December 9, 18G9. ] 



JOURNAL OF HORTICULTURE AND COTTAGE GARDESEK. 



45£ 



HEATING BY HOT-WATER PIPES. 



IK^BS^ ERHAPS in the long Ust of liortioultural 

 means and appendages, none are so little 

 understood as the theory and practice of 

 heating by hot water, nor any of them sur- 

 rounded by so much mystery : yet the sub- 

 ject is so simple, and requires so little time 

 to master it, that no lady or gentleman should 

 be ignorant on this point or liable to be im- 

 posed upon. 



Very few indeed understand why the water 

 circulates in the pipes, the prevalent idea being that the 

 fire drives the water out of the boiler with great force. 

 Such is not the case, the circulation of water is always 

 comparatively weak. The force it possesses is only equiva- 

 lent to the difterence in weight between the ascending and 

 descending column of water. Hot water is lighter than 

 cold : therefore when the fire is applied to the boiler the 

 water in it becomes hotter and lighter than that in the 

 pipes attached to it, consequently it ascends, and its place 

 is supplied by the water in the pipes, which is cold and 

 heavier. The pipes being liigher tlian the boiler, the 

 water descends into it. This goes on till the whole of the 

 water in the apparatus becomes comparatively warm. Of 

 course the water is hottest in the boiler, hot in the flow 

 pipe, and cooler in the return. What I mean by this is 

 that the water is gradually cooled as it leaves the boiler 

 by the heat being absorbed from it by the action of the 

 air on the surface of the pipes. Thus the force of the 

 cm-rent corresponds to the cUiference between the boiler 

 and the return pipe in the temperature and specific gravity 

 of the water. The force is easily calculated, but it would 

 not be interesting to go into details of this kind ; let it be 

 snlficient to say I believe the average force in a 4-inch 

 pipe as usually laid in a greenhouse is only equal to about 

 one- third of an ounce. This tells us we must so place the 

 pipes as to ati'ord no resistance to the current — that is, we 

 must have no sharp turns nor irregular depressions, espe- 

 cially in the return pipe, which should always have an 

 even descending course. 



When about to construct a warming apparatus, the first 

 point is to decide upon the kind of pipes we shall use — that 

 is. Should they be large or smaU ? Small pipes become hot 

 the quickest, present more heating surface in proportion to 

 the water they contain, require less fuel, and become cold 

 quicker than those of larger diameter. They are more 

 portable, and far more expensive. Pipes of large diameter 

 do not present so great a heating surface in proportion to 

 their cubic contents, but they keep hot longer after the 

 fire is out, and are cheaper, and perhaps more suitable to 

 greenhouses. 



To make this clear, a -i-inch pipe contains in each foot 

 of length nearly 14(i cubic inches of water, and presents 

 about 14i inches of heating surface; a -I -inch pipe con- 

 tains in each foot of length nearly On inches of water, and 

 presents "ii inches of surface : therefore one row of 4 inch 

 pipes gives oft' as much heat as two rows of 2-inch pipes, 

 but contains nearly double the quantity of water and re- 



Ko. 454.— Vol" ^VII.,New Sekies. 



quires double the quantity of fuel to keep up the heat — that 

 is, the two rows of 2-inch pipe are equal in warming power 

 to the one row of 4-inoh, and superior to it in economy. 



Having decided on the diameter of the pipes, we nest 

 require to know the quantity we shall want to keep a 

 certain house warm. This is done by proportioning the 

 surface presented by the pipes to the surface presented by 

 the glass : for so great is the cooling power of the glass 

 that it puts the cubic contents of the house out of the 

 calculation. Therefore we only require to know how much 

 air a foot of glass will cool down from a certain tempe- 

 rature to a lower one. and the quantity of air a foot of 

 heating surface will raise in temperature in the same 

 (opposite) way. However, it would, I fear, make my paper 

 too long if I were to go into this matter scientifically : so I 

 will give a rule for calculating the quantity of pipes re- 

 quired to heat any building of the hortioultui-al class. 



Decide upon the heat you require in the house whea 

 the temperature of the external air is at the lowest point. 

 The quantity of air to be warmed per minute is 1.'; cubic 

 foot for each foot superficial of glass the house contains. 

 When the quantity of air to be heated per minute has 

 been decided upon, multiply 12.i (the excess of the tem- 

 perature of the pipe above that of the surrounding air), 

 by the diflerence of the temperature at which it is proposed 

 to keep the house above that of the external air, and 

 divide this product by the difference between the tempe- 

 rature of the pipes and the proposed temperature of the 

 house ; then the quotient multiplied by the number of 

 feet of air to be warmed, and this product divided by 

 222 (the number of feet of air raised 1° per minute by 1 foot 

 of 4-inch pipe), will give the number of feet of 4-inch pipe 

 required to produce the desired effect. 



Now, wo want to know how large a boilter we require to 

 heat the water to supply the pipes. For each 50 feet of 

 iinch pipe, tlie boiler must present one square foot of 

 sui-face to the dkeot action of the fire : so if the house 

 contains 200 feet of pipe, a boiler wiU be requu-ed that 

 presents 4 feet of surface to the fire. Never count any- 

 thing for the surface exposed to the action of flame upon 

 the top of it, such as the top of any boiler, for the fire wouM 

 nover have power enough to boU water underneath it. 



I have now stated enough to enable ladies or gentle- 

 men to know which pipes will suit their purpose the 

 best, how many feet of piping they will require, and the 

 size of boiler necessary to heat the water. If they will 

 only rely on their ovnx judgment, and follow the teach- 

 ings of science, they will not be so frequently disappointed 

 in the warming of their horticultaral houses. — Johs 

 Wooi.iiELD, Soho, Dirminijhiti:>. 



GUERNSEY CHRYSANTHEMUMS. 

 Guernsey seedlings of this popular and useful flower — 

 not that I personally like or admire it. considering it muck 

 overpraised — have become so weU known to English shotrg, 

 and have so good a place in Messrs Salter's list, that these 

 brief notes of mine taken at an insular exhibition may add 

 to the interest felt in them. Guercssy holding just new four 

 lio. 1106.- Vol. xm., Old Sfjum. 



