Instruction: Parse the product information to locate the target attribute, and then provide the extracted value of the target attribute and its source in the output, specifying None if the attribute is not present.

Input:
Product title: Holmes HFH2992-U Whisper Quiet Heater Fan with Digital Thermostat
Product description: This whisper quiet heater is compact and powerful. With it's digital thermostat, you can easily set your desired comfort level. Set the timer in 1 hour increments up to 16 hours to either preheat a room or to automatically turn the heater off.
Product feature: From Holmes, this compact heater fan provides powerful heat, Easy to read and adjust digital controls with LCD display will help you maintain your desired comfort level, Programmable 16 hour timer allows you to control when you would like to turn the heater on or off, Aerodynamic swirl grill for enhanced heat dispersion, The heater shuts off automatically if it overheats
Product brand: Holmes
Target attributes: Heat Source
Answer: attribute: heat source
value: None
source: None