Wall furnaces (AKA gas wall heaters) and electric wall mount heaters provide a lot of heat quickly to medium and large sized rooms. Wall furnaces are a type of vented gas heater that typically comes in two formats: a low profile that is tall and slim, and a squat profile that fits under raised windows. Both types of gas wall furnaces are not connected to central heating, vent to the outside and do not typically require ductwork. Empire and Dayton are among the top brands. Products differ by gas type, BTUH input/output and dimensions.