A gas heateris a space heaterused to heat a room or outdoor area by burning natural gas, liquefied petroleum gas, propaneor butane. Indoor household gas heaters can be broadly categorized in one of two ways: fluedor non-flued,or ventedand unvented.

Heaters used in industry for steam generation and petroleum refining are known as fired heater, process heaters, furnaces or process furnaces. Fired heaters are used throughout hydrocarbon and chemical processing industries such as refineries, gas plants, petrochemicals, chemicals and synthetics, olefins, ammonia and fertilizer plants.

In the oil and gas segment, fired heaters are essential for heating - thermic fluids, process fluids, feedstock, charge heating, steam heating and thermal cracking in the refinery segment. The design of these units depends on the application and the choice between 'vertical cylindrical' or 'box-type furnace' designs.

Fired heaters, or process heaters, are important to refineries and petrochemical plants because they heat and vaporize the hydrocarbon fluids to create necessities like gasoline, diesel, and jet fuel. As of January 2019, there are 135 petroleum refineries in the US.