Welcome to the Energy Efficiency Myths series from Direct Energy! As many myths arise from incomplete knowledge, they can create seemingly possible answers that many people accept as fact. Each month, we will examine common misunderstandings about energy efficiency — whether it’s in your home or about the energy industry — and deliver real facts behind the myth (and how they they might be costing you money).
Radiant Energy Barriers Just Aren’t For Northern Homes
Among home energy professionals, there’s nothing so controversial as to whether radiant energy barriers make economic sense for use in northern homes or not. While manufacturers and sales people tout its effectiveness for cooling homes in Texas and Florida, they make a lot of head-scratching claims when it comes to keeping northern homes warmer in the winter for less money.
Basically, there are three ways that heat energy is transferred. First is conduction, where heat moves from one material into a colder material by physical contact. For example, insulation works like blanket to slow down conduction. In convection, fluids or gasses rise above the surrounding cooler liquid or gas.
Radiant heat is actually electromagnetic radiation, but we know it easiest when an object is so hot that it radiates or “shines” heat outward —such as a red hot piece of metal. If you put your hand up near the underside of your attic’s roof decking on a sunny day, you’ll feel heat radiating from it.
The idea behind radiant energy barriers is to reflect the radiant back towards the source. Consequently, you want something shiny and reflective but that also doesn’t absorb and then emit a lot of heat. Radiant energy barrier is a type of foil and some brands are foil and bubble-wrap material. For it to work to reduce heat gain, there must be an air gap between it and the source of the radiating heat. The minimum gap is usually about one inch. If there is no gap, then the barrier will conduct heat.
Since the summer sun in southern states is closer to a 90° angle, roofs in Texas and Miami absorb a LOT of heat from the sun. All that heat energy radiates into the attic. Unfortunately, southern homes generally have HVAC handlers and ductwork located in the attic. All that radiating heating also heats up the ductwork and HVAC system, increasing the home’s cooling load. Ideally, a radiant energy barrier shields the attic contents from the radiating heat energy.
But the further north you go, the lower the impact of radiant heat makes on a home. There might be the odd heat wave but on the whole, normal summer temperatures in Wilkes-Barre, PA, tend to be cooler than Houston, TX. Further north, the sun strikes the roof at more of an angle, ductwork and air handling are located in the basement, and because of longer winters, there tends to be much more insulation in the attic.
The Salesman Said Savings
Sure, it’s true radiant barriers will save money IF you live in the deep south. Beyond that, it really depends chiefly on how much insulation is in your attic. Oak Ridge National Lab (ORNL) tests showed that for attics insulated to R-19 (6 inches), a radiant barrier could reduce the summer cooling bill by 2% to 10%. If you have little or no insulation, a radiant energy barrier can reduce the amount of heat moving into the living space below by 40%. But if you have R-30 or better insulation, then the amount of savings you might expect from installing a radiant barrier actually shrinks.
In northern climates, the focus is mostly on winter heating, making insulation key. For states from Virginia northwards, the recommended attic insulation amount is R-38 to R-60. All the same, there are lots of smiling pitchmen out trying to make a sale.
According to several manufacturers, placing a radiant barrier on the attic floor over insulation provides substantial energy savings. Indeed, one even says, “In climates where the majority of annual energy usage goes towards heating the structure, a radiant barrier on the floor of the attic above the insulation and ductwork will provide substantial energy savings.”
For radiant barriers to work, they must have that air gap to reflect the radiant heat back downwards. Part of the installation cost would have to include a suitable support framework, which would add to that cost. If it’s not done, then the radiant barrier can only offer a puny insulation R-value of 1.
There is the possibility that installing a radiant barrier over your insulation might cause problems with condensation and mold growth. In spite of the promise of air sealing and recommended use of perforations by radiant manufacturers, Energy.gov warns that radiant barriers “…will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.”
Even then, the reduction in heat flow (not cost) when R-19 attic floor insulation is covered by a radiant barrier is only between 1% and 19%. You might save a little money if you have less than R-19 but the cost of adding more insulation into your attic may be turn out to be cheaper and more effective than a radiant barrier.
With all this in mind, if you live in a northern state and are considering installing a radiant energy barrier, do your family a favor. Tune out the salesman’s hype. Get a better handle on the factors affecting your home, compare the costs of a radiant barrier versus adding in more insulation. Plus if summer comfort is a concern, consider cheaper alternatives such as landscaping for shade to help cool the area around your whole home and increase your home’s curb appeal.