Replies

1. 
   NRTRob | Apr 27, 2007 04:30pm | #1

   there is NO SUCH THING as "radiant benefit" under the slab.

   Your mistake is a good one. the concrete may eat the aluminum, but then at least you'll still have foam which is providing a real insulation benefit, not a nearly worthless bubblewrap layer.

   "Radiant" heat transfer is the transfer of heat through space. Objects touching each other do not count. That's conduction, and that requires good old fashioned R-value.

   Smile! You made a better choice than you intended to ;)

   -------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com
2. 
   SamT | Apr 27, 2007 05:09pm | #2

   Radiant foil under slab is worse than worthless. If it wasn't for the bubbles or foam between layers it increase heat flow downward.

   SamT

   Praise the Corporation, for the Corporations' highest concern is the well being of the public.

1. 
   bulwinkle | Apr 27, 2007 05:36pm | #3

   So it sounds like I would be better off removing a couple inches of gravel and putting down foam and a plastic barrier. 

   The literature that I've read gave the fFMf a r-14 I figured that was comparable to 2 inch foam.  Sounds like this a clash of old vs new tech

1. 
   SamT | Apr 27, 2007 05:44pm | #4

   I am a firm believer in radiant barriors. I saw it in use before it was invented. Well before it was commecialized any way. Back in the 50's and it's use spread because of empirical observations. It works.

   Radiant material in contact with conductive material on both sides improves heat transfer. IOW it lowers R.

   Foil faced bubble wrap under slabs is a scam.

    SamT

   Praise the Corporation, for the Corporations' highest concern is the well being of the public.

1. 
   bulwinkle | Apr 27, 2007 05:59pm | #5

   Thanks for the info---P.S. People are not the main concern of corporations; shareholders are! But when the shareholders make money they spend money AND THAT is good for the people. 

1. 
   SamT | Apr 27, 2007 06:11pm | #7

   PS: That's irony below.

   Praise the Corporation, for the Corporations' highest concern is the well being of the public.

2. 
   NRTRob | Apr 28, 2007 12:02am | #10

   I agree with your sentiments samT, but I have to challenge some of your statements here.Aluminum has an R value.. just like everything else. It has some measurable resistance to heat transfer. It just happens to be very low.Adding layers in anything, IF IT DOES NOT CHANGE CONTACT AREA, will not increase heat transfer between two objects that would be in conduction in the first place. There is no such thing as a substances with a negative resistance to heat transfer, as far as I know.Now, it won't slow it down much either. But it wouldn't increase heat transfer to the ground below to have a layer of aluminum, unless the aluminum layer is larger than the slab to ground natural contact area... then, it could conduct more heat from the slab to more area of ground. Or maybe be a radiation fin above ground or something ;)-------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com

1. 
   SamT | Apr 28, 2007 05:47am | #11

   Ok, I shoud have said "it increases heat flow downward over any other material you can put under the slab."

   Even that is not strictly trrue, 'cuz if you used gold, silver,  or diamond,, those would be worse.

                    Thermal     Coefficient of                 Conductivity,                             Thermal Expansion,    Material     Watt/cm .multidot. .degree.C.                             10.sup.-6 /.degree.C.    ______________________________________    Semiconductors    InP          0.80        4.75    GaP          1.1         5.91    GaAs         0.37        6.63    Ge           0.64        5.75    AlAs         --          5.20    InAs         0.29        5.16    Si           1.24        2.5    Metals    Cu           4.0         16.6    Ag           4.3         19    Au           3.2         14.2    Al           2.4         25    Diamond    Type Ia      9.9         0.8.sup.a    Type IIa     23.2        0.8.sup.a    Type IIb     13.6        0.8.sup.a    ______________________________________     Note: .sup.a This value is reported for diamond at 20.degree.

   Worst of all: helium II  (< 2.2 K)~100,000

   SamT

   Praise the Corporation, for the Corporations' highest concern is the well being of the public.

   Edited 4/27/2007 11:00 pm by SamT

3. 
   Danno | Apr 27, 2007 06:06pm | #6

   No one else addressed this, but I would think that a vapor barrier (polyethylene film sheeting) would be a good thing right under the slab--prevent water vapor from getting the slab wet. Concrete is hydroscopic, so I would think your slab would always be damp if you didn't use a VB under it. But, I am not a concrete finisher.

1. 
   bulwinkle | Apr 27, 2007 06:13pm | #8

   Over the Foam or under? I was planning gravel,plastic.foil foam barrier,then concrete.

   The plastic will eithier be glued or taped to the wall about 4" up the wall.

1. 
   Danno | Apr 27, 2007 06:22pm | #9

   I think what you propose would be fine--and less likely to put holes in the vapor barrier that way. Mainly want the VB somewhere between the wet ground or gravel and the slab.