Radiant Barrier – How it works to save you money!

 

From www.atticfoil.com:

The difference between radiant heat transfer and conductive heat transfer is really quite simple. Radiant heat is heat transferred across an air gap/space (or a vacuum), while conductive heat transfer is heat transferring through materials/objects that are in contact (touching) one another.

This is important because many times people would like to use a radiant barrier to stop heat transfer but they do not have an air space in the assembly they are working with. Without an air space, a radiant barrier will NOT work!

Why? Because radiant heat transfer requires an air space for the heat to transfer. When the air gap does not exist, the materials/objects are touching and so the heat is transferring via conductive heat transfer (conduction).

  • Radiant Heat: heat transfer across an air space
  • Conductive Heat: heat transfer between touching obejects
  • In an attic you have BOTH radiant heat and conductive heat.

air gap  radiation thumbnail

no air gap  conduction thumbnail

Surface Temperatures in the Attic

When the goal is having a cooler home, we need to examine the surface temperatures in the attic. Remember, the attic has both surface temperatures and air temperatures.

Bottom line: getting a cooler, more efficient home is all about the surface temperatures.

Surface temps can only be measured with an infrared thermometer, while air temps can be measured with probe thermometers. The surface temperatures in your attic are basically what tell your home whether or not it is hot outside; this directly effects whether or not your air conditioner turns on and runs. When the attic gains radiant heat from outside, it re-radiates that heat through the attic air and the insulation on your attic floor absorbs it. When your insulation is 130 degrees, your house thinks it’s 130 degrees outside because it essentially has a 130 degree blanket on top of it! By stopping the radiant heat gain in the insulation, with a layer of radiant barrier foil, we can reduce the top surface temperature of the insulation and when the insulation is cooler, the home is cooler and the air conditioner is more efficient.

 

Visit www.atticfoil.com for informative DIY videos and installation methods.

 

This entry was posted in Attic Ventilation, How to Save? and tagged , , , . Bookmark the permalink.

2 Responses to Radiant Barrier – How it works to save you money!

  1. John Pazos says:

    Mark, it looks like you have been doing well. I just found your website and I like it. You have lots of good info on it. I would like your opinion on something. I read about radiant barriers and ended up buying and installing the barrier material from Atticfoil. I installed it on the underside of the roof rafters. I found it to be a great product that is very durable. I installed it almost two years ago while we were constructing an addition to our home, so tracking past against current energy consumption isn’t as straightforward as I would have preferred. I found that the attic air temperatures are lower, but not that much lower. I have plenty of ridge vents (maybe 60′) and soffit vents all around the perimeter, so I didn’t originally think that air movement would be a problem. I am now having second thoughts about that and thinking of adding one or two attic vent fans to force more air circulation up and through the attic. What do you think? I live in Slidell, LA, so it is hot and humid most of the year.

    • joulefool says:

      Hi John,

      Great to hear from you. Yes, tracking energy consumption is not straightforward. I am currently looking to put AtticFoil in my attic this Fall. I live in Denver, so I will be laying it on top of the insulation instead of on the back side of the rafters. It could be that you have the AtticFoil installed correctly but have other attic leaks that are negating its effectiveness. According to the US Department of Energy, you fall in climate Zone 2 and should have between R30 to R60 in your attic. I would also check and make sure you don’t have leaks around your attic hatch and that you seal up any vent tube penetrations through the attic. I would also make sure you have the 3-6 inches of gap from the foil to the top of your ridge to allow the hot air to pool and escape.

      In terms of monitoring energy usage, you can install a whole home energy monitor. I used one from Blue Line innovations to track energy usage. Click Here to learn more http://www.bluelineinnovations.com/

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