A radiant barrier is a highly reflective, low emissivity foil, used as a type of insulation system to permanently reduce energy costs. Radiant barriers are ‘technically’ not an insulation material, due to the fact they are only a thin sheet of reinforced aluminum foil, however with an air space of approximately 3/4″ or more, radiant barriers have a theoretical R-value of 53. Radiant barriers affect radiant (radiation or Electromagnetic) heat transfer, the single most efficient type of heat transfer, by reflecting that radiation away from the radiant barrier. A typical home will loose heat in the winter and gain heat in the summer and the majority of that heat is radiant heat, so stopping radiant heat transfer in both the winter and summer months is the most effective way to reduce energy cost.
While results will vary from climate to climate, attic installed radiant barrier will reduce heat gain through the ceiling by roughly 40%, which translates into a 17% average reduction in heating & cooling costs. The local climate and the installation technique chosen, will affect the performance of the radiant barrier, so be sure to choose the right installation for your local climate.
While this 17% figure holds true for many climates using a typical installation, it will vary from place to place. Many independent studies and radiant barrier users have tested their results and reported energy savings varying from as low as 12% up to as high as 39%.
Below is one such independent study in which the attic temperature of two similar neighboring houses where tracked over the course of one day. As you can see from the image below, the attic with radiant barrier(blue) performed quite nicely and stayed very close to the ambient temperatures outside(green) when compared to the house with no radiant barrier(red).
Factors Determining Radiant Barrier Effectiveness:
- Attic Ductwork – If ductwork or air handlers are located in the attic, the temperature of the attic area will affect the efficiency of the HVAC system. Using a radiant barrier to control attic temperatures will increase the HVAC system’s efficiency, thus reducing energy costs.
- Existing Insulation – If existing attic insulation is less than a R39, a radiant barrier installation will help to stop excess radiant heat. Homes with a R39 or higher ceiling-insulation, and have no ductwork in the attic will not achieve much energy savings from a radiant barrier installation.
- Cold Climates – In climates where the majority of annual energy usage goes towards heating the structure, a radiant barrier on the floor of the attic, above the insulation and ductwork will provide substantial energy savings.
- Hot Climates – In climates where the majority of annual energy usage goes towards cooling the structure, a radiant barrier stapled to the bottom of the roof rafters will provide maximum energy savings.
- Mild Climates – In more mild climates where neither heating nor cooling is used much, a radiant barrier installation will not create massive energy savings. However, the radiant barrier will increase the overall comfort of the structure while providing small to moderate energy savings.
In order to understand how and why radiant barriers are so effective at reducing heat transfer, you must first understand how heat transfer actually works.
How Heat Transfer Works:
There are three basic types of heat transfer from least efficient to most efficient; conduction, convection and radiant. I am going to use a kitchen analogy to help explain the different types of heat and the different methods of controlling them.
Conduction is the least efficient method of transferring heat and in our kitchen analogy, that would be an equivalent of boiling water in a pot over a stove. The fire heats the pot and the pot transfers its heat to the water and the water eventually comes to a boil. The key point here is that conduction is the transferred through direct physical contact.
Convection is more efficient than conduction, and in our kitchen analogy would be the use of an oven to heat some food. Convection heat transfer is the process by which heat is circulated in an area through the air and/or fluid. The key point here is that heat is transferred through air/fluid circulation.
Radiant heat otherwise known as thermal radiation is the most efficient type of heat transfer and the best example in our kitchen analogy would be the use of a microwave. Radiant heat is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. In a home or building, radiant heat refers to heat radiated from materials, incandescent lights and the sun. It is also important to note that radiant heat moves through the air without heating the air, instead it will heat the first surface that it touches, and this surface will then re-radiate that heat in the space making it feel warmer when you are in that space. This principle causes interior spaces to feel hotter in the summer and reverse during winter months where interior heat is radiated towards the outside of the structure.
The following images help to explain the difference between conductive, convective and radiant heat transfer.
How Radiant Barriers Work?
A radiant barrier is a reflective insulation type system that offers a permanent way to reduce energy costs. Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool. These products use their ability to absorb or resist convective and conductive heat transfer to insulate (R-value). Radiant barriers are not an insulation material, due to the fact they are only a thin sheet of reinforced aluminum foil, however with an air space of 3/4” or more, radiant barriers have a theoretical R-value of 53.
Radiant barriers address radiant (Electromagnetic) heat transfer, the single most efficient type of heat transfer, by reflecting that radiation away from the radiant barrier (as shown in the image above). A typical home will lose heat in the winter and gain heat in the summer and the majority of that heat is radiant heat, so stopping radiant heat transfer in both the winter and summer months is the most effective way to reduce energy cost. Ra-flect™ radiant barrier reduces energy costs in both summer months and winter months because it is double sided, and will keep heat in during the winter months and reflect radiant heat away during the hot summer months. Installing a radiant barrier in your attic is the most cost effective way of reducing your heating and cooling cost while providing the quickest payback(less than a year) of any energy efficient material or product.