Good afternoon

I have a question,
approximately by how much U-values is decreasing when the seals on the double pane windows damage.


Is it a double pane or triple pane window? Depends on if there was dead air or a specialized gas (usually Argon, possibly but less likely Krypton) between the panes. Those have different values. If gas leaked out, you will have a greater energy loss than if it was just air loss. That being said, while the window is not “performing as designed”, a blown seal on a double pane window is minimal when compared to the cost of a full window replacement. Pennies per month compared to hundreds of dollars depending on the size of the window. It takes a lot of “pennies per month” to add up to $250 or $300 or more.

This is normally covered under window warranties but those have changed drastically over the years. Some were lifetime. Some were for original owner only. They all differ.

it is a double pane, Aluminum, fixed, (1/4"x1/2"x1/4" )with air space, not gas
the regular U-value (when the window had original seals) 0.56
so by how much U - values is redused if the seals failed (damaged)

it is a double pane, Aluminum, fixed, (1/4"x1/2"x1/4" )with air space, not gas
the regular U-value (when the window had original seals) 0.56
so by how much U - values is redused if the seals failed (damaged)

The U-value of .56 would actually go up to a number value higher than .56 (likely). How much of change would also likely require scientific testing using sophisticated measuring devices or equipment. The lower the U Value number means a lower rate of heat transference. The lower the U Value the better the insulation of the window. Seal failure for a double pane insulated glazing unit would likely increase heat transfer and therefore increase the U-value number. Again, to know how much would require testing of the failed unit.

What you need this information for?

I can figure it out based upon a random sample of known failed windows but I’m not going to waste my time without sufficient reason.

The rate of increase would not be linear across the surface of fenestration. Do you want it averaged or a range?

Man you are grumpy David…
Hey Brother How you doing?

I’m doing some calculation for window losses, but if it a length processors to obtain it don’t do it, approximately is what percentage increase, i do not need exact.

The reason you are not getting a clear answer is because it is impossible to figure out.
Is there a total seal loss or a partial?
Is the window in a warm climate or cold climate?
Is the window decompressed or is it stable?

To many variables to answer it clearly.

My best WAG:
A single pane window has a U-Value of 1.22.
A double pane window has a U-Value of 0.70.
U-value loss would be somewhere in between that.
If half of the value is lost then the total U-value of a lost seal in this case would be 0.26

That is the best answer you will get likely.

At an inspection last week (9 degrees outside) the stationary side of the patio sliding door had lost its seal and was fairly cloudy inside. I took the opportunity to measure the inside temperature of the good side and bad side with my IR Thermometer. The difference was 2 degrees measured on the inside of the glass. Not a huge difference.

What did you set emissivity at? And what process did you use to come up with that reading?

How did you correct for temperature reflect?

And what was your transmissive value?

(Oh yea, you can’t do that with an IR thermometer can you?)

“Not a huge difference.”

There is a huge difference if you don’t do it right.