[Wissa]

Radiant quartz electric heaters are also pretty efficient for small to medium size rooms. On low, most use only about 750 watts and cycle on and off depending upon the thermostat setting.

Excluding something along the lines of a heatpump, ALL electric appliances put out 3,412.14 BTUs per kilowatt hour consumed, and they're ALL 100% efficient at producing that many BTUs per KWH. It doesn't matter if you're consuming the electricity in a $15 portable heater, or a $150 heater, or a TV or stereo, or your refrigerator, or an electric blanket.

I use the $15 heaters for much of my heating needs, although I'm gradually ramping up the heat that I get from passive solar and through capturing heat in thermal storage.

[Errant]

Radiant (Infrared) heaters regardless of what kind (electric, gas, catalytic) rely more on infrared light to heat objects than in heating the air. Below is a link that provides a better description. What you get is more efficient heating from less energy.

http://www.air-n-water.com/infrared-heaters-pros-cons.htm