A new series of insulating paints promises energy savings by simply painting. But do they really work?
Typically, insulating paints (also called “nanocoatings” by some vendors) are designed to be applied to a building’s exterior with the goal of reflecting radiant heat energy. These types of radiant barriers have shown to provide benefits when properly applied to roofs, and there are a number of ENERGY STAR-qualified products that can be used for this purpose.
However, radiant coatings for roofs are different from paints that are to be applied to exterior walls. To date, there has not been any definitive research showing that adding such coatings to exterior walls is a cost-effective way to reduce building energy use. Instead, there has been a good deal of material from coating vendors that confuses radiative heat transfer with conductive heat transfer.
For example, numerous coating manufacturers advertise an “equivalent R-value” of their coatings. R-value represents the amount of insulation needed to reduce conductive heat transfer across a surface. One manufacturer claims that test results show that adding its 100-micron-thick coating to a 4-inch concrete and plaster wall decreased the thermal conductivity across that wall by nearly 30 percent. In other words, the manufacturer claims that the coating reduced conductive heat transfer by a significant percentage. Simply considering the scale difference between 4 inches of concrete and 100 microns of paint should illustrate why claims like this should be met with extreme suspicion.