Does there need to be a large temp difference to see if walls have insulation

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Permalink Reply by dale garren on December 12, 2010 at 6:24pm

Thanks John, i appreciate you taking the time to answer my quirey. do you know what the indoor ambient temperature was at the time of the photo? thanks again for helping me understand.

Permalink Reply by John Nicholas on December 12, 2010 at 7:37pm

Dale,

I looked up the BD test.  At the start of the Blower Door the inside was 70 and the outside was 43.  From what I remember, the outside didn't change much all day.

Permalink Reply by Rod Hoff on December 14, 2010 at 2:10pm

Judy

An important thing to remember is that the delta T (temperature difference) that's needed refers to "surface" to "surface" differences when investigation insulation issues.  Ambient temperatures can be a little misleading sometimes when we are investigating energy transmission issues.  For example, If the interior has a surface temperature of 70F and the exterior ambient is 30F we would think that the heat would move from inside to outside (2nd law of thermodynamics - hot to cold).  But what if you are looking (from the inside) at a south wall that has been effected by the sun for a few hours?  That wall might be 120F.  Now the heat movement is from outside to inside.  Missing insulation would look warm from the inside.  And if you go over and look at a north wall, which is not effected by the sun, missing insulation would look cool.  So, I always ask myself: What's the direction of the heat movement surface to surface, inside to outside or outside to inside?  And then I identify the color of the path of least resistance.  The framing members should be the path of least resistance in a fully insulated wall.  If insulation is compromised or missing then it will show as the path of least resistance.   That being said, air leaks usually require much less of a temperature differential, maybe only 3 degrees F and that is ambient to ambient, not surface to surface.  The sensitivity of the camera detector system can certainly have a positive or negative effect on the delta T needed in both scenarios.

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