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Direct vs Indirect Fired Heaters

by Erik Hendricks 0 comments


Working outside during winter weather or other extreme conditions can be a challenge, especially when you’re at a construction site or a drafty manufacturing plant. Keeping buildings, tools and employees warm is vital to good work performance and helps achieve consistent, high-quality results. When it comes to choosing a heater for your situation, there are several things you’ll need to take into consideration.

Two Types of Heaters

There are two main choices of heater types for natural gas or propane heater rentals: direct fired and indirect fired heaters. Both types heat the air to keep the work area at a comfortable temperature. However, each heater works better in different situations and they both have distinct benefits.

Direct Fired Heaters

Direct fired heaters are similar to a gas grill where the flame comes into direct contact with the air. These heaters provide heat by forcing air through a gas flame. The direct heat transfer is incredibly efficient and allows the device to heat a space quickly while using minimal amounts of fuel. These portable heaters do produce CO2 emissions, so make sure to ventilate them properly.

Benefits of Direct Fired Heaters

Direct fired heaters are completely self-contained. This makes each unit relatively easy to move and adjust, saving you time and money in setup and installation procedures. Because they’re designed to be portable, these heaters are also relatively lightweight and can be adjusted to properly fit into the space you need to heat.

Most of the direct fired heaters offered by On Site Companies are also dual fuel heaters. This means they can be powered by either liquid propane or natural gas. This heater can switch fuel sources by swapping out regulators, which allows it to adjust when your job site changes.

The main benefit of direct fired heaters is that they are extremely efficient. Since the heat is produced by the flame coming in direct contact with the fuel source, the heaters will convert almost all fuel into usable heat.

If you don’t have electricity on your construction site, you could decide to rent a convection heater. Convection heaters are direct fired heaters that don’t have a blower or thermostat, so they don’t require electricity. The trade off with convection heaters is they aren’t as efficient as standard direct fired heaters since they are continuously running and don’t force warm air throughout your space.

The design of direct fired heaters focuses on simplicity. There are very few moving parts and maintenance requirements are minimal. You’ll be able to concentrate on getting the job done comfortably rather than worrying about fixing a heater throughout the day.

Direct fired heaters do create moisture, since the fuel comes in direct contact with the flame. If you can’t have ANY moisture produced from your heater, you might want to consider electric heaters or indirect fired heaters. However, if you just want to reduce moisture being produced by your direct fired heater, there are many ways you can properly ventilate your direct fired heaters to prevent moisture on your construction site.

Indirect Fired Heaters

Indirect fired heaters function like most home furnaces. Rather than sending air through a gas flame, the air is heated as it passes over an enclosed heating element. This keeps the air cleaner and reduces the amount of CO2 released by the heater. There is also no significant humidity added to the room, and the heater’s thermostat allows you to maintain a comfortable temperature without worrying about overheating the space.

Benefits of Indirect Fired Heaters

Indirect fired heaters are better for areas where people will be living or working. Because they do not add much CO2 into the air and reduce the risk of humidity buildup, you can use them in small indoor spaces. Even areas with poor ventilation (like small office areas and basements) can make use of indirect fired heaters without worrying about a change in air quality.

Indirect fired heaters are also self-contained, and the dryness of the heated air makes them perfect for heating rooms where mold is a concern. Best of all, these heaters can be used to heat multiple rooms at once with a simple network of ductwork to channel heat where it needs to go.

Indirect fired heaters are also useful in instances where noxious fumes are a concern. This would be areas such as living spaces, retail environments, and sewer jobs. The fumes created by indirect fired heaters will be safely vented away leaving you with no risk of exposure.

These heaters make use of an external exhaust system, keeping fumes from being released inside your space. An exhaust hose channels the fumes away from the heater and out a window or door, keeping you and your workers safe whenever the heater is in use.

The one downside of indirect fired heaters are their decreased fuel efficiency. Because of the manner in which heat is produced, not all fuel will be converted to usable heat.

Choosing the Right Heater

When trying to choose between a direct or indirect fired heater, there are a few things you should consider before making a decision. Going with the wrong heater can have serious safety consequences.

Consider the size of your space and the amount of ventilation the area has. If you’re working in a small and enclosed room, an indirect fired heater will work best. If you’re working in a large or well-ventilated space, a direct fired heater should be perfect.

Keep your budget in mind as well. The simplicity of direct fired heaters makes them more affordable than indirect fired heaters, and maintenance costs will be minimal. However, don’t try to cut costs by renting a direct fired heater when a space has poor ventilation. Safety should always come first.

Comfortable working conditions are a necessity. They improve morale, boost worker efficiency, and keep workers healthy & safe. Don’t settle for working in a cold room this winter. Rent a quality direct or indirect fired heater and see the difference warmth can make.

On Site Companies is a construction equipment rental company out of Minneapolis/St. Paul MN, Rochester MN, Mankato MN, and St. Louis MO. For more questions about renting heaters for your construction site, call us at 1.800.210.8407 or email us at

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