A British Thermal Unit (BTU) is a standard unit of energy used in the United States and sometimes in the U.K. On the most basic level, it’s the amount of thermal energy needed to raise the temperature of one pound of water by one degree, specifically from 39°F to 40°F.
For our purposes, BTU is a measurement of thermal output of a heating or cooling appliance. For example, in the air conditioning industry, BTUs refer to how much heat the air conditioner can remove from the surrounding air. In the grilling industry, BTUs are a measurement of how much heat a grill generates at its maximum output.
If you think of BTUs like your car’s fuel efficiency or MPG (miles per gallon), BTUs measure your grill’s fuel efficiency or OPB (output per burner) as well as all the burners combined. Since the number of BTUs for all burners combined is a bigger, more impressive number, it’s the number that’s usually promoted to sell grills. It may seem like anything with a high BTU rating (grills, fireplaces and heating equipment) will be hotter and therefore better. Though BTU rating does influence temperature, it’s far from the only thing that determines how hot your grill can get.
For instance, airflow is an important factor in reaching and maintaining high temps. Even if a grill has the highest BTU rating, if it doesn’t have good airflow, it won’t necessarily be hotter. In fact, it will very likely have hot and cold spots.