Instruct: Classify Amazon reviews into positive or negative sentiment
Query: A lot of heat for a little power

At the low setting of only 400 watts, this heater produces a lot of heat! I am in the bottom unit of a very old building (built around 1900), so it is freeeezing! This heater has really helped! I keep it under my desk at my home office and it keeps me working. Before, I purchased a couple of energy-efficient 400 watt wall-mounted heaters (for over $80 each), but those take far too long to heat up (by the time the room is warm, I'm ready to leave). This affordable ($30) Optimus heater gives you instant gratification and plenty of heat. I haven't even used it at the 800 watt setting yet. I think I might buy another one or two for the other rooms of my house.