How the auger, fire pot and fan make heat

Four parts make nearly all the heat in a pellet grill: a hopper, an auger, a fire pot and a fan. Once you know what each one does, the temperature swings stop looking mysterious.

The parts, in the order a pellet meets them

Pellets sit in the hopper, a storage box. When the grill starts, an auger begins to pull pellets from the hopper down into a fire pot.¹ The auger is a corkscrew turned by an electric motor.²

The fire pot is where the pellets burn. At startup, an igniter rod lights the pellets and primes the fire.³ Once the pellets are burning, the ignition rod shuts off.¹

The fan does two jobs. It forces air across the fire pot, and it circulates heat and smoke through the cooking chamber while giving the pellets oxygen.¹ Fire needs air as much as fuel. Some grills use one fan, some use more.¹

Where the cycle comes from

Early pellet grills ran the auger at a set speed. The slower the speed, the lower the temperature, and the other way round.¹ Modern grills still lean on the same idea, only with a smarter brain on top.

Here's the key. Once the fire is going, the grill reaches your setting through a repeated duty cycle. That's a stretch when the auger runs, then a stretch when it's idle.³ The same source says duty cycles are typically stated as a percentage. An auger that ran all the time would be at 100 percent.³

Lower temperatures have longer auger-off periods, and higher temperatures have shorter ones.³

Why that makes a wave

Picture one turn of the loop.

A burst of pellets lands in the pot. They take a little while to catch and burn, so heat builds after the auger has already stopped. Then the grill spends that heat on the cooking chamber, the food and the outside air. When the chamber cools below the target, the controller starts the auger again.

Burning fuel isn't instant and neither is cooling. Because of that delay, the temperature rarely sits still, and it rolls up and down around the target as the grill catches up with itself. The wave is built in.

What this means when you cook

A few practical points follow from the mechanism.

• A grill that has just started is still building its fire. Give it time before judging the numbers.
• Anything that changes how much heat the grill loses will change how often it feeds. Weather and the lid do this, and they get their own pages: weather and lid opening.
• Anything that disturbs fuel or air, such as ash, damp pellets or a blocked fan, changes the fire itself. See how ash upsets the fire and what goes wrong with pellets.

How the controller decides when to start the auger is the next piece. It's covered in how the controller and sensor decide when to feed.

Parts and start-up steps differ between models, so follow your own manual for startup and shutdown.