Hey, does room temperature play a role in preheating? I have 16°C (60.8 F) in my basement.
Preheat is the only temp control action in the Bullet so it should be relatively independent of room ambient. Of more concern during Preheat is the IR sensor in IBTS. Roast-contamination of the sensor window (the “lens”) blocks some of the IR and causes an error. Depending on how dark you roast and how long you wait to clean the sensor surface you can accumulate a sizeable error. The result is that a dirty sensor window will cause the Bullet to Preheat to a higher temp than what you set as target with either f/w or a Recipe.
Room ambient will affect power settings during the roast but I can’t begin to quantify that for you. Using Recipes and adjusting P/D/F settings in the Recipe based upon temp readings can probably eliminate the thermal losses/gains from your room environment. You’ll have to decide for yourself if all the development time is worth it, especially since changing to a different bean will change the needed thermal profile & the Recipe adjustments.