How Radiant Barrier Functions - In Simple Terms

You might have heard a great deal about radiant barrier attic foil of late and how “amazing” it is at saving you money on your energy bills. I’m the first to extol the benefits associated with radiant barriers installed either by professional installers or do-it-yourselfers. Still, one needs to always remember the old adage, “If it sounds too good to be true, it probably is”. The key to realizing your potential savings is seeing how radiant barriers function and adopting a realistic stance in your expectations.

First, what precisely is meant by a radiant barrier? Let us make a trip back to 7th grade science class and recall the three ways in which heat flows, conduction, radiation and convection. The principal two types of heat flow into a home are by radiation and conduction.

Conduction refers to heat flow by means of physical contact. Heat will instantaneously move from the skillet you are holding in your hand. Heat is ALWAYS transferred from hot to cold. Your home has conductive heat flowing through its walls. (Cool inside, hot outside – that’s when heat is coming in.)

Radiation is a type of heat in the form of wave (like sound waves) that can travel across a vacuum or an air space. You can FEEL radiant heat without actually needing to touch the heat source. Using the example of the hot skillet once more, if you place your hand over the skillet, you will FEEL the skillet giving off heat without actually touching the device. Radiant heat is also capable of roasting marshmallows on a frosty night or making your face FEEL warm on a day when it’s cold and sunny.

Radiant heat travels very fast - in fact, at the speed of light - until one of two things takes place: the heat (energy) is either REFLECTED or it’s ABSORBED. Everything absorbs SOME amount of radiant heat. A dark roof can absorb nearly all this radiant energy and can easily attain a temperature of 170 degrees on hot, sunny days. This heat then gets re-radiated in all directions. This heat will end up some place, and the next thing in line is the attic insulation that you have on your ceiling. Eventually, it will heat up also. This is similar to drawing a hot blanket across your home.

In the absence of a radiant barrier, the maximum surface temperature (and not air temperature) of your attic insulation can climb up to more than 130 degrees. When this occurs, your ceiling THINKS and ACTS as if it's over 130 degrees outside. It’s no wonder that it’s not possible for you to stay comfortable and your air conditioning unit runs without a pause. This is a MASSIVE difference between outside/inside temperatures. The result is that your home uses a great deal of energy (read money) to suck the heat out (with the help of air conditioning) and keep you comfortable.

Wouldn't it be just great to PREVENT the heat from coming inside in the first place instead of paying to eject it AFTER it has entered your home?

What radiant barrier attic foil does is BREAK this path and keep the radiant heat from getting in. Instead of absorbing the heat, like a majority of products, radiant barrier REFLECTS a full 97 percent of the radiant energy. Basically, it bounces the radiant energy back to where it came from. There's no need to worry about increased roof temperatures. Studies indicate that roof temperatures only increase between 2 to 10 degrees on roofs equipped with radiant barrier.

After you have installed a radiant barrier, the maximum surface temperature of the insulation will generally be limited to within a few degrees of ambient (that is, outside) air temperature. Most folks appear to always talk about a “Cooler Attic.” That's nice, but what we really want is the TOP of the insulation to stay cooler. By reducing the gap between outside/inside surface temperatures, you will have the key to comfort and energy savings.

Certain companies make fantastic claims of 30-50% savings by installation of radiant barrier foil insulation. Don't get taken in by every claim that comes your way. Most of the time, "normal" savings are typically in the 10-25% range with some instances of savings of 30% or more being noticed. You need to be realistic with your expectations; the bigger the roof, the higher the percentage impact that radiant barrier will have. Certainly, radiant barrier can help any home to get rid of heat gain.

Look at it this way - the foil acts as a shade for your home. If the heat doesn't manage to get in, you don't need to pay to get it out. Turns out, it’s just that simple.