What Is Radiant Heat?
Radiant heat is heat that travels in a straight line from the source of the heat -- campfire, stove, electric heater or radiator -- to the person or thing being heated. Standing around a campfire on a cold day is an excellent example of radiant heat; the air may be icy cold, but heat travels from the fire to you, warming you. When placed in an enclosed space, the heater will eventually warm the air of the room as it comes into contact with the heater; air in other rooms will remain cold, since walls block most radiant heat.
What Is Convection Heat?
Convection heat uses the motion of hot air to heat a space. By placing a heat-reflecting shell around the source of heat, usually a flame or electric element, a convection stove or furnace focuses all its radiant energy on the air inside it. This air is superheated and rises, either to the top of a room or through the duct systems of a home. As the air cools, it sinks and is drawn back into the heater to be reheated and circulated again.
Examples of Radiant and Convection Systems
Forced-air heating systems (recognizable by ductwork and vents cut into the floors of rooms) are convection systems that use the force of the hot air generated in the furnace to pump the air around the house. It is also possible to buy convection wood stoves and furnaces that heat a single room, but do so by venting hot air upwards.
Radiant systems are common in older houses, where large steam or hot-water radiators sit against the walls of each room. Baseboard strip heating is also a radiant system, as are older wood stoves.
Where to Use Each Type
Broadly speaking, radiant systems are better if you have high ceilings in the room, since the radiant heater doesn't shoot hot air upwards above people's heads, or if the occupants of the room prefer a direct heat.
A single radiant heater isn't much use at heating multiple rooms. For that you'll need a radiant heater in each room or a forced-air system that uses convection to bring heat from one furnace to all the rooms through the ductwork.Convection systems heat rooms more evenly and have fewer surfaces on the heater that are hot to the touch. Since they send hot air upward, they are more effective in lower-ceilinged spaces.