Why a pellet grill's temperature swings up and down

A pellet grill doesn't hold one temperature the way a stove burner holds one flame. It chases the number you set, and chasing means drifting a little above it, then a little below it. That's the up-and-down.

What the swing actually is

Think of a home oven. The temperature wanders slightly around the setting, and the average is what cooks the food. One maker says its grill works the same way. The temperature will have slight fluctuations, higher or lower than the set temperature. Over time it averages out to what you set.¹

The difference is what you see. An oven shows you the average. A pellet grill's display shows the real-time number, so you watch every little rise and dip.¹

Why it happens at all

The grill can't dial a flame up or down smoothly. A motor-driven auger, which is a corkscrew, feeds a small amount of pellets from the hopper to the fire pot.² The pellets burn, the cooking chamber warms, and then the feeding stops for a while.

Between feeds, the grill is using up the heat it just made. When the temperature slips, the controller feeds more. That's a loop with a delay in it, and loops with delays overshoot and undershoot. The page on how the auger, fire pot and fan make heat walks through one full turn of that loop.

Low settings show the pattern clearly. At lower temperatures the auger sits idle for longer stretches, while at high temperatures the idle periods are shorter.²

How big is normal?

Makers give different numbers, and that's worth knowing. One maker puts its normal range at 15°F either way, on a typical day with good weather.¹ Another says its auger schedule will cause a swing of plus or minus 25 degrees, and calls temperature variation normal.³

So the range you'll hear is roughly 15 to 25 degrees. Which number applies to you depends on your grill. Your own manual is the one to trust.¹³

What can make it worse

The same maker lists several things that affect grill temperature: frequently opening the lid, cold weather, a heavy food load, poor airflow, and changing the set temperature often.¹

Each one is covered on its own page:

• Wind, cold and rain
• Opening the lid and recovery time
• Ash in the fire pot
• Pellets and the feed path

When it isn't normal

A swing that stays inside your maker's stated range, and averages out over the cook, is the grill doing its job. Trouble looks different: swings far bigger than the manual describes, a fire that keeps dropping out, or a display that disagrees badly with a second thermometer.

Those cases usually have a cause you can check. Start with the cheap, simple things like pellets and cleaning. If those don't help, the page on when swings point to a fault explains when to stop and contact the maker.