I am a mechanical engineering student and i need to measure electrical output. I have some voltage and current measuring instruments. I used them to measure the voltage & current of a blower(resistance heater). 
The results were 3 ampere and 155 volts. But the appliance is rated at 2kW. So according the formula, P=VI, the load of the appliance should be 155*3=465W. Why does this deficit exist between the rated power and the one i measured. Is there any factor that needs to be introduced in the P=VI formula?. Someone told me its power factor (cosφ) .