Fired Heater

Know Which Heater is Right For Your Job Site: Direct or Indirect Fired Heater

Each year, many workers are killed by carbon monoxide poisoning. This is usually caused by fuel-burning equipment used in buildings or semi-enclosed spaces that lack adequate ventilation. However, without heat, winter outdoor workers as well as those who work in semi-enclosed spaces would be at risk of hypothermia or frostbite.

To combat the cold and protect workers from carbon monoxide poisoning, business owners and contractors need to understand the pros and cons of the two most commonly used mobile heaters.

Direct or indirect fired heaters are the most common type of heater used by contractors and business owners. Although both heaters heat the air and keep the workstations comfortable, they do not have the same purpose. Each type of heater has its own advantages and works better in different situations.


Direct-fired heaters are similar to gas grills where the flame comes into direct contact with the air. Direct-fired heaters, also known as salamander or torpedo heaters, are typically less expensive to operate than indirect fired heaters. They convert almost 100 percent of liquid propane and natural gas into usable heat.

Direct-fired heaters are smaller in footprint, easier to set up, move and adjust. However, due to their blower and open flame design, they cannot be used with ductwork. They are best used in large open areas such as warehouses, outdoor and indoor sports arenas, construction sites, and buildings with large open spaces.


Indirect fired heaters, on the other hand, operate as mobile furnaces and are more complex. These heaters are powered by oil, diesel, or propane and can draw fresh air from the outside through intake vents. The air passes through the burn chamber, where it is heated up and forced into buildings by blowers. The unwanted fumes from the heater are then expelled through a chimney. This process is safer than direct-fired heaters but can result in a loss of fuel efficiency.

Direct-fired heaters can be used to heat offices, factories, schools, and other facilities. No combustion byproducts are allowed into the airstream.


  • Indirect-fired heaters can be used to trap carbon monoxide and carbon dioxide in a space. They do this by directing toxic fumes through a chimney, stack, or other structure. They can be used indoors or in tight spaces, provided you have an exhaust outlet.
  • Direct-fired heaters can cause excessive humidity, which can lead to drying and curing problems, and even mold development in extreme cases.
  • Indirect-fired heaters are more efficient. Because they use drier air, these heaters speed up certain construction tasks, such as curing concrete.
  • Safety is always the first priority. Enclosed spaces that are not able to expel potentially dangerous fumes should be avoided. Direct-fired heaters can be a great choice for employees who work in well-ventilated areas.

No matter the season, safe and comfortable working conditions are essential. However, winter brings new challenges to contractors, business owners, and workers in the field. For more heating information, visit our site today.

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