Hot air welder otherwise known as the hot gas welder is a kind of plastic welding technique which is almost similar to gas welding metals. However the specific technique is different in both the welding method. A hot air welder, which is a specially designed heat gun, produces a jet of hot air that softens both the parts to be joined and a plastic filler rod. It is important to note that all of the things to be welded must be of the same or a very similar plastic. However welding PVC to acrylic is an exception to this rule. For manufacturing smaller items like chemical tanks, water tanks, heat exchangers and plumbing fittings, the hot air welder is the most common fabrication technique being used.

If the welder is used to weld case of webs and films, a filler rod may not be used. Here two sheets of plastic would be heated using a hot gas or a heating element and then rolled together. This process is comparatively fast and can be accomplished continuously. There is another variation in the hot sir welding technique. It is called the freehand welding in which the jet of hot air from the welder is played on the weld area and the tip of the weld rod simultaneously. The rod is pushed into the joint and fuses to the parts as it softens. This process is slower compared to others. But the welding is versatile and can be used in almost any situation.