I have some experience in heating greenhouses by flues, hot water and steam, and I suppose all have some advantages over the other, but were I to heat more houses I think I should prefer steam to all others.

If I should attempt to answer Mr. Holley's questions in a late Monthly I would say, in the first place secure a good boiler with sufficient capacity to do the work without crowding. If you are to run one low pressure, then two-inch pipe is best; if high pressure, then 1 1/4 inch pipe will do as well. It is difficult to say whether a five-horse-power boiler is sufficient to heat a certain house, for much depends upon location and exposure; but four houses connected will heat easier than one alone in proportion. One boiler will heat four houses if of sufficient capacity for the business. You can heat one-third more space with steam than by any other process, with same consumption of fuel. I would grade all pipes away from the boiler, that is, let the pipes from the boiler fall about one inch in eighteen inches, with the returns back about the same, so the condensation will follow along with the steam. Then there can be no clashing or noise.

Much depends upon the kind of boilers and connections about how long it will run without attention. Many boilers will not keep steam over four hours without replenishing the fire. All such are not suitable for the purpose. The boiler should not be too high, but should have large fire capacity. In my greenhouse heated by steam, it is in rather a sheltered situation, is a lean-to, and faces south. The boiler is of cast-iron, fifteen-inch grate, with one run of two-inch pipe out under the back side of the bench and back under the front side to the boiler. The house 13x60 feet; say 120 feet of pipe. There has been no trouble in keeping this house at 500 any cold night we have had for the last three years. Never had to sit up with this fire; could always leave it at 9 P. M. and find steam on at 7 o'clock in the morning. With the hot water boiler we have to watch with it all cold nights for the last seven years. I have raised the temperature in this house ten degrees in as many minutes. With ten pounds of steam you can fill the house with it, and it is very effectual in suppressing the red spider.