If there is that much condensation to block your view all morning and all evening, there is something else going on than just the addition of LowE coating.

As an example, I replaced my old Pella windows with new Marvins. I live in a more extreme climate than you, and the Pellas were not only covered in condensation, but in the winter I would get actual lines of ice on the inside of the windows - i.e. condensation that would freeze. I replaced with Marvin windows with LowE coating just before last winter's "polar vortex". For weeks the outside temperature was single-digits, while the inside temperature was 70 and I had a humidifier working - talk about your recipe for condensation! Yet all I would get on my new windows under those extreme conditions was a barely discernible line of minuscule water drops along the bottom edge, and that only rarely. So, your issue is something else than just LowE coating. I'll let the experts advise, but I wanted to give you my experience.

You're results would have been worse with clear glass. The new windows probably made the house a tighter not allowing the air to circulate thus trapping in warm moist air that is condensing on the cooler glass. You need to lower humidity levels, cracking the windows open would help short term simulating a leaky window. Just Google window condensation and you'll find many answers and almost all will point to high humity levels and none to low-e coatings unless on surface 4 which I don't,t think you have.

I would agree that there is something else going on here. Do you know what type of low-e coating was used and its surface location? It is possible that you purchased a profile that is not ideal for your area. Low e is a fantastic option, and when used properly it is beneficial in nearly every circumstance... but again, it needs to be used in the proper application.

.. Another possibility is simply the weather conditions. The only thing that the window itself (and/or the low-e) will affect is the surface temperature of the glass. The temperature outside and inside your home, along with the relative humidity are major factors as well.

Thank you all very much for your replies. One thing I need to point out that is being overlooked is that the condensation is on the outside. Hence, it is not conditions inside the house. My research indicates that outside condensation is caused by low E glass. Also, there was no condensation with the old single pane windows.

Thank you.

1)I did not overlook the fact that the condensation is on the exterior.
2) if your research is simply lumping all low e coatings together and proposing that they cause condensation, it is incomplete or being misinterpreted. Low e reflects heat either to the exterior or interior, depending on which direction/surface it is facing.
Bottom line is if the exterior glass surface is below the dew point, you will get condensation.

This post was edited by HomeSealed on Fri, Dec 26, 14 at 18:13

I assumed inside as well. You're going to have to adjust the exterior humidity.

Milgard uses SolarBan 60 and Cardinal 366 glass in their windows -- two of the most common Low-E glass types in the world. Millions of people have put that exact same glass into their own houses without condensation problems.

Anyway, if the issue is so important to you, it should not be very difficult to simply replace the Low-E glass units with plain clear glass units.

It probably won't change the condensation issue, but at least you'll have peace of mind and bleached floors.

Nothing you can do about exterior humidity levels.

The Low-e is slowing the loss of heat to the exterior pane of glass and therefore keeping it colder. That colder piece of glass is more conducive to the formation of condensation (i.e. dew point) during the morning hours.

Make sure your blinds on those windows are open and if you want to, direct one of your HVAC vents at the window so that it will keep it a bit warmer and keep it from getting down near that dew point temp.

"My research indicates that outside condensation is caused by low E glass. Also, there was no condensation with the old single pane windows."

Good morning Lumine,

LowE does not "cause" exterior condensation. As HomeShield and WoW both noted LowE coatings block radiant heat transfer thru the glass resulting in lower exterior glass temperatures. This is what IG units with LowE coatings are supposed to do.

As they also mentioned, condensation occurs on any surface when the temperature of that surface is below the dew point.

Moisture forming on the exterior of your windows is absolutely normal in the right conditions, and it's an indication that the windows are performing as designed, but it is also understandably frustrating for you because your view is being affected.

Basically, exterior window condensation is dew. It's no different than the moisture (dew) that you might see on your car windows or on your lawn. Same mechanism at work.

Exterior condensation formation on window glass is dependent on a number of different environmental factors such as exterior temperature, overhangs, prevailing winds, plantings, even cloud cover (or lack of), so that it is entirely possible that some of the windows in a home can have condensation and others nothing. In fact it is entirely possible that one window in a mulled set can have exterior condensation while the adjacent window has none.

Your old single pane windows didn't have exterior condensation simply because you were heating the glass enough to keep the surface temperature above the dew point, whereas now the combination of dual pane and LowE coating on your new windows is preventing the warmth inside your home from warming the outer glass which results in cooler exterior surface temperatures and condensation when the conditions are right.

Since this is a major concern for you, you may be able to eliminate or at least minimize the exterior condensation by heating the windows directly with a space heater. This kind of defeats the purpose of installing more efficient windows, but if you can warm up the interior glass enough then some of that heat will transfer to the outer glass and will hopefully raise the temperature above the dew point eliminating the condensation.

Adding ducts below the window probably will have no effect on the exterior condensation because the IG unit will likely be able to block that additional (indirect) heat from passing thru to the outer lite.

You might also try cleaning your exterior glass with something like RainX. I don't know if that works or not, but some people have claimed that it helps.

This post was edited by oberon on Sat, Dec 27, 14 at 9:34

I used to be a practicing thermodynamics engineer. I have not done a specific analysis butâ¦â¦

Unless there is fog outside (where the air temp has dropped below the dew point temperature), the glass temperature must be colder than the outside air temperature for condensation to form on the surface. (like in the summer on the side of cold beer).

The glass can only be as cold as it's lowest temperature heat sink/source. What this means is, if you neglect radiation, it is impossible for the glass to get cold enough to form condensation. When you take radiation into account, it is highly dependent on the surface properties of the glass and it's sink temperature. The sink temp for a clear sky is -460 F because you radiant to deep space. This will be the case even in direct sunlight (even though solar radiation is falling on the glass, it is still reradiating to space (-460F).

Low-e glass claims very low emissivity. Radiant Heat loss is proportional to emissivity for a given temperature difference (radiant heat loss is proportional to temperature difference to the 4th power (not very common in nature). Since the glass is warmed by interior heat, the addition of multiple panes of glass will greatly affect the glass surface temperature. IE - double pane glass will have a much lower surface temperature than single pane for a given radiant condition.

If you've made it this far, did you also go from single to double pane windows? This will have a much bigger affect than low-e glass. Is condensation only forming on windows with a view of the night sky (omnidirectional). If so an overhang that does not obstruct the view might solve your problem.

Aramaram - i know this is an old thread, but did you ever figure out a solution, I have the same issue.

Seeing as Mother Nature is driving the conditions that lead to exterior condensation, there isn't a whole lot you will do to impact that. On the one level, the same thing needs to happen to the window when you have interior condensation....in that...you need to get more heat/energy to the window. If you have any blinds or drapes, open them. Get more air circulation to the window and attempt to get it warmer.

San Fran is notorious for fog and condensation issues. You happen to live in a climate that is very conducive to condensation.