Most Economical Room Heater

economical
Giving good value or service in relation to the amount of money, time, or effort spent
economic: using the minimum of time or resources necessary for effectiveness; "an economic use of home heating oil"; "a modern economical heating system"; "an economical use of her time"
avoiding waste; "an economical meal"; "an economical shopper"; "a frugal farmer"; "a frugal lunch"; "a sparing father and a spending son"; "sparing in their use of heat and light"; "stinting in bestowing gifts"; "thrifty because they remember the great Depression"; "`scotch' is used only informally"
Using no more of something than is necessary
Careful with money so as not to spend too much; prudent; thrifty; Relating to economy in any other sense
(of a person or lifestyle) Careful not to waste money or resources

heater
A person or thing that heats, in particular a device for warming the air or water
A heater is object that emits heat or causes another body to achieve a higher temperature. In a household or domestic setting, heaters are usually appliances whose purpose is to generate heating (i.e. warmth). Heaters exists for all states of matter, including solids, liquids and gases.
A conductor used for indirect heating of the cathode of a thermionic tube
fastball: (baseball) a pitch thrown with maximum velocity; "he swung late on the fastball"; "he showed batters nothing but smoke"
A fastball
device that heats water or supplies warmth to a room

room
Opportunity or scope for something to happen or be done, esp. without causing trouble or damage
space for movement; "room to pass"; "make way for"; "hardly enough elbow room to turn around"
an area within a building enclosed by walls and floor and ceiling; "the rooms were very small but they had a nice view"
Space that can be occupied or where something can be done, esp. viewed in terms of whether there is enough
A part or division of a building enclosed by walls, floor, and ceiling
board: live and take one's meals at or in; "she rooms in an old boarding house"