Condensation isn't necessarily due to the age of the windows or to the fact they aren't sealed properly. My guess is it's b/c it is either colder inside than it is outside and the temperature difference is the cause. Relacing the windows would be an obvious solution but in the meantime I would make sure there is unrestricted airflow around the windows.

If you have a forced air cooling system, I would set the thermostat to the run position for the fan as opposed to the auto setting. The main thing you want to accomplish is to reduce the amount of moisture in the house. When cooking, always run the exhaust fan and when showering, do the same and allow them to run for 20 minutes or so after you finish.

The house is under construction. No one lives in it. The new windows do not have condensation on them, only the old windows. There is no unrestricted air flow around these windows. There is no water service in the house.

Is the condensation on the inside or the outside surface of the windows?

On the inside.

Physically, your condensation problem is a puzzle.

Condensation forms on a window when the surface temperature of the glass goes below the dew point temperature of the air. The higher the concentration of moisture in te air, the higher the dew point temperature.

I am guessing from your home page that you building/remodelling in Louisiana? If so, I am assuming that in the middle of July the outdoors are both very hot and very humid.

In this situation, having exterior window condensation on the single pane windows, but not on the newer LowE dual pane windows makes sense - assuming that you were keeping the interior very cool. Interior window condensation in this situation is very odd.

If you have an exceptional amount of moisture inside your home:

1) exceeding the level of moisture outside,
2) thus raising the dew point temperature,
3) and if you cool your home so that the window temps go below the dew point temperature,
4) then it is possible that you could get interior window condensation under these conditions.

However, even given the above conditions, it would be much more likely that you would see this condensation on the newer dual pane windows rather than the older singles simply because the dual pane with LowE would be blocking the exterior heat from the interior glass - thus keeping the indoor lite cooler and more likely to be below the dew point.

The single pane windows, on the other hand, would be warmer and would be less likely to be below the dew point.

There has to be something very specific affecting your home and windows that is causing your interior condensation, but nothing (simple) comes to mind. As I said earlier, this is a puzzler.

So far as sealing your windows, I am not sure what you are asking. Are you planning to build your own "dual pane", or are you planning to mount one window over the other?

Thanks for the detailed response.

Yes, I live in southern Louisiana. The outside temps have been in the high 90Âs with 80%+ humidity. IÂm not sure of the inside temp because the house is under construction, 1897 square feet with very 2 small window units running but it is cool inside.

We're renovating/adding on to a 106+ year old house.

IÂm planning on taking the exact same windows that are across the front of the house and "doubling" them up, in effect creating a double paned window. There will be a least 2" of space between the windows due to the frames. I donÂt know if just caulking around the windows would be enough or do I need to take these out and put weather stripping around all of them, then caulk. Right now, there is air infiltration around the old windows. I have to sand and paint them before sealing around the individual panes.

The new Low E windows have no condensation at all.

You might be better off not sealing the windows tightly.

You will not be able to stop moisture from getting between the two windows, so you will need a way to exhaust that moisture. Sealing the windows tight could result in trapping moisture between the frames and could result in problems down the road.

Are you planning to double the windows srictly for energy performance?

I looked closely at the windows this morning and the condensation is on the outside. I'm sorry.

Yes, I was only doubling them for energy efficiency.

Okay, that makes much more sense. Condensation on the exterior is a normal occurrence as you described it.

In your environment, the primary source of heat gain in your home is from the sun (go figure). Doubling your windows really isn't going to help you a lot in that area. It will help with keeping ambient heat out - but the heavy duty solar gain is going to pass thru the doubled windows just about as easily as it passes thru the single window.

A low solar gain LowE coating is what blocks that solar heat - as well as a good bit of the radiated ambient as well.

Just a suggestion, but you might want to consider a solar control window film or exterior solar shade for blocking that heat and keeping it outside.

Either of those options should provide better overall thermal performance in your environment than doubling up the windows will, and should be considerably easier in time and trouble.

Just food for thought.

Thank you.

Film would definitely be easier. LOL