You may have heard a lot about radiant barrier attic foil lately and how “amazing” it can be in saving you money on your energy bills. As a leading manufacturer/supplier of radiant barrier, I am the first to sing the praises of radiant barriers either installed by do-it-yourselfers or professional installers. However, one should always remember the old saying, “If it sounds to good to be true, it probably is”. The key to understanding your potential savings is to understand how radiant barrier works and be realistic in your expectations.
First, what exactly is radiant barrier? Let’s take a trip back to 7th grade science class and remember that heat flows three ways: 1) Conduction 2) Radiation 3) Convection. The main two forms of heat flow into a home are by conduction and radiation.
Conduction is heat flow through physical contact. If you put your hand on a hot skillet you will experience conduction in its purest form. Heat will instantly move from the skillet into your hand. Heat ALWAYS moves from hot to cold. In your home, conductive heat flows through your walls. (Hot outside, cool inside – Heat is coming in.)
Radiation is heat in a wave-type form (similar to sound waves) that travels across either an air space or a vacuum. You FEEL radiant heat without actually touching the heat source. Using the hot skillet example again, if you put your hand above the skillet you will FEEL the heat from the skillet without actually touching it. Radiant heat will also roast marshmallows on a freezing night or make your face FEEL warm on a cold-sunny day.
Radiant heat travels at the speed of light until one of two things happens: The heat (energy) is either ABSORBED or REFLECTED. Everything absorbs SOME radiant heat. A dark roof absorbs almost all this radiant energy and can easily reach 170º on hot, sunny days. This heat is then re-radiated in all directions. This heat has to go somewhere, and the next thing in line is your attic insulation on your ceiling. It too will eventually heat up. This is like throwing a hot blanket over your home.
Without a radiant barrier, the top surface temperature (not air temperature) of your attic insulation can reach >130º. When this happens, your ceiling THINKS and ACTS like it’s >130º outside. No wonder, you can’t stay comfortable and your AC unit runs all the time. This is a HUGE difference between inside/outside temperatures. As a result your home uses a lot of energy (money) to pull the heat out (air conditioning) and keep you comfortable.
Wouldn’t it be great to KEEP the heat out in the first place rather than paying to get it out AFTER it gets in?
Radiant barrier attic foil BREAKS this path and keeps the radiant heat out. Rather than absorbing the heat like most products, radiant barrier REFLECTS a full 97% of the radiant energy. Essentially bouncing the radiant energy back to where it came from. Don’t worry about increased roof temps. Studies have shown that roof temps only go up between 2-10º on roofs with radiant barrier.
After installing a radiant barrier, the top surface temperature of the insulation will usually be within a few degrees of ambient (outside) air temperature. Everybody always talks about a “Cooler Attic” which is nice, but really what we want is the TOP of the insulation to be cooler. Reducing the difference between the inside/outside surface temperatures is the key to energy savings and comfort.
Some companies make wild claims of 30-50% savings by installing radiant barrier foil insulation. Don’t believe every claim you hear. “Normal” savings are usually in the 10-25% range with some cases up to 30% or more. Radiant barrier attic foil can ONLY reject heat coming through the roof/ceiling. Therefore, a one-story home will reject more heat than a two-story home since it has proportionally more roof surface area. Be realistic in your expectations, the larger roof you have the bigger percentage impact radiant barrier will have. Of course, radiant barrier will help any home to reject heat gain.
Think of foil as shade for your home. If the heat never gets in, you don’t have to pay to get it out. It’s that simple.
I've written several other posts on this that you might be interested in. Check these posts below: