Kill a watt, how accurate?

JiminDenver wrote:
Wanting to know just how much power the window shaker uses, I bought a Kill a watt. It's been to cold to test the AC but most things I have tested are under the rated watts.

The 1875w hair dryer was only pulling 1660w. The oil filled heater pulled 590w on the low 600w setting but only 1380w on the 1500w high setting. Is this normal?

having worked as a designer of test equipment and UL etc. what I can say is that when it comes to listed power ratings, UL is very picky. do NOT exceed the listed power under any conditions. Therefore, our listed power was always more than what the typical draw was. As an example the hair dryer watts probably takes into account max line voltage of near 130V, and min resistance of the coil of wire. Same with the heater.

What I've found is that the killawat is accurate enough for my needs, and probably is pretty accurately measuring the actual power draw of the devices in question under your test conditions.