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reflector in attic

will putting alumnium foil in attic help cut your heating bill if so how much


  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479

    would you be attaching it? I've heard of Folks in Texas putting foil in under the roof to reflect back the infra red waves from the sun to cut cooling costs. I also heard it cut the life of their roof shingles in half as they got a double dose of infra red waves coming and going. Wehre would you install it to help with heating? WW
  • HDE
    HDE Member Posts: 225
    edited November 2010
    Radiant barrier

    It's called radiant barrier and in my new home the silver foil facing was part of the roof sheathing. It significantly reduces attic temp, especially when the roof is in the direct sun. With proper, non mechanical ventilation the attic temp doesn't rise more than 10 degrees outside. This is a huge benefit with cooling season.

    I can't see it assisting heating though
  • Dave Mitlyng
    Dave Mitlyng Member Posts: 6

    in the attic on top of the insulation.The company said it would pay back in 3 years at a cost of 45 cents per square ft.
  • TomS
    TomS Member Posts: 61

    Insulation will generally have a vapor barrier made of foil and this should be facing down to the heated area.  If you were to add additional insulation it should be pure insulation with no foil.  I am afraid by you adding foil on top of the insulation it will actually be worse insulation wise because you will trap moisture.  I have seen many instances where the installer incorrectly placed the foil side up thus allowing trapped moisture from the heated area to collect in the insulation and thus decreasing its R value.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    Somewhere in the Holohan archives...

    Dan had a story about a house that was built way back when, that had nothing but shiny aluminum reflectors built into the walls. As I remember, the theory was that very little radiant energy would be needed to support the house and maintain good comfort conditions. As I remember, it failed miserably, as have many other attempts.

    Bubble Foil Bubble is another fine example of this misapplied theory.

    There is more to heat transfer than just conductive energy transfer, and there is more to maintaining human comfort than just providing heat.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • hot_rod
    hot_rod Member Posts: 20,790
    edited November 2010
    radiant sheathing

    is starting to show up on homes and jobsites around here. Seems it would be a good radiant floor product, shiny side down with transfer plates attached?

    Many of the poultry farms here and in Arkansas use a radiant barrier product suspended under the roof, even in the open side buildings.

    A few years back a manufacturer was sending out sample cans of Radiant Barrier paint. When you wash out the brushes and rollers you end up with a handful of fine aluminum particules.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265

    The first house I built was in 1964. It still has the same paper shingle roof on it. There is no insulation in the rafters. Just between the collar ties.

    I now see houses with 10 to 15 year old roofs failing. Excessive heat.

    If you have AC and you are in Taxas, or anywhere for that matter, put a big fan in the attic and a thermostat to run it. If it is a open attic space, heavily insulate the floor and install fans. Heat flows to cold and dampness flows to dryness. If it is 100 degrees outside and you are trying to maintain 70 degrees inside, that is a 40 degree differential. If your attic space goes to 140 degrees, which isn't all that difficult, you now have a 80 degree differential. A fan, circulating 100 degree outside air will drop the differential back to 100 degrees. It will cost you less to cool your house with 40 degree differential ceilings that 80 degree. You should understand that.

    Aluminum foil is a scam. By someone either well meaning or trying to seperate you from your hard earned cash.

    In New England,, most old houses had roof scuttles. So you could get on the roof and clean the chimneys. And to open in the summer to let air curculate through the house. I call it "Third World Air Conditioning". I have a customer who wanted to put AC in their old house. It was a verfy complicated house to do it in. They got a price of over $60,000 to do just part of the house. They were going to try window air conditioners. I told them to put window box fans in the attic windows and open the windows downstairs. To put a box fan in their bedroom and have the air blowing on their bed. That at night, the air was cooler and that the cooler. dryer air would cause evaporation and that was the basis of cooling. They finally did. For less than $100.00, they cooled their house. With third world AC. In their house in Maryland, they definately need AC. But if you want to cut your cost and not wreck your roof, put in some attic fans. Get a big one. WW. Grainger sells some nice ones.

    I use the same principle on getting rid of excessive dampness in crawl spaces. Blow the cool, damp air out and it will be replaced by warm dry air.
  • icesailor
    icesailor Member Posts: 7,265

    H. Rod,

    There are trade offs in life. What may work in a chicken house may not work so well in a residence. I've not seen a lot of 100 year old chicken houses but I've seen a lot of 100 year old homes with failing roofs.

    A 24'X48' ranch home is 1152 square feet. That comes out to $518.40. You can get a nice fan and thermostat for that.

  • HDE
    HDE Member Posts: 225
    Radiant barrier

    untill you have lived in the south, in an area with 300 predominately sunny days with temps that hit a 100 often, you won't understand what radiant barrier can do for you.

    Perhaps the OP misunderstood where the reflective goes, never in Or on the insulation.

    I can enter my attic on a 90 degree, sunny day and it won't be over 100, with no fans.

    Liked it so much, I added it to a 3.5 car attached garage making the area tolerable in the summer with fans.
  • Solarbord
    Solarbord Member Posts: 1
    Radiant Barriers

    Just a couple of points about this very interesting conversation.  Radiant barriers only raises the shingle temps about 5 degrees (well within shinge mfgrs tollerences).  Radiant barriers can help reduce heating costs but of course that depends on climate etc.  The heat is blocked from leaving the attic in winter the same way it blocks the heat from entering the attic in the summer. 

    A couple of things to keep in mind about radiant barriers that are very important.  An air space is required on the foil side.  If something contacts the foil surface i.e. foam and there is no airspace then the foil simply becomes a conductor and the barrier is lost.  I had a woman from TX call me yesterday wanting to know if spraying foam insulation on the foil would help.  That completely negates the value of a radiant barrier.  The other very important thing to remember is to make sure there is proper attic ventilation and the venting system is no blocked.

    Attic temps with a radiant barrier should be up to about 30 degrees cooler and the FL Solar Energy (a very good web site for info) determined in test houses that a radiant barrier would provide up to about a 17% reduction in the cost of cooling.  Of course that depends on the size, style, location etc of the home and the number of occupents and their life style.

    I hope I have helped.
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