How much can radiant barriers save?
Since everyone's home and lifestyle are different, we can't precisely calculate your personal savings from attic radiant barriers. However, it's reasonable to expect that an attic radiant barrier can save 8-12 percent of your annual cooling costs in the Southeast.
Savings from an attic radiant barrier depend on the amount of heat the roof and attic contribute to your home's cooling load. ("Cooling load" is the total amount of heat your air conditioner must remove to maintain comfortable indoor temperatures.) In general, the more energy efficient the rest of your home is, the larger the percentage of energy you save from an attic radiant barrier because the roof and attic make up a larger portion of the cooling load.
Figure 2. Shows a breakdown of cooling loads in a typical 1500-square-foot Central Florida home. The attic (including heat gains to the duct system) accounts for 22 percent of the total cooling load. In this house, an attic radiant barrier could save 8-12 percent on the annual air-conditioning costs.
Although not as significant, heating savings may also accrue from the use of radiant barriers.
Results from a recent comprehensive field monitoring study conducted for Florida Power Corporation (FPC) by FSEC on the performance of attic radiant barrier systems in central Florida homes may be viewed by reading "FPC Residential Monitoring Project: New Technology Development - Radiant Barrier Pilot Project". A good website for help in deciding weather or not to install a radiant barrier system may be viewed at http://www.ornl.gov/sci/roofs+walls/radiant/rb_01 .html.
Are claims of greater savings untrue?
As in most cases, claims for radiant barriers that sound too good to be true are too good to be true. If your roof accounts for less than 20 percent of your cooling load, then an attic radiant barrier can't possibly save more than 20 percent on your bills.
Claims of greater savings may simply be the results of misunderstanding. For instance, FSEC has measured and reported that radiant barriers can reduce heat gain through R-19 insulated ceilings by over 40 percent. If the ceiling portion of the total cooling load is 20 percent, that's a reduction of 40 percent of 20 percent, which amounts to 8 percent savings on the total cooling load.
If all the facts and figures tend to confuse you, just remember that an attic radiant barrier can save about 8-12 percent on your air-conditioning costs in the Southeast. Any Sunbelt homeowner knows that an 8-12 percent saving on air-conditioning bills can be significant.
When will I see a payback from an attic radiant barrier?
Two things affect the performance of a radiant barrier system – the level of insulation in the attic, and the geographic location of the home. A simple answer to the question is that a radiant barrier system reduces the heat flow into the house from the attic by approximately 40 percent. Attic insulation levels have a large effect on the amount of heat flow that is reduced, in other words, if you have little or no insulation in your attic, a 40 percent reduction is very significant, but if your attic is insulated to R-30 or better, there is very little heat flow to reduce. The more of your energy bill that is concerned with heating, the less desirable having a radiant barrier becomes. When you are using your heater, any heat gain from the attic is desirable. There may be a reduction of heat loss through the roof during winter nights, but the climates where testing has been performed do not lend themselves to demonstrating this, as there is very often a brief or non-existent winter. A very helpful website for guidance to the cost effectiveness of installing a radiant barrier is found on Oak Ridge National Laboratory's Web site, http://www.ornl.gov/sci/roofs+walls/radiant/rb_02.html.
In Florida, computer studies conducted in the development of the Florida Model Energy Code indicate that a typical attic radiant barrier installed in a Florida home will offer a six to seven year simple payback and a 15 percent to 19 percent return on investment.
