What is a Radiant Barrier? Are they effective at reducing my energy bill?
We inspect a lot of hot dusty attics, some are 165° F. We see all kinds of situations where attic insulation is insufficient, ventilation is inadequate, and rarely find radiant barriers installed in attics. According to the Department of Energy Radiant Barriers work best in hot climates when used in conjunction with sufficient insulation and ventilation. Studies show that radiant barriers can reduce cooling costs 5% to 10%. The reduced heat gain may even allow for a smaller air conditioning system or improve effectiveness of an under rated systems.
Radiant barriers are installed in homes primarily to reduce summer heat gain and reduce cooling costs. Radiant barriers do not reduce heat conduction like thermal insulation materials. The barriers are comprised of a highly reflective substrate or foil that reflects radiant heat rather than absorbing it.
Like a cool spoon in cup of coffee conducts heat through its handle to your hand; heat travels from a warm area to a cool area by a combination of conduction, convection, and radiation. Heat flows by conduction from a hotter location within a material or assembly to a colder location. Heat transfer by convection occurs when a liquid or air, becomes lighter and rises. When liquid or air cools, it becomes heavier and falls. Radiant heat moves from hots surfaces and is absorbed by cooler materials or air. A car parked in the sun will absorb the radiant heat into the cars finish and transfer the heat thru the metal into the interior where it heats the air inside the car.
How Radiant Barriers Function
Most insulation materials work by slowing heat transfer. Radiant barriers and reflective insulation systems are designed to reduce the transfer radiant heat. Radiant barriers must have an air space to work. Radiant barrier are less effective when installed horizontally. Dust accumulation on the reflective surface reduces its reflective properties.
As the sun heats your roof, it makes your roof hot. The heat travels through the roofing materials to the attic side of your roof. It radiates the increased heat energy onto the cooler attic materials, the air conditioning ductwork and the ceiling of your home. A radiant barrier reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic.
Radiant Barriers help air conditioners cooling capacity
Radiant barriers are more effective in hot climates than in cool climates, especially when cooling air ducts are located in the attic. Some studies show that radiant barriers can reduce cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it's usually more cost-effective to install more thermal insulation than to add a radiant barrier.
Frank Carr is the Owner / Inspector at First Choice Home Inspections in Deltona, FL serving Volusia, Seminole, Orange and Lake Counties. Formerly in the building trades, Frank’s focus is a safe home and building FCHI. We believe that consumers have the right to expect the highest standards of thoroughness, fairness and effectiveness from their home inspector and that is exactly what we provide.
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