Single pane Temp VS dual pane

**Scuba_Dave** · 01-21-2009, 06:08 PM

I thought this was interesting from a Green site I visit:

I was playing around with my new IR Thermometer this morning. It was 70 degrees in the house, 39 degrees outside. According to my IR Therm - the dual pane windows were at 67.8 degrees; the single pane windows were at 63.1. Just now I thought maybe I should have measured the frames... since the old frames are aluminum - new ones are vinyl... Ah, either way, you get the point. Even the glass temps are very different.

**alternety** · 01-22-2009, 01:57 PM

Actually somewhat scary. If they do not understand that this is HOW IT WORKS and the measurements are a revelation, they need more training.

**Scuba_Dave** · 01-22-2009, 02:41 PM

Originally Posted by alternety

Actually somewhat scary. If they do not understand that this is HOW IT WORKS and the measurements are a revelation, they need more training.

Who is "they"
Why would a homeowner who just bought this device need more training? And in what? The whole purpose of buying the device was to track down heat/cold leaks that can't be seen

The point was the Temp difference & how much
Frankly I'm surprised there wasn't more of a difference between the two

**CarlH** · 01-22-2009, 03:05 PM

Originally Posted by Scuba_Dave

Frankly I'm surprised there wasn't more of a difference between the two

Tell whoever did this to repeat the test when it is 20F outside or colder. I don't know if that would give a wider spread in the measurements or not. Also, repeat the test from the outside.

The next test would be to throw a low-e window into the mix.

**alternety** · 01-22-2009, 04:31 PM

Dave; the point was that anyone buying windows (a probably unobtainable goal) would understand that the better the window, the higher the internal pane temperature (i.e., least heat loss differential temperature).

**Scuba_Dave** · 01-22-2009, 04:56 PM

hmmmmm

I was going to ask him if it was LowE
Now I can't find his post

**Nate R** · 01-22-2009, 05:02 PM

The bigger issue is the measurement method. Those things SUCK for accuracy. How big a spot was he measuring? (Depends on beam width) From what distance? What's the Emissivity of the glass? This setting is CRITICAL for the infared thermometers.

**Scuba_Dave** · 01-22-2009, 05:11 PM

Originally Posted by alternety

Dave; the point was that anyone buying windows (a probably unobtainable goal) would understand that the better the window, the higher the internal pane temperature (i.e., least heat loss differential temperature).

Ya think?

**alternety** · 01-22-2009, 05:16 PM

The only way to correctly evaluate a window is to use a combined loss value that includes losses at center of pane and peripheral losses (frame, separators, etc.). This is actually a differential equation where losses vary based on the glass performance (essentially in free space), proximity to the edge of the window (and the conductance of the edge), as well as losses due to air leakage, convection and radiation.

Using a spot IR meter does not provide useful quantitative loss information on whole window loss. It will give you a general ratio of the loss contribution of the glass itself. If glass A has an R value of 2 and B has an R value of 6, useful information can be derived. But if A has an aluminum frame and B has a significantly better insulating frame material ,and A has big air gaps (e.g. rotten air seals) that loose hot air but B has tight seals, and A has no radiation frequency selective layers and B does, the whole equation changes.

Whole window numbers for the installed environment are the only truly useful comparisons.

hj · 01-22-2009, 05:35 PM

Dual panes are better than single panes, and triple panes are even better. I guess the question is why the person was surprised by his readings. That is the way they are supposed to be.