Fan Cooling Test

I’ve suspected that the Bullet’s fan has a cooling effect on the roast. An interesting test may have confirmed this. Starting with a hot empty roaster running in a nearly steady condition with constant power P1, I increased the fan and watched the effect on temperature. Here’s what happened:

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Notice that as the fan is increased starting at 4:00 from F2 to F3 to F4, etc. the BT decreases more and more rapidly. Going back to F1 at 9:00 resulted in a positive RoR, but then longer 2 minute intervals of F2, F3, etc. again resulted in decreasing BT. So it looks like F1 may produce some heating, but F2 and above produce cooling.

This is unlike some other small gas roasters whose fan increases can have a pronounced heating effect. Good to know when comparing profiles and machine settings with other roasters.


I’m just a hobbyist, but this comes to no surprise to me. The fan pulls in ambient/cool air from a couple entrances and I would expect that air to absorb heat from the drum (thus cooling it slightly) - and I would also expect that the incoming warmed air isn’t as hot as the air that was sitting in the drum to begin with, so this slightly-warmed ‘cool’ air (relative to the original hot air) would cool/slow the roast.

I’m more surprised that increasing airflow on gas machines increases roast temperature… how does that work?

I think on gas roasters it pulls the air from the burner where the flame is so it would be hotter, and it helps the flame to burn better because of more air.