Convection ovens cook faster and more evenly than traditional ovens, which means that you need to adjust the time and temperature called for in traditional recipes.
A traditional oven has one, or sometimes two, heating elements, usually located at the top and bottom of the cooking area. Heat waves bounce off the walls of the oven causing the overall temperature to rise.
Convection ovens add a fan and often a third heating element to the traditional oven design. The fan circulates hot air evenly throughout the oven resulting in faster, more even cooking. Moving air transfers heat more efficiently than still air. This means that food cooks more quickly in a convection oven than it does in a traditional one. It also means that foods brown more quickly and more evenly than they would in a traditional oven. This eliminates the need for rotating the roast halfway through the cooking time, although you will still need to flip it so the underside browns.
If you have a traditional oven with a convection setting, try using it for the first 15 minutes of cooking time. This will give you the browning benefits of convection, without having to adjust your recipe.
Use the rule of 25 when adjusting recipes designed for a traditional oven: Reduce the temperature by 25 degrees Fahrenheit and reduce the cook time by 25 percent. For example:
Cook a 3-pound pork roast at 325 F for 45 to 55 minutes, or until it reaches at least 145 F.
A 5-pound whole chicken can roast at 350 F for 1 hour and 20 minutes, or until it reaches an internal temperature of 165 F.
Roast an 8-pound beef rib-eye at 325 F for 2 hours, or until the internal temperature reaches 145 F.
The exact time required to cook a specific roast will vary depending on the size of the roast, the type of meat and whether it is boneless or bone-in. Use these guidelines as a starting point, but always use the internal temperature to determine if the roast is done.