The Spring & Fall Effect – Can Radiant Barrier Work Against You?

It happens every year. I get a few calls from customers who say “I installed AtticFoil® – it’s a great product and I could really tell a difference in the summer, but now I am having trouble getting my house to cool off at night.  Is the radiant barrier working right?

Ironically the radiant barrier IS working.  It fact, it continues to work sometimes even when you DON’T want it to work.

Remember heat ALWAYS flows from hot to cold.  So, if it is hotter outside than inside your home, heat is flowing IN – typical summer weather.  Or, if it is cold outside and warm inside heat is flowing OUT – typical winter weather.  The problem is that there is typically a period in the spring and fall when the heat flow FLIPS in the middle of the day.  Example:  It may be warm – 80º in the afternoon and heat is flowing IN, then it cools off at night down to 50º heat is now flowing OUT of the house.

The challenge is that radiant barrier does not know that you want your home to cool off on nights like this.  It is just doing its job.  Radiant Barrier will ALWAYS reduce heat flow from hot to cold – even if you don’t want it too.  In the afternoon, AtticFoil® radiant barrier is reflecting heat OUT of the home to keep the home cooler; at night it will help KEEP the heat inside to maintain a warmer home.

Yes, it is true.  There are some days each year when an installed radiant barrier will cause the opposite effect of what you may want, but the solution is usually pretty easy to solve.  In the evening, once the air temperature cools off, you need to flush out the heat your home is holding inside.  The best way to do this is to crack open some windows and run bathroom exhaust fans and/or a kitchen vent hood fan to help pull out the warm air and heat inside the home. I even heard of one customer who would pull down their attic staircase in order to allow air to enter through the windows and escape through the attic.

Fortunately, this uncomfortable period usually only last for a few weeks before the weather changes to consistently hot or cold.  Therefore, the overall benefit of installing a radiant barrier far outweighs this short-term inconvenience.

Interestingly, we have many customers who do not have air conditioning.  They live in mild climates or higher altitudes that cool off significantly at night.  However, even in these areas there are usually a few weeks of the year where they wished they did have air conditioning.  We often hear that installing a radiant barrier has made a huge difference during this period and keeps their home comfortable by not heating up as much – even on the hottest days.

8 thoughts on “The Spring & Fall Effect – Can Radiant Barrier Work Against You?

  1. Green Solutions TPS (Wilmington,NC) claims for $7,400 for approx. 1900 SQ Ft., their radiant barrier will be able to cool my home in summer and heat my home in winter for at least 25% reduction on energy bill. Will this really work? Thanks

    1. Constance,

      Does is sound to good to be true?? Considering the foil cost is between $250 and $350,I think $7,400 is almost criminal. I can probably find you a guy who will fly up and install it for a third that much including the plane ticket. Please read my page on Radiant Barrier – Expected Savings I bet you can find a “handyman” or some college boys to install it for a few hundred dollars.

  2. Ed:

    I am a little confused. I thought that radiant barriers do not have any effect on the air temperature but instead radiates to another surface. If this is the case, how is it possible at night that it would help KEEP the heat inside? If this is true would an attic fan help the situation? Thanks!

    1. Rocky,

      Thanks for the question. The radiant barrier tends to “keep” the heat in more when the Radiant Barrier Over-Insulation Method is used as compared to the Staple Up Method. If the insulation is hotter then the outside and or attic air, the insulation will want to release the heat to the cooler attic/roof both by conduction and radiation. A radiant barrier will reduce the ability of the heat to be released. This is good in the Winter but can work against you in the Spring/Fall on cool nights when you WANT the home to cool off. Good ventilation will help to get the heat out of the attic, but I usually never recommend using an electric attic fan to do this.

  3. Ed,

    I live in a 2-story house with a central forced air heating/cooling system. I have one unit in the attic that serves the second floor, if I install a radiant barrier in my attic it will help maintain the heat in during the winter months, however, during the summer months the HVAC unit will be extracting heat from the second floor into the attic and the radiant barrier will probably maintain that heat inside the attic. Is it recommended to install a radiant barrier in attics that house an HVAC unit?

    Thank you.

    1. Hugh,
      Yes, using radiant barrier in an attic that houses an HVAC unit is not uncommon at all. In fact, it’s pretty much standard here in the south. Make sure you realize the unit is not pulling heat out of the home in the summer, it is pumping in cool air. This is why the vents blow air into the home, otherwise they would suck air out – like a vacuum cleaner. During the summer months the HVAC stands to gain heat that is radiating off the roof (from outside) and it makes the unit use more energy to keep the air it is pumping cool. Eliminating 97% of that radiant heat gain allows the unit to stay cooler easier, and it works more effectively AND efficiently. Check out this page to see photos of HVAC units in attics with radiant barrier:

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