A blowlamp is a simple heating torch, which burns fuel with ambient atmospheric air. It will typically run on propane or butane cartridges, or be fed from a liquid petroleum gas cylinder via a hose. They produce a much larger, softer flame than an oxyacetylene torch and are used for low temperature applications - soldering, brazing, melting roof tar, or pre-heating large castings before welding, such as for repairing cast-iron cylinder heads.