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Convection Heating vs. Radiant Heating

Hands-Warming-Over-Heater

Space heaters are the most effective way to heat small, enclosed areas. The two most common heater types are convection heaters and radiant heaters. Each one offers different advantages and each operates on different principles. Convection heat warm the air. Radiant heaters warm your body. Their effectiveness depends greatly on the conditions and environment they're used in. To understand where and how to use them most effectively, you need to understand how each works and why.

How Convection Heaters Work

There are three methods of heat transfer. The most basic is conductive heating, which is what occurs when two objects of different temperatures are brought into direct, physical contact with one another. The warmer object transfers heat into the colder object, raising its temperature until both objects are in thermal equilibrium. The second method is conductive heating. It occurs whenever a warm object is introduced into a fluid medium like air or water. The particles in direct contact with the heat source absorb heat from the object (conductive heat transfer), which causes them to expand and rise, displacing the colder, denser particles above them and forcing them to move in and fill the space they left behind. As these particles come into contact with the heat source, they warm up and expand as well, creating a cycle of displacement and warming known as a convection current. The current moves particles around the room, bringing all of them into contact with the heat source until the room has reached a uniform temperature. The larger the space, the longer this takes. Because air particles have to be drawn in by the convection current to be heated, air is a poor heat conductor. Any exchange with the outside, such as drafts or thin walls (which absorb heat from the air), makes it even less effective, which is why convection space heaters work best in small, enclosed spaces.

Types of Convection Heaters

Not all convection heaters generate heat using the same mechanism and not all are built for the same purpose. Some are built for personal use, while others are powerful enough heat your whole house.

HeaterHeating Mechanism
Oil Filled HeatersGenerates heat with an electric resistor connected to heating fins filled with diathermic oil. When electricity is applied to the resistor, heat is absorbed by the fins and radiated into the surrounding air
Ceramic HeatersGenerates heat by running electricity through metal coils attached to ceramic plates. The plates absorb the heat from the coils and radiate it out. More compact than oil-filled heaters
Water Space HeatersGenerates heat by boiling water with an electric heating element and converting it into steam. The heater keeps the steam contained instead of letting it boil off, so the heat is absorbed by the air in the room. Similar to oil-filled heaters, but faster. Water conducts heat better than oil
Furnace HeatersGenerates heat by burning gas and oil. Normally kept in basements and used in central heating systems. The heat is distributed  through air ducts in the walls and floor
  
Some convection heaters use a fan to enhance the heating process. The fan forces air over the heating element and blows it out into the room. This not only speeds the distribution of heat, but pulls cool air into the unit faster, accelerating the convection currents operating within the room. The only downside is the noise, which can be quite considerable in a small space.

How Radiant Heaters Work

Radiant heaters operate using the third method of heat transfer, radiation. All objects radiate heat in proportion to their temperature. Radiant heaters exploit this principle by running electricity through a heating coil and converting it into infrared heat that radiates into the surrounding space. Radiant heat waves don't affect the air. In fact, none of their energy is lost to the medium they travel through. It's the reason the sun's rays feel warm when they reach us. The radiant heat from the sun doesn't get absorbed by the space in between. Infrared heat is absorbed by your body and the objects around it. Not only does it raise their temperature, but once they've absorbed enough radiation, the objects around you begin radiating heat and raising the temperature of the room as well. Infrared heat waves spread out and become more diffuse as they move away from their source, which is why most radiant heaters use reflective paneling or fans to concentrate their heat in one area. It makes them more efficient, but it also means they can't heat anything outside their field of view and you have to be close to them to feel their full effects.

Types of Radiant Heaters

There are several different types of radiant heaters. Some are small and compact, while others need to be built into the floors and infrastructure of your home.

HeaterHeating Mechanism
Electric HeatersGenerates heat by running electricity through metal coils. Commonly used in space heaters, but can be found in larger, industrial and agricultural heaters as well
Gas HeatersGenerates heat by burning propane or natural gas to warm heating coils. Requires ventilation to dispose of hazardous waste fumes created by burning
Floor HeatersGenerates heat by warming electric coils or tubing filled with water and air beneath concrete, plywood, or ceramic tiles in your floor. The heat is absorbed by the tiles and radiated up into the room. Air tubes are normally heated with solar energy while water tubes are heated by water pumped from the broiler
Radiant PanelingGenerates heat by heating electric coils or water tubing connected to aluminum panels on the floor or ceiling. The panels absorb the heat and radiate it out into the room
  
Radiant paneling and floor heaters are a popular way to heat bathrooms. Radiant heat isn't affected by steam vents the way convection heaters are, so none of their heat is lost to the surrounding environment.

Which Heats Faster?

AH-470-Fireplace

NewAir AH-470 Flat Panel Space Heater

The effectiveness of radiant and convection heaters depends on the area and persons you're trying to heat. Rooms with bad insulation, drafts, and high ceilings are ill-suited for convection heaters. Warm air rises as it expands, it accumulates along the top of high ceilings, away from the living space, increasing the amount of time and power required to heat the room. Cracks or other openings exposed to outside air either draw out warm air or allow cool air to seep in, upsetting convection currents and the heating process. Uninsulated walls absorb heat from air particles as they come in contact, which reverses the convection process by removing heat from the room.

Radiant heaters aren't affected by these conditions. The electromagnetic waves they produce provide immediate comfort and warmth to all persons in their field of view. It's the reason why infrared heaters like the NewAir G56 Electric Garage Heater are used in garages, warehouses, or jobsites. They can also be used outdoors in patios, restaurants, and construction sites. Radiant heat also takes longer to dissipate once it's been absorbed, so rooms stay warmer longer when radiant heat is used.

Where radiant heaters struggle are in spaces where you want to move about freely or spaces where it's necessary to warm several people spread out over large area. Because their heat is directional and dispersive, they're incapable of heating objects over a wide area or far away. Like a campfire, you have to remain physically close to them to feel their heat. They only way to compensate is to mount them on the ceiling or walls, to increase the effected area, or by increasing their power levels, which also raises fire risk. Convection heaters don't have these problems. Convection currents distribute heat evenly throughout the entire space, which is why they're often the best choice for homes, dorm rooms, bedrooms, and offices.

Final Thoughts

When used correctly, in the proper environment, convection heaters and radiant heaters provide homeowners with comprehensive heating solutions for every room in their house. They heat small spaces at a fraction of the cost of your central heating system, and can even be combined into the same unit like the NewAir AH-470 Flat Panel Space Heater, which uses multiple heating techniques to warm you faster than either could on their own.

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