CONSTRUCTION OF GARDEN WALLS. 



87 



for conveying the smoke and heated air 

 that passes the boiler along them, for the 

 purpose of economising the heat which 

 would otherwise escape at the chimney top 

 — the great dependence being on the heat 

 from the water to effect the end in view. 



The best flued walls we have seen are 

 those exemplified in the garden at Erskine 



House. These were described by Mr Shiells, 

 the very intelligent gardener there, in the 

 " Gardeners' Magazine," (vol. iii. p. 670,) 

 accompanied with the annexed diagram, 

 fig. 78 : " Our mode of heating these 

 walls," says the author, "is simple but 

 effectual. As will be seen" by the illus- 

 tration, " there is an open space, with a 



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damper placed immediately over it, where 

 the smoke and heated air enter the wall 

 from the furnace at a ; this damper re- 

 gulates the heat through the whole wall. 

 I found, when the damper was drawn 

 about 4 inches, a sufficient portion of the 

 smoke and heated air passed through the 

 two under flues to produce the necessary 

 degree of heat in these flues ; and, after 

 passing through these, being again united 

 to that part ascending through the open- 

 ing left at a, the whole body of smoke 

 then ascends, and passes through the 

 third and upper flues, by which these 

 are heated a little more than the lower 

 ones. This" Mr Shiells "considers a 

 great advantage, because the upper part 

 of the wall is more exposed to the cold 

 air, and less benefited by the reflection of 

 heat from the ground; besides, the shoots 

 there are generally more luxuriant and 

 spongy, and consequently later in ripen- 

 ing. No trellis is required for this wall ; 

 for, if the damper be properly fixed, there 

 is no danger of overheating any part of 

 it; the only part where danger from 

 overheating is to be apprehended is where 

 the heat enters from the furnace, which 

 is 18 inches from the wall, and 2 feet 

 below the surface of the ground. To 

 prevent the roots of the trees on the 

 south side of the wall from being injured 

 by the heat, 4-inch brickwork is carried 

 up, opposite the furnace, to within a few 

 inches of the surface, with a 2-inch cavity 

 h. As the heat rises above the surface, 



0 lu 20 30 ft. 



it enters the wide space c, from whence it 

 is immediately directed through the wall. 



1 have," Mr Shiells observes, "however, 

 a yard or two of the wall, at the warm 

 end of the under flues, a little thicker, d, 

 as flued walls are always warmest towards 

 the top of the flues." The idea struck 

 Mr Shiells, " that if one, two, or more 

 bricks (according to the depth of the flues) 

 were built across the upper ends, they 

 would, by confining the draught of smoke 

 towards the bottom of the flues, tend to 

 equalise the heat in them. This did not 

 answer" his expectation, " for it retained 

 too much of the heat in the under and 

 third flues, which caused a deficiency in 

 the second and upper ones ; but having 

 bricks run across the upper part of the 

 cooler ends of the second and upper flues 

 is of considerable advantage, as a means 

 of retaining the heat in these flues, and 

 making the heat throughout more equal 

 and uniform, and requiring less fire ; in- 

 deed, walls upon this construction never 

 require large fires. 



" If it were desirable to warm the 

 upper part of the wall only, by withdraw- 

 ing the damper, and applying a small 

 fire, this would be accomplished without 

 warming the lower part of the wall. 

 Depth of flues, 2 feet 6 inches, 2 feet, 

 2 feet 3 inches, and 1 foot 6 inches; 

 width, 1\ inches; bottom of lowest under 

 flue, 1 foot from the surface ; top of upper 

 flue, 7 inches from the coping; thickness 

 of the wall, about 1 foot 9 inches. By 



