An old cleaning method for a dirty gas grill was to cover the cooking grates with aluminum foil, turn the grill to high for 20 minutes, let it cool, and then simply brush off the ash. The foil holds the heat from the gas burners under the grates and reduces virtually everything to a fine dry ash that can be easily cleaned up.
Negative Impact of This Cleaning Technique
While it sounds like a great idea, most modern grills simply cannot handle the heat from this approach. When most gas grills were made with heavy cast-iron parts, this wasn't a problem. Today it is. A modern grill firebox is often made of stamped steel and burners are intended to be consumable parts that wear out and can be replaced.
The intense heat created by this cleaning process can warp cooking grates, crack ceramic igniters, and cause metal fatigue in the burners. Worse, the captured gasses can combust, gas lines and hoses can melt, and the temperature inside enclosed carts can exceed the safe temperatures for storage of propane tanks.
Grill Manufacturers Weigh In
The major grill manufacturers have issued statements that warn consumers to avoid the aluminum foil cleaning practice due to safety concerns. The official position of Weber is:
Weber does not recommend this type of method at all. Covering the cooking surface could trap gas and become a fire hazard and blocking the airflow causes very high heat that can damage valves, burners and supply lines that may make the grill unsafe to use. We do recommend consumers always preheat their grill on high for 10-15 minutes. This will burn off all of the food particles and prepare the grill for grilling.
Char-Broil provides this statement:
We agree, it’s simply a bad idea to clean any grill in this manner. It’s also particularly dangerous. Blocking off the grate can overheat the entire firebox, and force heat into areas not necessarily designed for excessive heat. The firebox could warp, the porcelain could overheat and bubble or burn off/drip off, the gas train (valves, manifold, hoses, tank) could overheat causing catastrophic failure, hot flue gases could be forced out through the various holes in the firebox, which could lead to damaged side shelves. Consumers should always follow the manufacturer’s recommended cleaning methods.
Several other manufacturers have similar comments. Unfortunately, some reputable media outlets still point to the foil incineration method (as it is sometimes called) as the best way to clean a dirty gas grill. Since manufacturers warn against it, the gas grill's warranty may be voided if the grill is damaged by this process.
If anyone is advocating this method of cleaning a gas grill, do not follow the advice, even if they claim to have used it successfully. It's possible that a grill may accept this treatment one, twice, or even more often, but eventually, the chances of destroying the grill or causing a serious accident are very high.