An indirect fired heater burns fuel in a sealed combustion chamber and blows clean, dry air into your work area. The flame and exhaust never touch the air your crew breathes, which makes it the standard and a common choice for heating hoarding, tents, and buildings under construction across Northern Alberta and Northeast BC.
But “standard” doesn’t mean cheapest to run. This guide explains how indirect fired heaters work, what they burn in a winter day, and when a flameless heater does the same job with less fuel and fewer trips to site.
What is an indirect fired heater?
An indirect-fired heater is a portable heater that keeps the flame and the heated air apart. Fuel burns inside a combustion chamber. A heat exchanger passes that heat to fresh air, and a fan pushes the warm air through ducting into the space. The exhaust leaves through a separate flue.
Most units on Canadian jobsites burn diesel, propane or natural gas. They’re used for:
- Heated hoarding and temporary enclosures
- Buildings under construction with no permanent heat yet
- Concrete curing and ground thaw under tarps
- Wellheads, BOPs and rig floors in the oilfield
- Warm-up shelters for crews
How an indirect fired heater works:
- Fuel burns in a sealed combustion chamber. A burner fires diesel, propane or natural gas.
- The heat exchanger gets hot. Combustion gases pass through it and heat its metal walls.
- A fan blows air across the heat exchanger. That air warms up without ever touching the flame or exhaust.
- Warm air goes into the space through ducting. You can place the heater outside and run duct into the hoarding.
- Exhaust leaves through the flue. Combustion gases are vented outside, away from the heated air.
Because some heat leaves with the exhaust, an indirect fired heater uses more fuel than the same heat from a direct-fired unit. You’re paying for clean air.
Indirect vs direct fired heaters
| Direct fired | Indirect fired | |
|---|---|---|
| Where the flame is | In the airstream | In a sealed chamber |
| Exhaust | Goes into the heated space | Vented outside through a flue |
| Air quality | Adds carbon monoxide, CO₂ and moisture | Heated air without combustion exhaust |
| Fuel use | Less fuel for the same heat | More fuel (heat lost up the flue) |
| Best for | Well-ventilated, open areas | Enclosed and occupied spaces |
Direct fired heaters put moisture into the air, which slows drywall, paint and concrete curing. In an enclosed space with crews inside, an indirect or flameless heater is the safer choice.
What indirect-fired heaters burn in a day
Fuel use depends on the unit’s size and how hard it runs. Most diesel indirect fired heaters on Northern jobsites need refuelling at least once a day in deep cold.
The BASECAMP manufacturer’s comparison of a traditional indirect flamed heater, running on high, gives:
- Fuel: about 300 litres per unit in 24 hours
- Run time on a tank: about 12 hours on high
- Power: needs an external generator to run
That’s before you count the generator’s own fuel, and the light tower most sites run beside it.
Where indirect fired heaters fall short in a northern winter
Indirect fired heaters work. The cost shows up around them:
- Fuel trips. At −30°C or colder, a 12-hour run time means someone drives to site to refuel, often on winter roads, often at night.
- Extra equipment. One indirect heater usually means a generator to power it and a light tower for short winter days. That’s three units to rent, fuel and check.
- Several units for big spaces. Large hoarding or multi-storey buildings often need two or three heaters.
- A flame on site. Many sites require a fire watch for flame-fired heaters, which means paying someone to watch the equipment.
- No eyes on it at night. If a heater stops at 2 a.m., you usually find out at 7 a.m., when the concrete or wellhead is already cold.
Flameless heaters: how they’re different
A flameless heater makes heat without a burner. Most use a diesel engine: the engine drives a heat generator and its own waste heat is captured too. A fan sends the heat through ducting, just like an indirect fired heater. There’s no open flame and no combustion in the heated air.
BASECAMP, the flameless heater Nakoda rents, also builds in a light tower and a generator, so one unit covers heat, light and power on site.
Indirect fired vs flameless: side by side
Figures from the BASECAMP manufacturer’s comparison, per unit, running on high:
| Measurement | Traditional indirect fired heater | BASECAMP flameless heater |
|---|---|---|
| Units for the same heat | 2-2.5 | 1 |
| Heating method | Fuel burns in a sealed combustion chamber; heat exchanger warms clean air | Diesel engine and heat-recovery system; no open-flame burner in the heated airstream |
| Run time on high | About 12 hours on a tank, depending on unit and load | Up to 48 hours of continuous runtime |
| Open flame | Yes | No open-flame burner in the heated airstream |
| Needs an external generator | Yes | No, BASECAMP has a built in generator (27–40 kW built in) |
| Built-in light tower | Usually rented separately | Yes (192,000–230,000 lumens) |
| Ducting reach | Shorter runs | Up to 250 ft |
| Remote monitoring | No | Yes BASECAMP heater can be monitored remotely via SmartTalk, 24/7 alerts |
Put simply: one BASECAMP does the heating work of two and a half indirect-fired heaters, on about 60% less fuel, and runs three times as long between refills.
Which one should you use?
An indirect fired heater makes sense when:
- The job is short (a few days)
- You already have site power and easy fuel delivery
- The space is small enough for one unit
A flameless heater makes more sense when:
- The site is remote, and every fuel trip costs hours
- Crews work inside the heated space
- You’d otherwise rent a heater, a generator and a light tower separately
- You need to know the heater is still running overnight
- The job runs weeks or months, so fuel savings add up
How big a heater do you need?
Size depends on the volume of the space, how well it’s insulated, how leaky it is, and how cold it gets outside. Use our BTU calculator to get your heating load in BTU/hr, then compare it with BASECAMP’s 700,000 to 1,000,000 BTU equivalent output. For more on sizing, read How Many BTUs Do You Need to Heat Your Construction Site?
Frequently asked questions
- What is an indirect fired heater? A portable heater that burns fuel in a sealed chamber and uses a heat exchanger to warm clean air. The exhaust is vented outside, so the heated air has no combustion fumes.
- What’s the difference between direct and indirect-fired heaters? A direct-fired heater puts the flame and its exhaust straight into the heated air. An indirect fired heater keeps them separate and vents the exhaust outside. Direct is more fuel-efficient; indirect gives clean, dry air.
- Is an indirect fired heater safe in an enclosed space? It’s much safer than a direct-fired heater, because the exhaust is vented outside. Keep the exhaust away from air intakes and openings, inspect the heat exchanger for cracks, and use a CO monitor. Follow your site’s safety rules.
- How much diesel does an indirect fired heater use? It depends on size and output. The BASECAMP manufacturer’s comparison puts a traditional indirect flamed heater at about 300 litres in 24 hours on high, with a 12-hour run time on a tank.
- Do indirect fired heaters need a generator? Most do. The fan and burner need electrical power. On sites without power, that means renting and fuelling a generator too.
- What is a flameless heater? A flameless heater makes heat without a burner. Most use a diesel engine: the engine drives a heat generator and its own waste heat is captured too. A fan sends the heat through ducting, just like an indirect fired heater. There’s no open flame and no combustion in the heated air.
- How does a flameless heater work? A diesel engine drives a heat generator, and the engine’s own heat is captured as well. A fan pushes the warm air through ducting into the space.
Heating a site this winter? Nakoda rents BASECAMP flameless heaters across Northern Alberta and Northeast BC, from Grande Prairie and Fort St. John. Every unit comes with 24/7 monitoring and dispatch support. Industrial heater rental in Grande Prairie or call 1-855-745-7902.
