174 FIXED STRUCTURES FOR GROWING 



calculating the loss of heat from exposed surfaces of glass under dif- 

 ferent circumstances and situations, Mr. Hood gives the following 

 rules for determining the quantity of pipe as a sufficient approxima- 

 tion for ordinary purposes : " In churches and very large public 

 rooms, which have only about an average number of doors and 

 windows, and moderate ventilation, by taking the cubic measurement 

 of the room, and dividing the number thus obtained by 200, the 

 quotient will be the number of feet in length of pipe, four inches in 

 diameter, which will be required to obtain a temperature of about 

 55 to 58. For smaller rooms, dwelling-houses, &c., the cubic 

 measurement should be divided by 150, which will give the number 

 of feet of four-inch pipe. For greenhouses, conservatories, and such- 

 like buildings, where the temperature is required to be kept at about 

 60, dividing the cubic measurement of the building by 30 will give 

 the required quantity of pipe : and for forcing-houses, where it is 

 desired to keep the temperature at 70 to 75, we must divide the 

 cubic measurement of the house by 20 ; but if the temperature be 

 required as high as 75 to 80, then we must divide by 18 to obtain 

 the number of feet of four-inch pipe. If the pipes are to be three 

 inches diameter, then we must add one-third to the quantity thus 

 obtained ; and if two-inch pipes are to be used, we must take double 

 the length of four-inch pipe. 



"The quantity of pipe estimated in this way will only suit for such 

 places as are built quite on the usual plan/' (' Treatise,' &c., p. 125.) 

 The above calculations for heating are made on the supposition that 

 the lowest external temperature will be 10 ; but in situations 

 " exposed to high winds, it will be prudent," Mr. Hood observes, " to 

 calculate the external temperature from zero, or even below that, 

 according to circumstances ; and in very warm and sheltered situa- 

 tions, a less range in the temperature will be sufficient." Local cir- 

 cumstances, therefore, may require from 5 to 10 per cent, to be 

 added to, or deducted from, the length of pipe found according to 

 the foregoing rules. As a proof of the soundness of Mr. Hood's 

 calculation, we may state that the great stove at Chatsworth is heated 

 at the rate of one superficial foot of heated pipe to thirty cubic 

 feet of air ; and the temperature kept up during the severest 

 weather of the winter of 1840-41 was 60, though there were fre- 

 quently from 20 to 35 of frost during the night. This house is sixty 

 feet high, with glass on all sides, exposing a surface of 60,000 feet, and 

 enclosing 1,050,000 cubic feet of air. The quantity of coal consumed 

 was about two tons per night. (' Gard. Chron.,' April 17, 1841, p. 243.) 



The situation in which the pipes are placed is, in general, what we 

 have stated to be the most suitable for smoke-flues (p. 165) viz., along 

 the front and ends of houses placed against a back wall, and entirely 

 round detached or span-roofed houses. In the case of pits or frames 

 with flat roofs, the pipes may be either placed in front or in the middle, 

 always bearing in mind that heated air ascends, and that the quantity 

 heated in a given time will, all other circumstances being alike, depend 

 on a regular supply to the heating body, by a current distinct from 



