![]() What is the effect of radiant barriers on heating and cooling bills?Īccording to the Oak Ridge National Laboratory, your savings on heating and cooling bills will vary depending on a number of factors. For example, installing a radiant barrier in an attic that already has high levels of insulation (R-30 or above) would result in much lower energy savings than in an attic insulated at a low level (R-11 or less). The amount of thermal insulation affects the potential radiant barrier energy savings. Therefore, due to the way heat is transferred, you still need insulation. See Section 460.12 of the Federal Register for details. Radiant barriers reduce only radiant heat transfer though, so the rules as applied to determining R-value of the products relate to not only the thickness of the material but how it is installed. The higher the R-value, then the greater the insulating power. The R-value indicates the resistance to heat flow. On the other hand, radiant barriers and reflective insulation systems work by reducing radiant heat gain. Will I still need insulation if I use a radiant barrier?Ĭonventional types of insulation consist of fibers or cells that trap air or contain a gas to primarily retard heat conduction, and, to a lesser extent, convective air flow at various rates. This is why radiant heat transfer can be limited by the use of radiant barriers, which have shiny foil surfaces. Dark, rough surfaces will generally absorb radiant heat and become warm, while smooth, shiny surfaces will reflect the radiation. The earth receives all its solar heat through radiation. Radiant heat transfer occurs when electromagnetic waves travel in a straight line through a vacuum or air between surfaces that are at different temperatures, heating any object in its path. What is radiant heat transfer and why are radiant barriers effective? Although the radiant barrier may be somewhat effective in retaining heat within a cold-climate home, it may also block winter radiant heat gain in the attic. Radiant barriers are most effective in blocking summer radiant heat gain and saving air-conditioning costs. Properties to look for are high reflectivity and very low emittance (the energy radiated from the material’s surface), which enable it to reflect the radiant heat energy and give off (emit) very little. Some radiant barriers have a reflective surface on both sides so either side can face the open air space. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a radiant barrier (sometimes called radiant heat barrier). Reflective insulation placed in walls or on the attic floor must be perforated to allow water vapor to pass through it. Reflective systems are usually located between roof rafters, floor joists, or wall studs. The resistance to heat flow depends on the direction of heat flow with this type of insulation most effective in reducing downward heat flow and requiring an air space next to the reflective side. Reflective insulation systems are usually made from aluminum foils with a variety of backings such as roof sheathing, kraft paper, plastic film, cardboard, etc.
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