BTU (British Thermal Unit) is the traditional unit of energy. The heat value of fuels and the heating power of gas grills can be expressed in terms of BTU. It can be defined as the amount of heat energy needed to raise the temperature of one pound of water by one degree Fahrenheit at a constant pressure of 1 atmosphere. This unit of measurement helps us to compare the heat content of different types of fuel.
Whenever you shop for a gas grill and come across its BTU rating, try to find out which BTU the manufacturer mean. You have to find out if it is that of the primary burners or all the burners combined. If the grill do not have a sear zone, then you should pay special attention to the BTU rating of all the main burners (i.e. those burners that are directly under the main cooking grate where you grill). If you add the BTU rating of the primary burners and divide it by the main cooking grate area you'll get the BTU per square inch of main cooking area. For example, if the primary burners of a gas grill have a 35,000 BTU rating and the main cooking grate area is 500 inches, the grill will then have 35,000/500 = 70 BTU per square inch of main cooking area.
How many BTU do you need? The rule was once 100 Btu per square inch of main cooking area. This rule no longer applies because modern gas grills are now becoming more and more efficient at holding heat. One thing you should know is that the temperature a gas grill can attain is not influence by the BTU rating alone. Also in gas grills, BTU rating is not always directly proportional to the temperature the grill can attain. There are several factors that influence the maximum temperature a grill can reach, one of them is the ability of the grill to retain the heat. Grills that are constructed from lightweight materials cannot retain the generated heat and so will require a higher BTU rating for them to reach a higher maximum temperature. Good grills that can reach high maximum temperature are made with heavy materials (heavy cooking grates) and their lid will close tight. Due to improved efficiency, some modern gas grills can reach high temperature with a BTU rating as low as 80 BTU per square inch of main cooking area.
Gas grills with low BTU rating burn less fuel than those with higher BTU rating. Let's illustrate this by calculating how much propane the primary gas burners will consume per hour. Propane has a BTU rating of|We know that propane has a BTU rating of} 15,000 BTUs per pound. Assuming that the primary burners of a gas grill are rated at 30,000 BTU, the formula for calculating the amount of fuel they'll consume per hour can be gotten by dividing the BTU rating of the primary burners by the Btu rating of propane. Doing this will give us 2 pounds per hour. Similarly, a 45,000 BTU primary burners will consume 3 pounds of propane per hour. Therefore, higher BTU rating of a gas grill will translate to higher rate of fuel consumption. But note that this calculation is made with the assumption that all the primary burners are set to their maximum capacity (you turn the control knob all the way up).
In order to achieve the very high temperature that can searing steak, some gas grills come with an additional cooking surface called the sear region. You can quickly sear your food in this region before transfering the food to the main cooking area to finish off the cooking.
Finally, prick up your sense of curiosity whenever you see a grill with a very high BTU per square inch of main cooking area (somewhere above 150). This is usually a sign a poorly constructed grill that cannot retain heat and they will consume a lot of gas.
To get more information on gas and charcoal grills, these two articles on gas grill sale (buying guide) and charcoal grills for sale (types of charcoal grills) will be helpfull.
