What Is Radiant Heat In Simple Words?
What is Radiant Heat?
Radiant heat is a form of heat transfer through electromagnetic waves, or radiation. Unlike conductive and convective heat that rely on material contact or air currents to transfer heat, radiant heat can travel through open spaces. For example, you can feel the warmth of a fire without having any direct contact with the flames. The heat from the fire is radiated outward in all directions. The sun also emits radiant heat that travels through the vacuum of space to reach the Earth.
Other common sources of radiant heat include electric radiators, wall heaters, and floor heating systems. These all work by heating up a surface that then emits infrared radiation to heat surrounding objects and people. Radiant heat is commonly used to heat homes and other buildings because it efficiently warms people and objects directly, rather than having to heat the intervening air.
In summary, radiant heat refers to thermal energy that is emitted as electromagnetic waves and can travel through space to directly warm people and objects. It provides a very effective way of heating indoor spaces.
How Does Radiant Heat Transfer Work?
Radiant heat transfer works by energy being transferred through electromagnetic waves or radiation. Unlike conductive or convective heat transfer, radiant heat does not require matter to transfer energy. The electromagnetic waves that carry radiant energy are able to travel in straight lines away from the heat source until they hit an object and are absorbed.
All objects with a temperature above absolute zero emit thermal radiation. The hotter the object, the more thermal radiation it emits at a higher intensity and frequency. When these electromagnetic waves encounter another object, the waves will either be reflected, transmitted through, or absorbed by the object, transferring their energy directly to the object’s surface.
Radiant heat transfer is most efficient in a vacuum where there is no conductive or convective heat loss. It does not heat the medium it travels through, only directly heating objects in its path. This makes radiant heat ideal for long distance heating applications.
Examples of Radiant Heat
Radiant heat is present in many aspects of everyday life. Here are some common examples where radiant heat occurs:
Sunlight
One of the most familiar examples of radiant heat is the warmth from the sun’s rays. The sun radiates electromagnetic waves that travel through space until they reach Earth. When these rays strike objects, they transfer heat.
Fireplace/Woodstove
The glowing flames and embers in a fireplace or woodstove radiate heat that warms people and objects in a room. The heat reaches you directly before warming the surrounding air.
Oven/Cooktop
The heating elements in your oven and cooktop emit infrared radiation to cook food. You can feel the radiant heat on your skin when you stand near these appliances.
Heated Floors
Radiant floor heating systems use hot water pipes or electric coils underneath the floor to create radiant heat that rises up into the room.
Space Heaters
Portable space heaters produce radiant heat from their heated coils or ceramic plates. This directly warms people and objects around the space heater.
Radiant Heat Transfer Methods
Radiant heat is transferred in three main ways: conduction, convection, and electromagnetic waves.
Conduction
Conduction is the transfer of heat between two solid objects that are in direct contact with each other. For example, a hot pan conducts heat to the solid surface of a stove top. Conduction occurs when atoms or molecules with a lot of heat energy vibrate rapidly and collide with neighboring atoms and molecules, transferring the heat energy.
Convection
Convection is the transfer of heat by the movement of liquids or gases. For example, hot air rises from a radiator, transferring heat through the room via air currents and convection. Convection depends on the circulation and motion of heat transfer fluids like air or water.
Electromagnetic Waves
Radiant energy is transferred by electromagnetic waves that travel directly from the heat source to the material, without heating the air in between. The sun transfers heat to the Earth through electromagnetic waves that propagate through space. Infrared radiation from hot objects and fires also transfers heat through electromagnetic waves.
Properties of Radiant Heat
Radiant heat has some unique properties that distinguish it from other forms of heat transfer like conduction or convection. Here are three key properties of radiant heat:
Travels through space, not matter – Unlike conductive heat, which requires direct contact between materials, radiant heat can travel through empty space. Radiant energy moves by electromagnetic waves from its source to the absorbing surface without heating the space in between. This allows radiant heat to cover long distances.
Travels in straight lines – Radiant heat travels along straight lines from the emitting surface until it hits an object and is absorbed, reflected or passes through. There is no radial spread of radiant energy like other methods of heat transfer.
Can be focused and reflected – Because radiant heat moves in straight lines, it can be focused and directed using reflectors or lenses. Reflective surfaces like mirrors can redirect radiant energy. This allows the efficiency and direction of radiant heat to be controlled.
Advantages of Radiant Heat
There are several key advantages to using radiant heat systems in homes and buildings:
Energy Efficient
Radiant heating is extremely efficient. Unlike forced air systems that heat the air which then loses heat as it circulates, radiant heating warms objects directly. This direct transfer of heat uses less energy.
Uniform Heating
Radiant heating provides consistent, even warmth throughout a space. The heat spreads evenly across floors, walls or ceilings, eliminating cold spots or drafts.
Doesn’t Circulate Dust/Allergens
Radiant heat doesn’t rely on blowing air around a space. This avoids stirring up dust, pollen or other allergens that forced air systems can distribute.
Disadvantages of Radiant Heat
While radiant heat has many benefits, it also comes with some downsides to consider:
Doesn’t heat air – Unlike forced air systems that heat the air in a space, radiant heating directly warms people and objects. This means the ambient air temperature may be cooler. Some find this uncomfortable.
Less responsive temperature control – It takes longer to feel the effects of temperature adjustments with radiant systems. The thermal mass of floors and walls has to heat up or cool down. This lag can make rooms feel drafty at times.
Surface dust accumulation – Radiators and heated flooring can collect dust and allergens on their exposed surfaces over time. This requires more frequent and thorough cleaning.
Radiant Heat Systems
There are several different types of radiant heating systems available on the market today. The three main types are electric, hydronic, and steam radiant heat systems:
Electric Radiant Heat Systems
Electric radiant heat systems use electric wires or cables installed in the floor, wall, or ceiling to produce heat. The electric current running through the wires produces radiant heat that directly warms people and objects in the room. Electric systems are relatively affordable and easy to install but can be more expensive to operate.
Hydronic Radiant Heat Systems
Hydronic radiant heating uses hot water or a water-glycol mixture circulating through tubing installed in the floor, walls, or ceiling. A boiler or water heater heats the fluid, which releases heat as it passes through the tubing. Hydronic systems provide even and consistent heat, though they require more extensive installation.
Steam Radiant Heat Systems
Steam radiant heating uses a boiler to generate pressurized steam that circulates through pipes installed in the floor, wall cavities, or ceiling. As the steam condenses back into water, it releases its latent heat to warm the surrounding surfaces. Steam systems heat up quickly but require regular maintenance.
In addition to the main types above, there are also different installation configurations for radiant heat:
In-Floor Radiant Heat
In-floor systems have heating elements installed within or beneath the floor. This configuration provides direct warming of the floor surface for comfortable even heat.
Wall-Mounted Radiant Heat
Wall-mounted radiant heat uses heating elements behind walls or attached to wall surfaces. This is an unobtrusive option but can cause uneven heat distribution.
Ceiling Radiant Heat
Ceiling radiant heat systems mount heating elements within a ceiling or suspend them from above. Heat is gently radiated downward over the space. However, heat loss can be greater compared to in-floor systems.
Installing Radiant Heat
Radiant heating systems require careful planning and professional installation for optimal performance. Though DIY installations are possible for experienced homeowners, radiant heat involves dealing with electrical wiring, water lines, and potentially underfloor demolition. Leaking tubes or subpar insulation can lead to energy waste and comfort issues.
Hiring a licensed professional installer is highly recommended. They have the expertise to assess your home’s layout and heat loss, design an appropriately sized system, and integrate the radiant installation with other systems. This helps avoid problems down the road.
Some key factors installers consider include:
- Insulation levels – Having proper insulation under radiant flooring boosts efficiency. Additional insulation may be recommended.
- Flooring materials – The floor covering over radiant tubes impacts heat transfer. Stone, tile and concrete work best.
- Boiler integration – Hydronic radiant systems require connection to a high efficiency boiler or water heater.
- Zone setup – Multiple zones allow different levels of heating in different areas of the home.
Radiant heat installation costs vary greatly based on the size of the home, type of system, and local labor rates. Expect to pay anywhere from $6-12 per square foot for electric systems, and $10-20 per square foot for hydronic installations. Getting 3-5 estimates is recommended to find the best value installer.
Maintaining Radiant Heat Systems
For radiant heat systems to work efficiently, they require periodic maintenance. One key maintenance task is bleeding air from hydronic systems. Over time, air can enter the system and create bubbles, reducing the efficiency of radiant heat transfer. To remove air, locate bleeder valves throughout the hydronic piping and open them to release trapped air. This ensures fluid can circulate properly to transport heat.
Another maintenance need for radiant systems is cleaning dust buildup on surfaces. Dust building up on radiant panels or tubing can form an insulated layer that inhibits heat transfer. Wipe down radiant panels and tubing periodically to remove dust. Also vacuum any radiant flooring surfaces regularly.
It’s also important to check radiant heat controls and pumps. Make sure thermostats and sensors are properly calibrated. Confirm pumps are operating and circulating fluid at the right pressure and flow rate. Replace any worn pump parts as needed. Having properly functioning controls and pumps ensures the radiant system runs efficiently.
