Construction heaters have many different fuel sources and designs to better serve the general contractors across the country. CHI Companies carries natural gas/propane heaters, water/steam heaters, electric heaters, boiler ground thaw heaters, and diesel heaters. The two major different designs of natural gas/propane heaters are categorized as direct-fired and indirect-fired.

Direct-Fired Heater: A direct-fired heater has the airflow go directly over the flame. Direct-fired heaters are usually smaller in size and can be placed either indoors or outdoors.

Indirect-Fired Heater: An indirect-fired heater has an heat exchanger that air passes over. Indirect-fired heaters are larger in size and will always be placed outdoor. The combustion byproducts are expelled through a stack on top of the unit. On average. 20% of the heat generated by an indirect-heater is expelled up the stack with the combustion byproducts. Example: An indirect-fired heater classified as 1,000,000 BTUH will only provide 800,000 BTUH into the project area.

Operating Costs: Direct-fired heaters are approximately half the daily rental cost of an indirect-fired heater. Fuel consumption of a direct-fired heater is identical to an indirect-fired heater, but the indirect-fired heater provides less heat. Therefore, the fuel operating expense is 20% higher with an indirect-fired heater.

Portability: Direct-fired heaters can be placed anywhere within a building creating even temperatures throughout the project. Indirect-fired heaters need to be placed outdoors to expel the combustion byproducts and will need ductwork to move the heat throughout the project.

Moisture: Direct-fired heaters will increase the moisture content into a project. On average, a direct-fired heater will increase relative humidity by 10% without drawing outside air and 3% while drawing outside air. An indirect-heater will not increase the relative humidity of the building. All moisture is expelled out the combustion stack.

Carbon Monoxide: Direct-fired heaters will introduce less than 1 ppm of carbon monoxide into a building, while an indirect-fired heater will not introduce any.