Once you have settled on the type and style of an electric fireplace that you're interested in, it's natural to consider adequate heating next. If you're using your heater as a supplemental source of heating, a good rule of thumb for knowing how much power you need is multiplying the square footage of your room by 10.
Total Area (sq. ft.) x 10 = Required Power in Watts
Most electric fireplace models operate between 750-1500 Watts of power, which makes them most suitable for rooms up to 150 sq. ft., which covers most living rooms and A/V rooms.