Although the saddle boiler existed in many forms, all were variations on the basic design of using a flat surface against the furnace as the method of heating the water. Enhancements were made to the basic design by various ingenious techniques, such as corrugating the surface, so as increasing the surface area adjacent to the furnace or by utilising secondary heating techniques by subdividing and multiplying the flues. The reasons these boilers became so popular was their efficiency, ease of use and reliability.
Typically saddle boilers were made of wrought iron, although occasionally cast-iron was used especially those that used a number of longitudinal internal flues. However, cast iron was not as resistant to corrosion, incrustation or high pressure as wrought iron.
Saddle boilers were produced in various sizes, typically ranging from 2ft. to 5ft. in length. The heating power was obviously dependent upon size, for example a two-foot long flue and terminal end saddle boiler was claimed to be capable of heating 500 feet. of 4-inch pipe; whilst a three-foot long boiler could heat 800 feet and a five-foot long boiler 2,000 feet.
At the 1872 Royal Horticultural Society’s Birmingham exhibition, Mr. Frederick Mee of Smithdown Road, Liverpool displayed three modified saddle boilers, entering one of them into the ill-fated boiler competition. This was a three-foot long double saddle boiler, whereby one wrought iron saddle sits directly above another. The two saddles were welded together and connected with a front soleplate, wrought-iron tubular fire-bars, and a hollow terminal back. This allowed for independent circulation, either working in conjunction with the boiler or independently.
The firm were selling saddle boilers as early as 1882, when they were offering two saddle boilers, one an improved saddle boiler and the other the Chatsworth.
The improved saddle boiler had a terminal end, which greatly improved its heating power and was recommended for heating pipes between 100 and 500 feet in length. The sold it in ten modcels, ranging in size from 24in. x 14in. 14in. (L x W x H) upto 42in. x 18in. x 18in. and capable of heating from 500 feet (No. 1) to 1,100 feet (No. 10) of pipe.
The Chatsworth boiler had both a terminal end and a return flue through the crown and was recommended for heating lengths of pipe between 800 to 2,000 feet. It exposed a very large surface area, including the sides of the boiler and with a large internal flue it was unlikely to become blocked with soot. The boiler was also available with a top feed enabling it to be fed with enough fuel to last throughout the night. The firm offered the boiler in eighteen models, ranging in size from 18in. (length) x 12in. (width) x 10in. (high) upto 54in. x 21in. 21in. and capable of heating between 300 and 2,000 of high-pressure 4in. pipes.
Into the twentieth century and upto World War Two, the firm was offering three wrought iron welded saddle boilers, the No. 52, a plain saddle boiler, the No. 54, a saddle boiler with a waterway check end and No. 61, the Chatsworth.
The No. 52 boiler was offered in eighteen models and all available in two gauges of plate, 5/16in. thick and ⅜in. thick The smallest measuring 18in. (length) x 12in. (inside arch width) x 12in. (inside arch height) was capable of heating upto 180 feet of 4-inch pipes, providing 210 square feet of radiation and rate at 31,000 B.T.U. per hour. The largest boiler measuring 72in. (length) x 24in. (inside arch width) x 21in. (inside arch height) was capable of heating upto 1,360 feet of 4-inch pipes, providing 1,632 square feet of radiation and rated at 235,000 B.T.U. per hour.
The No 54 boiler was offered in seventeen models and again in two gauges of plate, 5/16in. and ⅜in.; the 5/16in plate was only available in the first thirteen of the eighteen sizes, whilst the ⅜in. thick plate boilers was available across the whole range. The smallest boiler measured 18in. (length) x 12in. (inside arch width) x 12in. (inside arch height) and was capable of heating upto 180 feet of 4-inch pipes, providing 210 square feet of radiation and rate at 31,000 B.T.U. per hour. The largest boiler measured 84in. (length) x 36in. (inside arch width) x 24in. (inside arch height) and capable of heating upto 2,150 feet of 4-inch pipes, providing 2,580 square feet of radiation and rated at 382,520 B.T.U. per hour.
The Chatsworth was offered in almost sixty variants, twenty nine different sizes and in two thicknesses of plate 5/16in. and ⅜in. The smallest boiler, capable of heating 240ft. of 4inch pipes, measured 18 inches in length, 12 inches (inside arch width), 10 inches (inside arch height), 17 inches (outside arch width) and 18 inches (outside arch height). The largest, capable of heating 2,350ft. of 4-inch pipes, measured 84 inches in length, 30 inches (inside arch width), 21 inches (inside arch height), 38 inches (outside arch width) and 32 inches (outside arch height). The size 3 boiler (measuring 24in. 14in. 14in., 20in. and 25in. respectively) was capable of heating 375 feet of 4-inch pipes providing 450 square feet of radiation and rated at 64,500 B.T.U. per hour. The No. 26 boiler (measuring 72in, 30in., 21in., 38in. and 32in. respectively) was capable of heating 2,025 feet of 4-inch pipes providing 2,430 square feet of radiation and rated at 348,300 B.T.U. per hour. To help avoid errors when ordering, each boiler was assigned a code word, in this instance beginning with a ‘C’. Thus the customer was only expected to provide the key word (Chat, Chabis, Chace, Chad, Chaffy, etc.), plate thickness and any fitting required.