QMark GFR2004F Surface or Recessed Wall Mounted Register Style Electric Residential Wall Heater The element is a commercial-grade, steel-fin design for long life. A line-voltage wall thermostat or the built-in thermostat accessories can be used to control the heater. The unit has two over-temperature protectors and a patented Clip-n-Fit board that allows for the installer to choose from several wattage outputs. The unit can be recessed in a standard 2' x 4" wall.