Radiant barrier foil insulation is a reflective insulation system that offers a permanent way to reduce energy costs. Radiant barrier foil insulation systems block radiant heat energy instead of absorbing it like fiberglass insulation. Radiant barrier reflective foil insulation is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be. A radiant barrier foil insulation system is a layer of foil facing an airspace and is installed in the envelope of a building.
The 3 Ways to Transfer Heat
Heat is transferred from hot to cold via three methods of transfer: conduction, convection, and radiation.
Conductive: The transfer of heat flowing through a substance (molecular motion) or to another substance that is touching. If you touch something hot, like a stove, your are feeling a conductive heat transfer.
Convective: The transfer of heat in fluids, such as rising heated air, steam, and moisture. If you go outside are hit by a bone chilling wind, you are feeling the effects of convective heat transfer.
Radiant: The transfer of heat via infrared radiation rays that are invisible to the naked eye and unaffected by air currents. When you step outside and feel the sun on your skin, you are in fact feeling the sun’s radiant heat. All materials radiate radiant heat in ranges from 0% to 100%.
Common examples of radiant heat transfer:
· Your skin turn rosy pink and eventually painful after a day in the sun.
· Roof shingles heated via the radiant heat from the sun.
· Heat radiating from a light bulb.
Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool. These products absorb or slow down convective and conductive heat transfers to insulate. These types of insulation do not BLOCK heat - they can only slow it down. Therefore, after a period of time, 100% of the heat absorbed would eventually transfer through the insulation. The rate in which this heat eventually transfers through an insulation material is the material's R-Value.
· Fiberglass and blown-in cellulose insulation rely on air spaces within the material to decrease the conductivity of heat. They also reduce convective heat flows by trapping heating air flows and thereby restricting air circulation.
· Foam insulations work similarly to fiberglass and blown-in insulation. Some foam insulations use hydrochlorofluorocarbons (HCF) to absorb and slow down the transfer of heat via conductive and convective measures. However, the United States has scheduled phasing out the manufacturing and importing of all HCFs over the next 23 years. HCF's, such as those contained in some foam insulation products, are considered very potent greenhouse gases.
How Radiant Barriers Work
A radiant barrier reflects or blocks radiant heat energy instead of trying to absorb it. A radiant barrier can also reduce convective heat transfer by acting as a physical blockade against convective air flow.
How does a radiant barrier reflect/BLOCK radiant heat?
The reflective surface of radiant barriers has two properties that enable it to reflect or block radiant heat when at least one air space is provided on one side:
A Radiant barrier reflects radiant heat that strikes its surface across an air space from a heat source and conversely, it emits very little radiant heat from its surface across an air space opposite a heat source.
Radiant Barrier Articles and Studies:
Appalacian State study on radiant barrier effects of a home with R-30 insulation
TVA Radiant Barrier Study