For those type of thermometers to be accurate on a
reflective surface, such as glass, you have to lower
the emissivity of the glass. You can do it by putting
a piece of flat black tape on the glass first, and then
let the tape aclimate to the glass temp. before using
the thermometer on the tape. Let us know what you find.

To keep the post short, I left that off but, yes, I put on a piece of black electrical tape beforehand and then shot the laser onto the tape, being careful not to measure if the window was in sunlight and warming the tape by light. So, are my windows too cold or is this just what windows typically do? I thought I would ask the tech help at Andersen also since I assume they have specs for their windows.

window values are U-factors & solar heat gain coefficients.
the lower these numbers, the better the preformance of
the window.
visit www.nfrc.org for unbiased, info on windows for your
climate

check the posting out I found on the window forum

Here is a link that might be useful: crash course in NFRC ratings

U value is basically 1/R.

The use of U values is to try and 'hide' how poor even the best windows are at slowing the movement of heat.

Pella has windows from U = 0.23 to 0.82 in a high end line.

That is about R 4 to R 1.2

OUCH!

There is just no good way to really increase the R value of glass.

My guess is that is as good as your windows will do.
If you have any single pane glass in your home, measure
that, for a comparison. I have had thermo pane windows
develop leaks in my home and it shows up as mildew
between the panes, so if your windows are clear, then
I would not suspect a leak.

Any glass window, including thermopane is a good conductor of heat compared to, say, an insulated wall. If you had single pane, the windows would be even closer to the outside temp. I agree that the windows are probably fine and that this is not an indication of window failure unless you see visible condensation.

Glad to see that Oberon's advice is still being kept around.
Great info, well explained.

Hi ERLA - ltns!

jaansu,

I am guessing that you have clear glass over clear glass IGU in your windows. The temperature measurements that you gave are not unreasonable for that configuration.

As a general guideline, dual pane clear glass windows will have a center-of-glass temperature of around 43 when the outside temperature is 0° with no wind or solar interference. Adding LowE coating and argon fill will increase that temp up to about 57° (when zero outside). These are center-of-glass measurements, and can vary when measuring the glass outside of the center or when measuring various compnents of the window sash / frame.

Your windows are 17 years old. I would guess that they don't have a LowE coating or argon fill. Even today, only about half of windows being produced have a LowE coating - which surprises many people who assume that the coating and gas infill are "standard" features in all windows.

There isn't much that you can do about raising the indoor temperature of your windows. I would recommend that you ensure that the windows are tightly sealed and that the weather-stripping is in good repair.

You can also add the interior shrink-film plastic which will help limit both air infiltration and will add an insulating airspace between the glass and the plastic which may help the temp climb a little....or some folks cover their windows with exterior plastic during the winter for the same reasons. Hopefully, doing a few little things can help.

I am not a big fan of either insulating curtains or shades since they tend to block interior heat from the windows which can lead to excessive condensation and potential moisture-related problems particularly in a cold environment.

And a bit off topic, but since it showed up on the thread...

U-value does equal 1/R and by strange coincidence R-value does indeed equal 1/U  but there is no vast conspiracy of window companies (and NFRC by extension) deciding to list U-value rather than R-value in order to "hide" poor energy performance  actually there are very sound reasons for using U versus R when dealing with windows. And, as a matter of fact, R-value can be (and sometimes is) used by window sales folks to "hide" the true performance of a window.

Windows performance is presented in U-factor simply because it is a more accurate way of describing window performance. While U-factor can be converted to R-value because it is a more intuitive number and it is easier for many people to "see" the overall performance, if an energy rater (for example) wants to determine the overall performance of the window and wall system the energy rater must convert back into U-value for the calculations.

R-value is a measure of resistance to conductive heat loss "thru" a material or group of materials. U-value is a measure of heat transfer "across" a group of materials.
Windows are an "across" product.

The primary disadvantage of using R-value for a window is that what is often given is the center-of-glass reading, which while technically correct, can be misleading when dealing with the overall energy performance of the unit (which I alluded to earlier in this post).

U-factor, as listed in the NFRC directory and on the window label of units certified thru the NFRC, is the actual overall energy performance of the window system and not a number related to the best-performing portion of the unit.

No one is hiding anything - it is simply a more accurate number.

Thanks Oberon, a well written and informative reply. Measureing the center of window temp a couple of times at night while outside temp was 25 F indicated all windows were at 40-46 F, except for a few outliers in the 30s. Since your statistics took into account an outside temp of 0 F for a similar internal window surface reading, it seems my windows are less efficient. There is also the case of the few windows that are distinctly colder and I can see a faint outline of an oval on two windows, which I have been told may be due to collapse of the two panes to touch each other.

Perhaps I should still call in Andersen? They seem very willing to examine my windows but I would like to have an idea beforehand if I should push for replacement or if this is acceptable. Manufacturers do occasionally put out inferior lots and it could be that my house didn't get the standard. What do you think?

jaansu,

You are quite welcome.

After reading your last post I do have to make a correction from my previous post...I simply missed the "Andersen" part of your original post.

Andersen was filling their IG's with argon 17 years ago, but unfortunately the seal system in use at the time was not argon impermeable. Argon tended to leach out of the IG thru the materials that made up the IG seal system.

This was not a seal failure in the sense of the IG filling with moisture-air and becoming cloudy, rather in this case the seal held, but it could not contain the argon.

The second problem was that while argon leached out, the seal did keep air from penetrating and replacing the argon. Nitrogen will penetrate that seal system, but at a rate about 3 times slower than the argon heading in the other direction which resulted in IG units with "collapsed" glass - exactly as you describe.

Basically, there is a partial vacuum between the lites and the glass simply isn't stiff enough to avoid collapsing inward in the presence of the vacuum. As the airspace narrows between the two lites, energy performance goes down. When the glass actually touches (the oval) then energy performance is the same as having a single lite rather than an IG with two lites.

The solution is to call Andersen and tell them that you have collapsed glass - they will fix it and you will have better performing windows again.

There are three "fixes" for collapsed glass.

First option, a technician will drill a small hole in the frame of the IG allowing air into the unit until it has reached the same pressure inside the space as outside. He or she will then fill the hole and the window will perform as designed - minus the original argon which is long gone.

Second option, AW will replace the IG (glass portion) of the window (not sure how often they are doing this one).

Third option, AW will replace the entire sash - which is a pretty common fix.

Drilling the hole and re-expanding the window will cost you nothing. Glass and sash replacement will cost you nothing for the new materials, but labor to install the new parts is not covered by warranty. Sash replacement is a fairly straightforward DIY project if you are so inclinded and want to avoid any labor charges.

Call Andersen's service line and tell them that you have collapsed glass - and while I don't compare or generally comment on specific window companies - I will say that no one in the industry has better customer service than Andersen. They will help you out.

Jaansu, try taking the temperature of the glass from the
outside and compare it to the outside air temperature. I think this could be more accurately done at night, so the
sun's radiation doesn't effect your readings. This seems
to me, to be a more accurate way of finding how much
heat is escaping through the glass. The inside surface of your window is heated by your house heat, which I would think would skew the results.

U-values are used in the calc of heat loss. Take temperature difference in F (inside temp minus outside temp), multiply by Area of glass (square-ft) and then multiply by the U-value (Make sure units of u are: BTU/Sq-ft/deg F) This give BTU/hr lost. (your boiler is rated in BTU/HR.) R values are used because they can be added for a particular assembly: Rwindow + Rair-space + Rdrapes, etc. When they are all added up, you then take the inverse to get the u-value of the enire assembly. (Utotal=1/Rtotal) Use this u-value to determine the heat loss through the layers. U-values can not be added up directly, but R can. R is very good for adding the differenct values for a wall assembly (Rsiding + Rplywood + Rinsulation + Rdrywall, etc). Use 1 divided by the total R to get U of the wall. Mutliply this U by the temp difference and area to get the conduction heat loss. There are other heat losses as well but that's another discussion (and a boring part of my job)

jaansu,

I was curious if you called Andersen about the collapsed glass issue - and if so what is your status with the windows?

oberon

I haven't called them recently. When I spoke to a rep before I started this thread, it seemed they were very willing to replace defective windows but wanted to send someone to check out the windows if I had multiple failures. Since the warrenty runs another couple of years,and I don't expect to do any replacing while it is freezing outside, I'm taking my time and want to carefully examine all the windows so I can point out what windows need to go. The rep had said if I place a finger on each side of the pane, that I should be able to determine which windows have collapsed. I want to try this on all the windows.

So far, all I know for sure is that two front windows show a faint oval, which seems to be the touching panes. These spots are particularly cold as well. Curious it should be both adjoining windows and both the top sash?

You do realize this is a 10 year old post?

Yes, and you saw it. What do you think?

Think somone must have reported it as spam because it is gone.......................