For years now I've been asked over an over about the vents on grills and how best to use them. So much so that I've decided to place a post on what the vents are for and whether they should be opened or closed during grilling. See our website for even for details as well as access to our great line up of products Jake's BBQ Sauces and Condiments.

With a gas grill, leave the lid closed at all times in order to maintain temperature. Gas grills work best with the lid closed during cooking, so that the heat circulates around the food.
Keep in mind that a windy day will make a charcoal grill a bit hotter (because it will oxygenate the coals), while a gas grill will run slightly cooler. Choosing a location that's sheltered from strong winds can help maintain grill temperature.
When cooking when is the best time to open the grill vents? Typically, the grill vents should be opened soon after the lid has been removed and the charcoals have reached their desired cooking temperature. Opening the vents allows air circulation which draws air through the bottom vents of the grill across the coals onto the meat and with heat rising upward through the top of the barbecue. With meats that are thicker and that require more time you want to sustain the heat levels necessary to cook the meat. A good idea is to leave the vents open between 1/4 and 1/2 of their total opening area. This will provide a reasonable amount of air necessary to retain the charcoals while they cook the meat without burning through the coals too quickly. For meats that can be grilled quickly and thus require a higher amount of heat open the vents wide open keeping in mind that charcoal will be burned at a higher rate and may require additional charcoal if more items are to be cooked later.
Always check to see that the vents are open on the bottom and top of the grill when using charcoal. If using gas keep the vents open just after lighting the grill then adjust the vents downward once the grill reaches desired temperature.
Mastering the vents can be done in 1-2 grill sessions but once you figure it out you'll find out how much fun it can be to perfectly adjust the vents for just the right grilling temperature.