lO Heating Grecn-hoicses. 



from the furnace with a good degree of facihty, and carries it off to be 

 radiated in the house. Still, it is true that, with our most popular boil- 

 ers, the smoke flue continues to be quite hot when the direct draft is on, 

 and there is still a consequent large waste up chimney. The only rem- 

 ed}' for this evil in the ordinary iron boilers of the day, and a partial 

 remedy at best, is this — to continue the horizontal flue, in combination 

 with the water, in order to economize the largest amount of heat. 



Looking back to the hot-air, or Polmaise, system, we can see that 

 there is no necessity for the heavy brick furnace. Instead of it, cover 

 the fire with a dome or arch of thin iron ; then surround the dome with 

 an air-chamber, through which a large and rapid current of cold air 

 becomes heated as it passes from the bottom up into and through the 

 house. If the metal is thin, and the circulation is large and rapid, I 

 am convinced that a large percentage of the caloric is radiated and 

 carried off into the house. The current of air may be made so large 

 and so rapid as to prevent the tendency to overheat the iron or burn the 

 air. For some positions, and especially for hill-side houses, I believe a 

 form of hot-air furnace is the most economical and the best that can be 

 devised. 



Thinness of material is a point to which allusion has been made, and 

 it is an important point. If we must cover our fire, in order to carry 

 off the smoke and gases, let us do it with the thinnest material possible 

 and attain our end. By so doing we shall obtain the largest percentage 

 of heat. It is well understood by scientific engineers that steam is more 

 easily generated in steel boilers than in the ordinary iron boiler, and the 

 thinner the plate the greater the ease. Bring the water as nearly in 

 contact with the fire as is consistent with strength, reduce the amount 

 of rust and soot to a minimum, and, beyond question, we shall extract 

 the maximum of caloric from the fire. In this view, it seems that cop- 

 per would be an excellent material for boilers. In practice, it is found 

 to work admirably for small houses, and with great economy of fuel. 

 There are, however, some practical difficulties in the construction of 

 large boilers of copper, and, in order to give sufficient strength, the 

 weight of metal will involve high cost. Still, it may prove to be cheap- 

 est in the end. Whatever the material or the form may be, whether 

 hot water, steam, or hot air, obsei^ve always to cover the fire with the 

 thinnest and most perfect conductor of heat, consistent with strength 

 and cost. 



