brick flues.

They both will maintain a good heat from 10 p.m. to 7 A. m., but if the temperature outside falls greatly through the night, or a fierce frosty wind strikes against the house and sweeps over it, the temperature inside the house will surely lower. Much depends on a careful fireman and the kind of fuel he uses.

The cheapest and safest plan with the iron pipes;s to let the furnishers put the whole up and strictly follow their directions in the future management.

All the boilers advertised in the Monthly are great improvements on those of long ago. It is about fifty years since I first saw both hot water and steam heating used in planthouses, and forcing pit frames for pineapples, in North Europe.

The larger the boiler surface exposed to fire, the more heat it takes in, and the flow of the heat goes faster and farther, either by water or steam. In that there is a large economy in fuel.

[These general hints will be found very useful to the novice, but we may remind the reader that though the question has been often asked in our columns, no one has answered why hot water pipes must be made to ascend. Hot water as well as cold will travel faster going down hill. Ed. G. M.]

In accepting the task imposed upon me of giving my experience in steam heating, I have done so fully aware of the fact that I am standing before those far beyond me in business experience. I therefore claim your indu1-gence. So impressed am I, however, with the importance of steam-heating in connection with our business, and so fully am I convinced of its superiority over all other modes of heating that I gladly avail myself of this opportunity to add my testimonial to the many that steam has already secured. Last winter, the first season in my career as a florist, we had five greenhouses, two heated by Hitchings' boiler, the remaining three by means of flues. I soon became convinced that both ways were far from perfect, and in the anticipation of building more houses I immediately commenced looking for some more improved method. I became impressed with the idea that steam would be the most effectual and desirable means, and of course read all the articles in our various journals for and against it with deep interest. I corresponded also with all the florists in the United States who were using steam wherever I could find them.

Besides this, I sought the advice of some of my much esteemed brother florists in Philadelphia many of whom have been so kind and generous in their associations with me. I found much to encourage me in my pet theory, and yet much to deter. Instances were quoted me of men who had been ruined through its use, and indeed I must acknowledge that many times I would decide at night that it would not be safe to try the dangerous experiment; that I must stick to the hot water system; yet invariably a night's sleep would dispel the misty doubts, and the next morning would find me possessed with a greater longing for steam than ever. Late in the winter, having heard of some greenhouses in Flatbush which were heated by steam, I determined to visit them. I found the proprietor far from being perfectly satisfied, and again my ardor was dampened. I had read in the Gardeners' Monthly the advertisement of the Exeter Heating Apparatus, and upon writing to the company I received from them such information as decided me to go to Boston and see one of their boilers in operation.

I felt I had found the right thing; indeed, so much was I pleased that before I left Boston I bargained with them to heat my ten houses.

Fig. 1 shows how the steam enters over the door.

Fig. 1 shows how the steam enters over the door, and is then run over to the coils situated on the sides of the house. The black dots represent the valves controlling the coils.

I will now give a description of my boiler. The Exeter heating boiler consists of a series of sections rectangular in form, two feet long, two and a half feet high, three and a half inches thick. Each section is cast with eight openings through it two inches by twelve inches. These sections being arranged over the fire two inches apart, transversely to the draft, the openings form fire tubes (although not continuous, as the spaces between the sections unite them into one space), and increase the heating surface, while their walls tie the flat sides of the sections together.

Every angle is rounded inside and out, and the bottom and top faces of each section have wave-like forms, to permit expansion and contraction. The lower and upper parts of each section are connected by an extra heavy pipe, extending through the wall of the setting to a main outside drum common to all. There is an automatic damper regulator which is attached to the boiler, and operated by the steam it can be adjusted to any desired pressure (say two pounds in cold weather), and when the steam reaches that pressure it immediately acts on the automatic regulator, shutting the draft door and closing the damper in the pipe leading to the chimney, thus checking the fire and preventing an increase of steam. As the pressure decreases slightly, the lever falls and opens the draft. In safety appliances there are a safety valve and safety plate.

From the upper drums (spoken of in the description of the boiler) start the steam main, which is perpendicular for twelve feet, and then branches off and runs through both of the sheds; - the pipe always growing smaller the farther it gets away from the boiler; at the center of each house this pipe is tapped and the coils run in the houses. I have a drawing of a coil. These coils have a fall of nine inches in every one hundred feet, so that all condensed steam runs to the lower end, where a drip is taken out of the bottom of the manifold (this drip also having a fall of nine inches to one hundred feet) and runs into a main drip which runs the entire length of the shed; it is underground, and has a fall of two feet towards the boiler. In my five houses, 22 feet by an average 115 feet, there are 16,445 cubic feet each, or 82,225 cubic feet of air in all to be heated. These houses each have about 1,000 feet of 1 1/4 inch pipe. In my other five houses - three 12x96 and two 18x96 - there are 50,976 cubic feet of air to be heated, and there are about 3,000 feet of one-inch pipe; so that in all we have 133,201 cubic feet of space to heat and 5,000 feet of 1 1/4 inch and 3,000 feet of inch pipe do it admirably.

Before speaking of the advantages gained by steam I would like to say that each feed which supplies the coil has a valve on it; each drip has a valve; each coil has an automatic air valve, and upon each end of the coil is a manifold which is so arranged with a system of valves that I can use as many pipes as the weather makes necessary. The advantages of steam as they occur to me : (1) The pipes certainly do not occupy one-fourth of the space demanded by hot water pipes; they are usually against the partitions, and quite out of the way. (2) The heat can be graduated to the greatest nicety, distance from the boiler being of no consideration, those farthest distant can be heated, without heating those near at hand, if desired. Should you want to keep a house cold, let the valves remain closed; if not so cool, turn on one pipe; warmer, two pipes, and so on. (3) As to the dryness of the heat from steam pipes - which some claim as a disadvantage - I must own that I fail to see why the heat radiated from iron pipes should be changed at all in character as to moisture, whether the heating medium inside the pipe be steam or water. (4) A most important advantage in steam-heating is the great economy in labor.

With five houses last winter we required eight fires in the coldest weather, quite distant from each other in location. Now with more than double the amount of glass, we have but two fires in the same boiler hole, side by side. Then again, no fire can be more easily managed, the automatic dampers work to a charm; indeed, as far as such a thing is possible, it seems to me the apparatus is almost self-regulating. With reference to economy of fuel, I consider it compares very favorably with other means. I should suppose that we burn about three tons of coal per week, and we cover an area of over 20,000 square feet. Probably some of my older and more experienced friends can better form a comparison in this particular than I.

Fig. 2 shows a coil with manifolds on each end.

Fig. 2 shows a coil with manifolds on each end, and the drip taken from one of them. The letter A represents an air valve.

Fig. 3 shows a front view of section.

Fig. 3 shows a front view of section - also showing the flue pipes formed, AAA.

Fig. 4 shows an end view of section, showing openings into which the pipes running into the water and steam drums are.

Much as I favor heating by steam, I do not think that I can too strongly protest against entrusting the applying of it in greenhouses to the care of those who do not fully comprehend the peculiar necessities of the case. Many good steam-fitters, with much experience in applying heat by steam to ordinary buildings, would fail probably in giving satisfaction in greenhouses. But properly applied, I think it cannot fail to produce successful results, and the happy florist who introduces it into his houses will doubtless join me in thinking steam heating without a rival.