Boilers typically come in either a fire-tube or water-tube heating design and they are designed either to run on natural gas or a dual-fuel option. Fire-tube vs. Water-tube. Most conventional boilers use a fire-tube design in which hot flue gas runs through a tube that is surrounded by the water in the tank.
Air heating in construction sector. A specific application of Direct Fired Heaters which although it involves specific design is not very sophisticated as its configuration is very different to that shown in Fig.1 is that of heating for drying or heating in construction works see Fig 3-.
Industrial Hot Water Boilers follow a relatively similar design concept to Steam Boilers in many respects although they are completely filled with water during operation whereas Steam Boilers operate with a water level and steam space. A burner fires into the boiler furnace and tubes to heat the water inside the boiler