It appears that Thomas Messenger started developing, manufacturing and installing his triangular boiler prior to moving into developing his greenhouse and horticultural business. Presumably, he realised the potential for such a boiler for more general heating solutions, such as churches, factories, public buildings, workshops, hotels, etc. The firm probably initially bought in some if not all of the components such as boilers, piping, valves and coil radiators. However, they later went onto manufacture their own boilers and valves, if not all the rest of the components.
When Thomas Messenger began, the saddle boiler was regarded as a good general-purpose boiler and it is essentially this design that Thomas Messenger used in developing his horizontal triangular tubular boiler. Boiler design developed so as to bring the largest surface area in contact the flame. The flip side to this was the fact that if the design became too convoluted in order to maximise the surface area, not only would the flow of water be reduced which could be dangerous, but the flue gases had to escape safely and easily otherwise they would choke the fire.
The objective was to develop a boiler that provided the required water temperature with the maximum efficiency (i.e. used the least amount of fuel), with minimal effort (i.e. did not require constant attention – stoking, raking out, etc.) and was reliable.