Why is one 1875 watt hair dryer less powerful than another 1875 watt hair dryer?

Answer 1

Dryers have power ratings given to them by approval agencies such as Underwriter's Laboratory. This rating is primarily given so that a user can match the power requirement of an appliance with the power rating of the electrical service to which it is connected. For example, a 20 amp circuit breaker is capable of supplying about 2,400 watts of continuous power without tripping a breaker. The intent is that if you have a 20 amp circuit, you can look at the approval agency power rating of all of the appliances you wish to connect to that circuit and, if they total less than rating of the circuit breaker, they won't trip the breaker.

The only power requirement limitation a hair dryer manufacturer must adhere to is that the actual electrical power used by the dryer is less than the rated power. The actual power usage of a number of dryers that we tested, all of which have been rated by UL as 1,875 wats used between 900 and 1,300 watts.

Another factor is how fast the hair dryer blows air. The more mass of air blown across the coils of the heater in a hair dryer per unit time for the same amount of electrical power applied to said heater coils, the cooler the air coming out of the nozzle. In other words, the longer the air is in contact with the heater coils the hotter it gets. If it passes over the heater coils very quickly, it doesn't have time to get as hot.