[header] How to preheat a convection oven [title] Read the oven's instruction manual. [step] Convection oven models are different and these steps may differ from the model that you own. Look for the owners or instruction manual that you got with your convection oven. 
If you don't have it, use a search engine to see if you can find an online version of the manual. [title] Press the convection button or turn the dial to convection.