40 VEGETABLE FORCING 



using hot water, and they also claim economy in fuel 

 consumption, and better atmospheric conditions for the 

 growth of the plants. Some growers have a combination 

 of steam and hot water. They use the steam only in 

 extremely cold weather and for sterilizing the soil, and 

 also for operating the pumps. 



The differences in the various methods of steam and hot 

 water heating are so great that the two general systems 

 can scarcely be compared. It may be said, however, that 

 there is an increased tendency to use the improved 

 methods of hot water heating in very large ranges, and 

 that they are unquestionably more economical for small 

 houses. The greater durability of pipes constantly filled 

 with water is a strong point in favor of the hot water 

 system. 



Radiation required. The radiation required to heat a 

 house properly depends upon the exposure and the pro- 

 tection of the building, the area of glass exposed, the 

 temperature requirements of the crops grown, the 

 severity of the weather and the system of heating. 



One of the leading manufacturers of greenhouse boilers 

 uses the following data for finding the number of square 

 feet of pipe surface required to heat the house to various 

 temperatures with the gravity hot water system when the 

 outside temperature is zero : For 60 degrees to 65 degrees 

 divide square feet of glass and equivalent by 2.62 ; for 55 

 degrees to 60 degrees divide by 3; for 50 degrees to 55 

 degrees divide by 3.46 ; for 45 degrees to 50 degrees divide 

 by 4; for 40 degrees to 45 degrees divide by 4.67. Six 

 square feet of wall area should be figured as the equiva- 

 lent of one square foot of glass. The divisors named un- 

 doubtedly provide much more liberal radiation than is 

 common in most greenhouses which are devoted to vege- 

 table forcing, but it is better to have too much radiation 

 than not enough. Steam and the pressure systems of hot 

 water require less radiation. So many factors enter into 



